Aspects of Geology in Planning F. G. Bell, J. C. Cripps, M. G. Culshaw & M. O'hara Introduction

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Aspects of geology in planning

F. G. Bell, J. C. Cripps, M. G. Culshaw & M. O'Hara

ABSTRACT: The planning of man's environment is a complex operation which requires the interaction of many disciplines. Generally speaking, the physical development of society occurs by the implementation of a series of separate, but converging, aims which may be expressed in terms of, for instance, improvements to living conditions, public health or mobility. A development plan usually attempts to achieve these aims at minimum financial cost while reconciling many conflicting influences. So far as the use of land is concerned, since some land is inherently more suitable for some purposes than for others, there are clear cost implications in implementing a particular development plan and savings may be possible if the ground conditions are considered at an early stage. However, problems often arise with quantifying this cost due to a lack of appreciation of all the effects of a plan, including unexpected and undesirable ones. Since many natural systems pose threats to society, they should be taken into account during planning. The monetary costs may be less tangible, but security of life, disruption to production and destruction of property all reduce the well-being of society. Whether the causative hazards are the result of either planned or unplanned changes to the environment, or due to naturalprocesses, they can only be successfully predicted or avoided if their mode of interaction with human activities is understood. In this paper the opportunity is taken to explore some of themore important geological factors which may significantly influence the planned use of land. Both natural and man-made geological hazards are considered. In addition, attention is given to the sources and interpretation of geological information in the context of planning.

Introduction Over recent years public concern regarding the alteration and degradation of the environment has caused The ultimate objective of planning is to determine a governmental and planning authorities to become more particular course of action and so involves attempting to aware of the adverse effects of indiscriminate develop- resolve perceived problems. Although the policy which ment. As a result laws have been passed to help protect the develops from planning embodies a particular course of environment from spoilation. Most policies which deal action, planning proposals are often controversial in that with land-use are concerned with either those processes they may offend one or more sections of the community. which represent threats to life, health or property includ- Hence, in the last analysis, planning policies are the ing, for instance, hazardous events, pollution of air or prerogatives of government since legislation is necessary water; or the exploitation, protection or conservation of to put them into effect. natural resources or the restoration of despoiled areas. Land-use planning represents an attempt to reduce the Since land-use inevitably involves the different de- number of conflicts and adverse environmental impacts velopment of particular areas, some type of land classifi- both in relation to society and nature. In the first instance, cation(s) constitute the basis on which land-use planning land-use planning involves the collection and evaluation is carried out. However, land should also be graded of relevant data from which plans can be formulated (Fig. according to its potential uses and capabilities. In other 1). The policies which result depend on the economic, words, indices are required to assess the environmental sociological and political influences in addition to the status of natural resources and their potential. Such perception of the problem. In this context, the primary indices should establish limits, trends and thresholds, as role of engineering geologists should be to provide well as providing insight that offers some measure of planners and engineers with sufficient information so success of national and municipal programmes dealing that, ideally, they can develop the environment in har- with environmental problems. For example, in 1976 the mony with nature. Indeed, as indicated in Fig. 2, the US Geological Survey adopted a land-use and land cover geologist can offer much useful information at all levels of classification system which has been used to compile planning and development from the initial identification maps and thereby to provide a land-use inventory of the of a social need to the construction of a dam, road, airport whole country by 1985. or town that is required to satisfy that need. Even after Obviously one of the aspects of planning which construction, further involvementmay be necessary in the intimately involves geology is the control or prevention of form of advice on hazard monitoring, maintenance, or geological processes or hazards which mitigate against remedial works. The most convenient method of provid- the interests of man. The development of planning ing the necessary geological information is usually, at policies for dealing with hazards in particular, requires an least partially, in the form of a map. assessment of the severity, extent and frequency of the

From CULSHAW, M. G., BELL, F. G., CRIPPS, J. C. & O'HARA, M. (eds) 1987. Planning and Engineering Geology, Geological Society Engineering Geology Special Publication No. 4, pp. 1-38. Downloaded from http://egsp.lyellcollection.org/ by guest on September 27, 2021

2 F.G. BELL, J. C. CRIPPS, M. G. CULSHAW ~ M. O'HARA

the ground conditions can affect both the viability and implementation of planning proposals. The incorpora- [ SOCIAL NEED] tion of geological information into planning processes should mean that proposals can be formulated which do IENGINEERING not conflict with the ground conditions present. GEOLOGY IPaNNE"sl IMAPSt 1 Conservation, restoration and reclamation I of land Hazards1 - 1:5o.ooo ,{NATIONAL I Land is one of the most important of human assets and since there is insufficient to satisfy the demands placed I upon it, this resource should not be wasted. What is more, + Foundation 1:5.000 '~ DISTRICT] derelict land has a blighting effect on the surrounding area Conditions , which makes its restoration highly desirable. Conservation is concerned with safeguarding natural phenomena and the preservation and improvement of the -!- geotechnical 1:500 quality of the environment. As such it is closely associated values with the geology as geology and environment are intimately interrelated. However, in the case of the mineral extraction industry, the geologist may find himself in conflict with the conservationist. On the other hand ~REMEDIAL l geological knowledge should be made use of in conservation programmes since these should seek to make the wisest use of natural resources and in this concept there is no conflict with the geologist. I NEED FULFILLEDI Conservation is not simply preservation, it seeks to improve existing conditions rather than simply maintaining the status quo. Hence conservation does involve the reconciliation of differing views so that the best com- FIG. 1. The relevance of engineering geology to different stages of promise can be reached. Obviously in this context land- planning and development. (After Forster & Culshaw 1987). use is important. In some instances the same land can be used simultaneously to cater for several needs, whilst in hazard in order to evaluate the degree of risk. Once this others the uses to which it can be put are consecutive has been accomplished methods whereby the risk can be rather than concurrent and the final effect can be either to reduced have to be investigated and evaluated in terms of restore the land to its original use or to a new use which public costs and benefits. The risks associated with forms an acceptable part of the landscape. Thus a geological hazards may be reduced, for instance, by sequence of events must be planned to ensure the greatest control measures carried out against the hazard produc- efficiency in the use of resources and that the most ing agent; monitoring and warning systems which allow acceptable final state is achieved. Hence in such situa- evacuation; restrictions on development of land; and the tions, the geologist must be involved with planning from use of appropriate building codes together with structural the onset. If this is not done, then natural resources may reinforcement of property. In addition, the character of be sterilized as a consequence of premature alternative

Public initiative and response l 1 t ' 1 PROBLEMS COLLECT REVIEW AND AND FORMULATE AND IMPLEMENT DEFINE GOALS INTERPRET PLANS ADOPT PLANS AND DATA PLANS OBJECTIVES

Evaluate impacts-environmental, social, economic, fiscal /

COLLECT DATA FORMULATE PLANS IMPLEMENT PLANS Earth Science and other Land use Zoning and subdivision regulations information Watershed Erosion and r,edimentation control Background studies Natural resources ordinences Existing land use Hazard mitigation Building end housing code= FIG. 2. Diagram showing the land- Transportation Open space Environmental impact statements Economic Waste management Capital improvement programs use planning process. (After Wil- Political Public facilities Health and sanitation codes liam Spangle and Associates et al. Social Land capability studies 1976). Downloaded from http://egsp.lyellcollection.org/ by guest on September 27, 2021

ASPECTS OF GEOLOGY IN PLANNING 3 development. The classic examples are the developments survey and investigation. The exact boundaries of the site of urban areas over valuable surface mineral deposits, and the various physical features it contains are recorded which could have been extracted and the areas then during the survey and boreholes may be sunk to assess its developed. geological character. These data allow plans to be drawn Obviously developed and developing societies make and the restoration project to be designed. essential demands upon land which frequently mean that The reclamation of land involves its upgrading to a use it is degraded. An appreciable contribution to the general which is considered more beneficial to the community. economy can be made by bringing this derelict land back The reclamation of swamplands and marshlands by into worthwhile use. Eventually such land must be drainage so that they can be used for agricultural or other restored. Whatever the ultimate use to which the land is purposes illustrate this. Some impressive examples of put after restoration, it is imperative that it should fit the reclamation are provided by the various schemes under- needs of the surrounding area and be compatible with taken in the Netherlands by which land has been other forms of land-use that occur in the neighbourhood. reclaimed from the sea, the Zuider Zee scheme and the Accordingly the planning of the eventual land-use must Delta scheme offering noteworthy examples of man's take account of overall plans for the area and must ingenuity. endeavour to include the ecological integration of the restored area into the surrounding landscape. Restoring a site which represents an intrusion in the landscape to a condition which is well integrated into its surroundings in fact upgrades the character of the environment far Engineering behaviour in relation to ground beyond the confines of the site. conditions Two of the major causes of the dereliction of land are the extraction of minerals (Fig. 3) and the disposal of The engineering design of structures is based on detailed waste products from mineral workings in the form of measurement and interpretation of the behaviour of the spoil heaps and tailings lagoons. Mineral extraction may soils and rocks liable to be affected by construction work. also cause water pollution. In practice, the restoration In this context probably the most significant features of and conservation of derelict sites involves the use of soils and rocks are their capacity for bearing loads planning controls. Hence conditions are attached to without excessive settlement, their volume change charac- ~ planning permissions granting mineral developments and teristics, their excavatability and their intrinsic and en these apply not only to the form of development permit- masse stability (Bell 1983). The engineering behaviour of ted but also to the ultimate state of the land after soils and rocks is a product of their composition, extraction ceases. For example, the after-use of some sites microfabric and mass structure. In turn these features are where minerals have been worked has caused problems, functions of their mode of formation and subsequent notably when pollution has resulted from their use for the history. It is important to appreciate that due to geologi- disposal of toxic wastes. On the other hand, the use of cal proceses, especially weathering, the engineering pro- such sites as recreational areas has provided additional perties of soils and rocks change with time. The nature, amenities for the communities they serve. Again this extent and rate of occurrence of these changes are emphasizes the need for thorough planning. influenced by the character of the geological material A preliminary reconnaissance of a derelict site is concerned and the environmental conditions. desirable to determine the sequence of work for the site Great care must be taken when making generalizations about the engineering behaviour of geological materials. Not only may their properties be significantlymodified by the presence of minor constituents but due to the effects of sample disturbance, stress relief and the absence of large scale discontinuities, data derived by performing tests on relatively small specimens may differ significantly from the in situ behaviour. Another important feature of many soils and rocks is the anisotropy which many display. Whether this is due to mineralogical alignment, systematic variations in composition or the preferred orientation of discontinuities within the material, it results in significant changes in the properties with direction. It is convenient to deal with the engineering behaviour of geological materials in terms of unconsolidated deposits, sedimentary rocks and crystalline (that is, igneous and metamorphic) rocks. The opportunity is taken to elucidate the engineering behaviour with respect to bearing capacity, foundation settlement, excavatability FIG. 3. An example of china-clay workings in Cornwall. These and other properties in terms of geological features. The produce major scars on the landscape, as do the associated spoil causes of variation in the geotechnical parameters also heaps. form part of this discussion. Downloaded from http://egsp.lyellcollection.org/ by guest on September 27, 2021

F. G. BELL, J. C. CRIPPS, M. G. CULSHAW t~ M. O'HARA Unconsolidated deposits Fine-grained, saturated, sandy and silty deposits can be caused to liquify by earthquakes and other shock loadings The superficial materials which mantle many of the solid (Seed et al. 1977). Hence a large reduction in bearing geological formations comprise gravels, sands, silts and capacity occurs and the material also may become clays, and mixtures of these which generally exist in a unstable in slopes. loose, disaggregated state or 'soil like' form. However, Clay soils are variable in bearing capacity and volume some may be denser or harder than others due to some change characteristics, their properties being dependent degree of consolidation or some amount of cementitious on a number of factors including water content, density material precipitated in their pore space. and composition. Generally speaking low density depo- The engineering properties of these materials depend sits are weak and provide inadequate foundations for primarily on the composition and particle size distribu- most structures. Clays which contain minerals such as tion of the constituents, and the fabric of the deposit. In montmorillonite, a common weathering product of vol- turn these features are controlled by many factors, canic rocks, are particularly weak and compressible. The including the type of parent rocks, the type of breakdown proportion of clay-sized material present in a deposit also processes, the prevailing climatic conditions, the condi- influences its properties. For instance, an increase in the tions both of transportation and of deposition of the clay size fraction causes a reduction in strength and debris and the post-depositional history. Nonetheless, increase in compressibility. although particular climatic regimes (notably glacial, Many clay deposits are subject to swelling and shrink- tropical and arid) give rise to specific suites of deposits, age in response to changes in water content. Grim (1962) since particle size distribution exerts a major influence on distinguished inter-particle from intra-particle swelling. the engineering performance of soils, and is therefore the The former refers to the uptake of moisture both onto the most significant factor in their engineering classification, external surfaces of clay particles and into the pore spaces it is sensible to consider soils in terms of granular and between them. Such swelling may occur in all materials cohesive varieties. An exception would be organic soils, but it is much more significant in clayey deposits. Intra- these constitute a separate category. particle swelling is a property of the smectite group of clay The engineering properties of granular soils are con- minerals, in particular montmorillonite, although vermi- trolled by physico-chemical interparticle forces. These, in culite and some varieties of chlorite also swell. Soils turn, depend on the type, shape and size of the grains. containing significant proportions of these minerals Although when a stress is applied to a soil some grains undergo large volume changes on wetting and drying. may break, unless the stress is high, the major effect is to Many soils in Britain, especially in south-east England, cause them to roll, slide or become translated into new possess a large potential for significant volume change positions within the soil mass. The opportunity for grain due to changes in water content. However, owing to the movement, and hence the deformability and strength of damp climate, in most years volume changes are res- the soil, is controlled by the packing of the grains or the tricted to the upper 1.0 to 1.5 m (Driscoll 1984). When density of the soil as well as the external stress conditions vegetation is cleared from a site in semi-arid regions, its and other factors which govern the interparticle frictional desiccating effect is also removed and the regain of forces. moisture by clay leads to swelling. This process has Most gravels, sandy gravels and sands, if in a medium proved a significant cause of foundation heave in parts of dense or denser state have relatively high bearing capacity South Africa (Williams & Pidgeon 1983) and the southern and undergo little compression when loaded. These USA (O'Neil & Poormoayed 1980). materials may be excavated with reasonable ease, Under semi-arid conditions clay soils may develop a although excavations often require support. Looser gra- desiccated crust. Evapotranspiration in temperate cli- nular soils and silts have less favourable properties, mates may also produce this effect, although to a lesser particularly if a proportion of clay is also present. These degree. Such a crust may provide an adequate foundation materials have lower bearing capacity and undergo for light structures, but care must be taken to ensure that greater compression when loaded. All granular soils have the underlying softer materials are not overloaded. high intrinsic permeability, in fact many of these deposits Furthermore the possible adverse consequences of serve as aquifers and excavations below the water table natural or induced water content changes must also be are liable to flood. Furthermore, seepage pressures, if considered. excessive, may cause the collapse of unsupported excava- In arid and semi-arid areas the precipitation of various tions below the water table. dissolved components of groundwater can give rise to Certain silty soils which form under semi-arid climatic surface hardening of silty clay soils by the development of conditions exist in a metastable condition such that they crusts or cretes. Beneath the crusts such soils are liable to are liable to undergo large reductions of strength and undergo marked volume changes if they are subjected to volume if wetted or if loaded beyond a particular value. wetting or drying and the possibility of overloading Unlike water lain silts, terrestrial silty clays and loess are underlying weaker horizons should also be borne in mind. particularly prone to this type of behaviour (Clevenger Laterite is a residual, generally ferruginous, clay-like 1958). They consist of loosely packed grains and the deposit which generally occurs below a hardened crust or porosity of the material may be further enhanced by the hardpan which can be up to 7 m thick. These materials presence of fossil root-holes lined with carbonate mater- typically form in tropical areas. Laterite, particularly if it ial. Inundation causes collapse of the soil structure; even is mature usually provides a good bearing stratum under self-load. Downloaded from http://egsp.lyellcollection.org/ by guest on September 27, 2021

ASPECTS OF GEOLOGY IN PLANNING 5 although the strength may decrease with depth and pressures are raised, the sheets are inappropriately loaded significant seasonal volume changes may occur. Due to or support is removed. the presence of swelling clay minerals, tropical black clays The low bearing capacity and highly compressible are also liable to swell and shrink in response to changes nature of peat and other organic soils make them in moisture content. troublesome from an engineering viewpoint. (If the Quick clays are deposits which have little or no shear organic content of a soil exceeds about 20%, then its strength once disturbed; in extreme cases they assume the consolidation behaviour becomes increasingly domi- properties of a viscous fluid. They have a restricted nated by this component). Peats are typified by high geographical distribution, occurring in certain parts of values of void ratio and extremely high water contents. In the northern hemisphere which were subjected to glacia- fact shrinkage in the range of 10% to 75% of the original tion during Pleistocene times. These materials, which volume is liable to accompany drainage. Such soils consist of a loose arrangement of equi-dimensional undergo large settlements when loaded and are prone to aggregations of clay particles and small quartz grains, are rotational failure but instability by spreading is also typified by the Leda Clay of Canada (Gillott 1979) but probable. certain clays in Alaska and Norway have similar properties. They all have low bearing capacity and undergo large Sedimentary rocks settlements when loaded. In addition, a loss of bearing capacity or slope failure can be precipitated by increases Denudation of the land surface leads to the breakdown of in water content, loading or increases in pore water the rocks and soils. The products of degradation may then pressure. be transported, deposited and subsequently lithified to Tills are formed from material that has been trans- form a variety of different rock types. The engineering por;~ed by an ice sheet and then either deposited on the properties of sedimentary rocks depend mainly on the ground beneath the ice (lodgement till) or left on the composition of the constituents and the mode ofintergra- ground following the melting of ice (ablation till). The nular attachment. In addition, the engineering properties composition of tills is very variable and material which of rock masses are also influenced by the presence of has been transported hundreds of kilometres may be joints, mineralogical alignment and other structural mixed with locally derived material. The variable nature features which, in the case of sedimentary rocks, include of these deposits gives rise to variable engineering bedding surfaces. performance; with differential settlement frequently caus- The lithification of a loose sand or mud into sandstone ing particular problems. The higher angles of shearing or mudstone respectively comes about by the consolida- resistance displayed by many of these deposits compared tion of the sediment due to the weight of overlying with clays with a similar grading is due to the fact that sediments. This causes re-arrangement of particles, pac- much of the fine fraction consists of rock flour and finely king them more densely together. At the same time water ground quartz rather than clay minerals. is squeezed out of the sediment and diagenetic processes Owing to its overconsolidated nature, caused by pre- bond the particles together by a combination of the loading by ice, dense lodgement till is relatively incom- precipitation of mineral cements in the pore space, the pressible. Its relatively high strength provides good formation of overgrowths around existing grains and the bearing capacity. If, however, the deposit is variable in intergrowth of grains due to pressure point solution. In character, then problems of differential settlement may the case of fine grained, muddy sediments Van der Waals arise. Indeed the compressibility increases, and strength forces, electrical charges and molecular bonding forces, decreases as the clay content increases. Ablation till tends also operate between the particles. to have a lower density, lower strength and higher Overconsolidated clays and mudrocks are formed by compressibility than lodgement till. Lodgement tills, the consolidation, in some cases accompanied by cemen- particularly clayey ones, contain fissures which according tation, of clay or mud deposits. Various types of rock are to McGown et al. (1974) may display a pronounced included in this category, for instance, claystone, mud- preferred orientation. These structures exert a strong stone and shale. A distinction is made between overcon- influence on the strength, deformability and other engi- solidated clays which have been loaded by overburden neering properties of the deposit. that has been subsequently totally or partially removed The deposits produced by glacial meltwaters include and normally consolidated clays in which the present varved clays which accumulate in proglacial lakes. Due to overburden is the maximum load imposed on the sedi- seasonal deposition, these clays are characterized by ment. Since overconsolidated clays retain features gained alternating laminae of finer (clay) and coarser (silt) sized during consolidation they have greater density, higher material. Since most varved clays are normally consoli- strength and lower compressibility than normally conso- dated or only lightly overconsolidated they have low lidated clays. strength and high compressibility. During consolidation, concomitant recrystallization Periglacial activity during Pleistocene times has dis- and the rearrangement of particles, particularly those of posed many slopes to mass instability and has also platy habit (for example, clay minerals and micas), more resulted in the brecciation of many geological formations. or less perpendicular to the overburden pressure gives rise Hillside solifluction sheets, in particular, are highly to the characteristic fissility exhibited by shales. The susceptible to translational failure as they rest on existing anisotropy which this imparts on the material and the shear surfaces. Movements are probable if pore water tendency to split into thin sheets may be enhanced by the Downloaded from http://egsp.lyellcollection.org/ by guest on September 27, 2021

6 F.G. BELL, J. C. CRIPPS, M. G. CULSHAW ~ M. O'HARA presence of sub-parallel bedding planes, Iithological dation, sometimes assisted by bacteria, contributes to the laminae or fissures. breakdown of the material. Furthermore, the combina- Mudrocks and overconsolidated clays vary widely in tion of sulphate ions (one of the breakdown products) their engineering behaviour, depending not only on with carbonate to form gypsum can exert pressures of composition, but also on their state of induration. crystallization sufficient to lift lightly loaded structures Accordingly, Mead (1936) divided shales into compac- (Nixon 1978). tion and cementation types. Compaction shales derive Slopes in overconsolidated clays and mudrocks are their competency solely from the density attained due to liable to fail if the slope becomes over-steepened by burial, whereas, induration by mineralogical bonding erosion or excavation. The design of slopes should not be renders cementation shales stronger, less compressible carried out on the basis of the peak shear strength and more durable. parameters since the effects of stress relief and weathering The mineral composition of these rock types is very degradation are liable to reduce the strength to its relevant to their engineering behaviour. For example, remoulded or softened value (Skempton 1970). For steep Burnett & Fookes (1974) found that an increase in the slopes the most common mode of mass instability is clay fraction correlates with increased plasticity (and rotational failure, but other styles including shallow non- hence compressibility) and reduced strength. As far as the circular rotational slips and translational slab slides occur Oxford Clay is concerned, Russell & Parker (1979) on slopes of lesser angle. Slopes as shallow as about 8 ~ indicated that a reduction in strength also occurs with have been found to be unstable in London Clay although increasing content of expandable clay (for example, only in the presence of adverse water conditions. In- montmorillonite) in the clay fraction. Furthermore, creases in the water content of landslip disturbed material enhanced strength correlated with the increasing presence frequently gives rise to associated mudflows. of mineral cements, in particular calcite and pyrite. The engineering behaviour of sandstone and siltstone is Cripps & Taylor (1981) noted that increased induration is a product of the composition and packing of the cons~it- related to increases in previous maximum overburden nuent grains, as well as the amount and type of cement pressure and geological age. holding the grains together. In addition, discontinuities In an unweathered condition most overconsolidated especially bedding planes and joints, exert a control over clays are sufficiently strong to provide good bearing the behaviour of the material en masse. The amount of capacity with low amounts of compression. Owing to low cement exerts a very significant control over the strength permeability, loading causes increases in pore water of a sandstone. A quartz cemented sandstone in which pressure which can take considerable periods of time, cement fills nearly all the void space may have a uniaxial perhaps years, to dissipate. Conversely, unloading pro- compressive strength exceeding 240 MN m -2 compared duces pore water suctions which also dissipate very with 3.5 MN m -2 for a poorly cemented sample. Follow- slowly. The stability of many excavations in overconsoli- ing tests carried out on a suite of Carboniferous sand- dated clays has been found to be controlled by pore water stones and siltstones Price (1960, 1963) concluded that pressures, failure often occurring some tens of years after increases in clay content at the expense of quartz has a excavation (Skempton & Hutchinson 1969). weakening effect. Furthermore, a mineral cemented rock The engineering behaviour of mudrocks can be greatly is stronger than one in which a matrix performs the same influenced by rock mass structures including fissures, function. sedimentary lamination due to the presence of bands of Unless poorly cemented and very porous, most sand- silt, shell fragments or other material and fissility induced stones provide adequate bearing capacity for most struc- by particle alignment. Measurements by Skempton et al. tures. Most well cemented, quartz-rich sandstones are (1969) indicated that the shear strength mobilized on reasonably durable although carbonate cements can be fissures can amount to little more than the residual value. subject to dissolution. Many sandstone sequences also However, the operational strength of overconsolidated contain beds of shale which may well exert a strong clay is less than the peak (intact) value but significantly control over the behaviour of the rock mass. Care must be higher than the fissure strength since in practice a failure taken to ensure that the weaker, more compressible shale surface will not be entirely co-planar with the fissures beds are not overstressed by loads imposed on the present. stronger sandstones. Where sequences of sandstone and Weathering has a profound effect on the engineering mudrock dip towards an excavation or valley, problems properties of overconsolidated clays in that the undrained with mass instability may occur due to translational shear strength may be reduced to less than half its sliding of the sandstone beds on the weak shale horizons. previous value. In addition, there are significant decreases Although it may be possible to excavate some porous, in effective shear strength and increases in compressibi- weak varieties of siltstone and sandstone without first lity. Due to the process of slaking many shales degrade fracturing the rock mass, in most cases this is not possible rapidly when exposed at the surface. Taylor & Spears in those formations of Palaeozoic or Precambrian age (1970) showed that the presence of expandable clay unless the rock is intersected by closely spaced disconti- minerals and lithological laminae significantly enhance nuities. On the other hand formations are generally self- the process. However, these authors also demonstrated supporting in excavations, although stability decreases that air breakage controls degradation. with time due to stress relief involving the opening up o~, Pyrite is a common constituent of many dark coloured and weathering along, discontinuities. Owing to their overconsolidated clays, mudrocks and coals. Its oxi- relatively high porosity and the presence of well deve- Downloaded from http://egsp.lyellcollection.org/ by guest on September 27, 2021

ASPECTS OF GEOLOGY IN PLANNING 7 loped joints many sandstone formations serve as aquifers. (1970) noted that when hydration occurs at shallow depth Thus significant water flows often ensue if such sand- some of the gypsum formed may be removed in solution, stones are intersected in excavations below the water leaving no net volume increase. table. Carbonaceous rocks including coals and lignite are the The most common carbonate rocks are limestone, fossilized remains of accumulations of plant debris. chalk and dolomite. The engineering properties of these Lignite is a soft brown material and although most coals rocks are strongly influenced by grain size and diagenetic are stronger, they vary from moderately weak to modera- processes involving cementation. Since the precipitation tely strong. of intergranular cements may occur very soon after deposition, the induration of carbonate rocks is not controlled by burial to the extent that it is in other Igneous and metamorphic rocks sedimentary rocks. In fact, because of early cementation carbonate rocks can retain high porosities even if deeply These rock types may be formed either by the cooling and buried. crystallization of magma or by the recrystallization of An important feature of carbonate rocks derives from existing rocks due to the action of heat and/or pressure. the fact that calcium carbonate may be dissolved by water Magma is generated within the mantle and crust of the rendered acidic by atmospheric carbon dioxide, organic Earth. Once solidified it forms a variety of igneous rocks. acids, industrial pollutants or mineral reactions, includ- The recrystallization of existing rocks may occur due to ing the oxidation of pyrite. The removal of rock from deep burial during mountain building processes which by along joints and bedding planes widens these discontinui- raising both the ambient pressure and temperature ties to the extent that open fissures or cave systems may be produces regionally metamorposed rock. Another situa- formed. In addition, if dissolution increases the porosity tion in which rocks become recrystallized arises if they are of the rock itself, its strength is reduced. close to a body of hot igneous rocks. Sinkholes, or dolines, develop where solution cavities Most varieties of unweathered and intact crystalline reach the surface. The consequences of the collapse of the rocks have high strength and low deformability and roofs of cavities, due either to natural causes or engineer- permeability. In fact most types are stronger and less ing works, must be given serious consideration when deformable than concrete so they provide excellent dealing with carbonate formations, particularly massive, conditions for foundations. On the other hand, in most pure ones. Frequently preferential dissolution along cases these rocks are impossible to excavate without first systems of vertical joints gives rise to a karstic formation fracturing the rock mass. and can be responsible for the formation of a highly Volcanic rocks of relatively recent age require careful irregular or pinnacled bedrock profile buried beneath investigation to ensure that they will provide adequate more recent deposits. Serious differential settlements, or bearing capacity. This is because lava flows are often laid even collapse, may then be the outcome of loading. in sequences which include weak ashes, weathered pro- Limestone beds are often interstratified with shales ducts and soils. Thus a heavy structure founded on a lava which may significantly modify the engineering beha- flow may overload an underlying weaker layer. viour of the rock mass. Strata which dip into the sides of Intrusions of granite may be adversely affected by excavations or valleys may be subject to translational hydrothermal alteration processes (hot aqueous solu- failure. tions) which result in the kaolinization of feldspar crystals Common types of evaporitic rocks include gypsum, within the rock. In extreme cases the rock is reduced to a anhydrite, halite (or rock salt) and potash. They are all mixture of quartz and mica crystals in a matrix of formed by direct precipitation of salts from water under kaolinite clay. Less severe hydrothermal alteration conditions of extreme evaporation. Of these examples reduces the strength and durability of the rock. anhydrite is the strongest and halite the weakest material. Weathering processes also cause the degradation of Evaporitic rocks exhibit varying degrees of non-elastic igneous rocks. Generally speaking the coarse-grained and deformation before failing. In fact, in halite the yield less quartz-rich varieties are the most susceptible to strength may be as little as one tenth of the ultimate weathering action. The process occurs much more rapidly uniaxial compressive strength of halite. Creep has been under humid or tropical climatic conditions where a mass recorded by Bell (1981) to account for between 20 and of clayey material containing relatively fresh core-stones 60% of the strain at failure in incremental loading tests on often mantles the underlying bedrock. Great care has to common evaporitic rocks. Halite is particularly prone to be taken to ensure that site investigation boreholes large scale creep deformation. intended to establish the depth of bedrock are not Gypsum, anhydrite, halite and potash all have higher terminated prematurely in large core-stones. In addition, solution rates than calcite so that flowing groundwater excavation and slope stability problems are a common can lead to the rapid development of solution features occurrence in weathered igneous material. (Eck & Redfield 1965; Bell 1975). Evaporitic minerals can The engineering properties of metamorphic rocks are be responsible for generating heave due to crystallization influenced both by the variety of rock metamorphosed pressures as precipitation takes place. In addition, anhy- and the type and grade of metamorphism. Intense contact drite theoretically can produce a volumetric expansion of or thermal metamorphism produces a suite of granular up to 63% during hydration into gypsum. However, in rocks most of which are very hard, impermeable, incom- practice, expansion is usually less than 12% and Holliday pressible and durable. Marble, quartzite and hornfels are Downloaded from http://egsp.lyellcollection.org/ by guest on September 27, 2021

F. G. BELL, J. C. CRIPPS, M. G. CULSHAW t~ M. O'HARA

the most common types. Like limestone, marble can be originated from deeply emplaced igneous intrusions. subject to dissolution in rainwater. Although weathering and alteration occur in the rock Due to recrystallization under conditions of high material, the processes responsible tend to concentrate directed stress, in regionally metamorphosed rocks, any along the discontinuities in rock masses. platy minerals, especially micas, display a preferred Several attempts have been made to devise an engineer- orientation. Thus rocks such as slate, phyllite, schist and ing classification of weathered rock. The problem can be gneiss are all rendered anisotropic in terms of their tackled in two ways. One method is to attempt to assess engineering behaviour; slate, in particular, splits into thin the grade of weathering by reference to some simple index sheets by virtue of this feature. Strength measurements test. Such methods provide a quantitative, rather than a carried out by Attewell & Sandford (1974) on samples of qualitative, answer. When coupled with a grading system, Penrhyn Slate indicated that samples in which the this means that the disadvantages inherent in these simple principal stress was either parallel to, or at right angles to, index tests are largely overcome. A second method of the cleavage plane were more than twice as strong as assessing the grade of weathering is based on a simple samples in which the direction was an intermediate one. description of the geological character of the rock Due to the large amount of mica, sometimes accompa- concerned as seen in the field, the description embodying nied by other weak minerals such as chlorite and talc, different grades of weathering which are related to some schists are weaker, less durable and somewhat more engineering performance (Table 1). deformable than other metamorphic rock types. Unless Obviously all grades of weathering may not be present gneisses contain large amounts of mica concentrated into in a given rock mass. Furthermore the classification of bands, these rocks have similar properties to granites. weathering grade may have to be modified to suit certain types of rock masses and other classifications have been advanced, for example, for chalk (Ward et al. 1968); and for marl (Chandler 1969). Weathering and alteration of rock masses Dearman (1974) maintained that an ideal classification Rock material tends to deteriorate in quality as a result of of weathering would provide an indication of the general weathering and/or alteration. Weathering refers to those engineering properties of the material concerned (irres- destructive processes, brought about by atmospheric pective of rock type). Usually the grades will lie one above agents at or near the Earth's surface, that produce a the other in a weathered profile developed from a single mantle of rock waste. Alteration refers to those changes rock type, the highest grade being at the surface. But this which occur in the chemical or mineralogical composition is not necessarily the case in complex geological condi- of a rock brought about by permeating hydrothermal tions. Even so the concept of grade of weathering can still fluids or by pneumatolytic action. Unlike weathering the be applied. Such a classification can be used to produce effects of alteration may extend to considerable depths maps and sections showing the distribution of the grade beneath the surface since the agents responsible may have of weathering at particular engineering sites.

TABLE 1. Classification of grade of weathering (after Anon 1981).

Degree of weathering Symbol (%) Term Description

Wo 0 Fresh No visible sign of material weathering Wl Less than 25 Slightly Discolouration indicates weathering of rock on major discontinuity surfaces W2 25-50 Moderately Less than half the rock material is decomposed and/or disintegrated to a soil. Fresh or discoloured rock is present either as a discontinuous framework or as corestones W3 50-75 Highly More than half the rock material is decomposed and/or disintegrated to a soil. Fresh or discoloured rock is present either as a discontinuous framework or as corestones W4 Over 75 Completely Majority of rock material is decomposed and/or disintegrated to soil. The original structure of the rock mass is still intact W5 100 Residual soil All material decomposed. No trace of rock structure preserved Downloaded from http://egsp.lyellcollection.org/ by guest on September 27, 2021

ASPECTS OF GEOLOGY IN PLANNING 9 Geological hazards national planning processes in order to avoid severe problems of economic and social dislocation. Unfortuna- Geological hazards can be responsible for devastating tely, however, development in many of these countries is large areas of the land surface and so can pose serious placing increasing numbers of people and property at risk constraints on development. However, geological pro- with, often, unplanned occupancy and use of marginal cesses such as volcanic eruptions, earthquakes, landslides and high risk zones. In particular, overcultivation and and floods cause disasters only when they impinge upon deforestation aggravate the problem. Indeed the asso- man or his activities. Nevertheless, both the number of ciated problems of soil erosion and excessive run-off have recorded disaster events, together with the number of not been confined to the developing world; for example, people killed is increasing each year. As an example of the such problems occurred in the United States in the 1930s. financial implications, Burton et al. (1978) estimated the The effects of a disaster may be lessened by reduction of cost of natural hazards ~ to be approximately $25 billion a vulnerability. Short-term forecasts a few days ahead of year for losses and $15 billion a year for costs involved in the event may be possible and complement relief and prevention and mitigation measures. They further esti- rehabilitation planning. In addition it is possible to mated that some 250 000 lives were lost annually. Geolo- reduce the risk of disaster by a combination of preventa- gical hazards pose formidable obstacles to economic tive and mitigative measures. To do this successfully, the growth, particularly in developing countries, and conse- patterns of behaviour of the geological phenomena quently preventative measures need to be included in posing the hazards need to be understood and the areas at

TABLE 2. Data required to reduce losses from geological hazards (after Hays & Shearer 1981).

Reduction decisions Technical information needed about the hazards from earthquakes, floods, ground failures, and volcanic eruptions

Avoidance Where has the hazard occurred in the past? Where is it occurring now? Where is it predicted to occur in the future? What is the frequency of occurrence? Land-use zoning Where has the hazard occurred in the past? Where is it occurring now? Where is it predicted to occur in the future?

What is the frequency of occurrence? What is the physical cause? What are the physical effects of the hazard? How do the physical effects vary within an area? What zoning within the area will lead to reduced losses to certain types of construction? Engineering design Where has the hazard occurred in the past? Where is it occurring now? Where is it predicted to occur in the future? What is the frequency of occurrence? What is the physical cause? What are the physical effects of the hazard? How do the physical effects vary within an area? What engineering design methods and techniques will improve the capability of the site and the structure to withstand the physical effects of a hazard in accordance with the level of acceptable risk? Distribution of losses Where has the hazard occurred in the past? Where is it occurring now? Where is it predicted to occur in the future? What is the frequency of occurrence? What is the physical cause? What are the physical effects of the hazard? How do the physical effects vary within an area? What zoning has been implemented in the area? What engineering design methods and techniques have been adopted in the area to improve the capability of the structure to withstand the physical effects of a hazard in accordance with the level of acceptable risk? What annual loss is expected in the area? What is the maximum probable annual loss?

1Natural hazards include hazards other than those associated with geology. Downloaded from http://egsp.lyellcollection.org/ by guest on September 27, 2021

10 F. G. BELL, J. C. CRIPPS, M. G. CULSHAW ~ M. O'HARA risk identified. Then, the level of potential risk may be crust. Major zones of volcanic activity lie beneath the decreased and the consequence of disastrous events central parts of the oceans and other, more minor ones, mitigated against by introducing regulatory measures or transect certain of the continental plates. For example, other inducements into the physical planning process. the oceanic rifts give rise to the volcanism which occurs in The impact of disasters may be reduced further by Iceland, Hawaii and many of the other ocean islands, and incorporating, into building codes and other regulations, volcanic activity is associated with the East African rift appropriate measures so that structures will withstand or system. Volcanism also occurs as a consequence of accommodate potentially devastating events. mountain building processes so that many currently Land-use planning for the prevention and mitigation of active volcanoes are situated in recently formed mountain geological hazards should be based on criteria establish- chains. Examples of volcanoes of this type include those ing the nature and degree of the risks present and their around the Pacific Ocean (Fig. 4) and the Mediterranean potential impact. Both the probable intensity and fre- Sea. quency of the hazard(s), and the susceptibility (or proba- The lava produced by a volcano varies according to the bility) of damage to human activities in the face of such geological situation so that although volcanic activity hazards are integral components of risk assessment. may take many forms, it is possible to distinguish two Vulnerability analyses comprising risk identification and main styles of activity. Generally speaking the activity evaluation should be carried out in order to make rational associated with the oceanic rift system entails the rela- decisions on how best the effects of potentially disastrous tively gentle upwelling of lava from fissure vents and some events can be reduced or overcome through systems of central cone type volcanoes. Since the lava has low permanent controls on land development. The geological viscosity, the eruptions tend to be non-violent in nature data needed in planning and decision making, as summar- although large quantities of ash and lava may be thrown ized by Hays & Shearer (1981), are given in Table 2. into the air (Fig. 5). Furthermore the lava may flow large distances before it cools. It contrast to this, the activity associated with recently formed mountain ranges tends to Volcanic activity be very explosive in nature. Owing to the high viscosity of Any assessment of the risk due to volcanic activity must the lava, volcanic vents can become blocked so that on the one hand take into account the consequences in subterranian pressures build up. The sudden release of terms of the number of lives at stake, the capital value of these pressures during an eruption can give rise to nue6s the property and the productive capacity of the area ardentes, localized seismicity and the ejection of large concerned, while on the other hand, the extent and type of quantities of material to great heights. Volcanoes of this hazard must also be considered. However, since volcanic type tend to attain a cone like form with short, inhomoge- eruptions, particularly large and potentially more harm- neous lava forms. ful ones, are rare events there may be insufficient Baker (1979) estimated that the active life span of most observational data on which to base reliable assessments volcanoes is probably between one and two million years. of the hazard. Since the activity frequently follows a broadly cyclical Volcanoes, and other manifestations of volcanic acti- pattern some benefit in terms of hazard assessment may vity, are variable in type, magnitude, duration and accrue from the determination of the recurrence interval significance as a hazard. Most volcanism is associated of particular types of eruption, the distribution of the with the system of rifts which are a feature of the Earth's resulting deposits, the magnitude of events and the

FIG. 4. Eruption of Mt St Helens in 1980, looking from the south FIG. 5. Eruption of ash from the Kirkefell volcano on the island (the only safe direction). (Courtesy of Robert Schuster, US of Heimaey, Iceland, in 1973. The ash entombed many houses. Geological Survey). (Courtesy of the Icelandic Embassy). Downloaded from http://egsp.lyellcollection.org/ by guest on September 27, 2021

ASPECTS OF GEOLOGY IN PLANNING l|

recognition of any short-term patterns of activity. For although windows may be broken several tens of kilo- instance, according to Booth (1979), four categories of metres away from major eruptions. hazard have been distinguished in Italy. As already stated, the detailed geological mapping of the products of volcanic eruption form an essential part of (i) Very high frequency events with mean recurrence the data required in the prediction of the magnitude, style intervals (MRI) of less than two years. The area and timing of volcanic activity. These investigations also affected by such events is usually less than 1 km 2. provide information regarding the hazards associated (ii) High frequency events with MRI values of 2-200 with eruptions. Thus hazard zoning entails the identifica- years. In this category damage may extend up to tion of areas liable to be adversely affected by particular 10 km 2. types of volcanic eruption during an episode of activity. (iii) Low frequency events with MRI values 200-2000 Examples of volcanic risk maps given by Booth (1979) years. Areal damage may cover over 1000 km 2. include expected ash fall depths, lava and pyroclastic (iv) Very low frequency events which are associated debris flow paths and the areal extent of lithic missile fall- with the most destructive eruptons and have out. Such maps are needed by local and national govern- MRI values in excess of 2000 years. The area ments so that appropriate land-uses, building codes and affected may be greater than 10 000 km 2. civil defence responses can be incorporated into planning procedures. It has been suggested by Fournier d'Albe The return periods of particular types of activity of (1979) that events with a mean recurrence interval of less individual volcanoes or centres of volcanic activity can be than 5000 years should be taken into account in the obtained by using the geological record to reconstruct production of maps of volcanic hazard zoning. He further past events. Used in conjunction with any available suggested that data on any events which have taken place historical records, these data form the bases of postula- in the last 50 000 years are probably significant. He tions of future events. However, it is unlikely that these proposed that two types of map would be useful for studies could ever be refined sufficiently for the time of economic and social planning. One would indicate areas activity to be predicted to within a decade. Furthermore, liable to suffer total destruction by lava flows, nue6s because it is unlikely that man will be capable of ardentes and lahars. The other would show areas likely to significantly influencing the degree of hazard, then the be affected temporarily by damaging, but not destructive reduction of risk can only be achieved by reducing phenomena including heavy falls of ash, toxic emissions exposure of life and property to volcanic hazards. and the pollution of surface or underground waters. Booth (1979) divided volcanic hazards into six categories, namely, premonitory earthquakes, pyroclast falls, pyroclast flows and surges, lava flows, structural collapse, and associated hazards. Each type represents a specific Earthquakes phase of activity during a major eruptive cycle of a Although some seismicity is caused by volcanic activity polygenetic volcano and may occur singly or in combina- most is due to movements along faults within the Earth's tion with other types. Damage resulting from volcano- crust. Another, more minor source of seismicity arises seismic activity is rare although intensities on the Mercalli from the release of stored strain energy within the crust by scale varying from VI to IX have been recorded over the activities of man. Areas of relatively high seismic limited areas. activity occur at the margins of tectonic crustal plates The likelihood of a given location being inundated with which due to earth processes move with respect to each lava during an eruption can be estimated from the other. Earthquakes are a manifestaton of this movement topographic constraints on the flow of the lava. The due to a build up of elastic strain within the rock mass on length of a lava flow is dependent upon the rate of either side of faults. Once the shearing stress exceeds the eruption, the viscosity of the lava and the topography of strength of the rock mass, movement occurs and elastic the area concerned. Given the rate of eruption it may be strain energy is released in the form of seismic waves. possible to estimate the length of new flows. Of course, it In most cases seismicity can be attributed to movement should be appreciated that each new eruption, as well as on a particular fault, or system of faults, rather than to the other surface processes, alter the topography of the slopes formation of a new fracture. However, the fault in of a volcano and therefore flow paths may change. What question may be along an ancient line of weakness within is more, prolonged eruptions of lava may eventually the rock mass, possibly lacking any surface expression. surmount obstacles which act as temporary dams so that Thus earthquakes may occur in areas remote from the lava invades areas which were formerly considered safe. margins of crustal plates, although these tend to be Hazards associated with volcanic activity also include relatively minor ones. destructive floods and mudflows caused by the sudden The hazards due to seismicity include the possibility of melting of snow and ice which cap high volcanoes, or by a structure being severed by fault displacement but a heavy downfalls of rain (vast quantities of steam may be much more likely event is damage due to shaking (Fig. 6). given off during an eruption), or the rapid collapse of a In addition, other hazards such as landslides, floods, crater lake. Far more dangerous are tsunamis generated subsidence and secondary earthquakes may be triggered by submarine explosive eruptions. Poisonous or asphix- by a seismic event. The destruction wrought by an iating gases are a further threat to life. Air blasts, shock earthquake depends on many factors. Of prime impor- waves and counter blasts are relatively minor hazards, tance are the magnitude of the event, its duration and the Downloaded from http://egsp.lyellcollection.org/ by guest on September 27, 2021

12 I:. G. BELL, J. C. CRIPPS, M. G. CULSHAW t~ M. O'HARA

duration of shaking is longer but the intensity of shaking is less, the higher frequency waves being attenuated more than the lower ones. The physical properties of the soils and rocks through which seismic waves travel, as well as the geological structure, also influence the effects of an earthquake. Although according to Ambraseys (1974) the maximum acceleration generated by an earthquake in competent rock is about 2 • gravity (2 g) the ability of other geological formations to transmit the vibrations varies. For instance, alluvial deposits are only capable of transmitting accelerations in the range 0.1 g to 0.6 g depending on the type of material. However, the amplitude of seismic waves increases as they pass from competent rocks into less competent ones. Non-rigid structures founded on alluvial deposits are particularly FIG. 6. Intact blocks of flats which have foundered into liquefied vulnerable to the effects of seismic shaking for this reason. ground during the Niigata, Japan, earthquake, 1964. Ground vibrations often lead to the consolidation of cohesionless soils and associated settlement of the ground surface. Loosely packed saturated sands and silts tend to response of buildings and other elements of the infra- liquify, thus losing their bearing capacity, becoming structure. unstable in slopes and undergoing consolidation. The strengths of earthquakes may be expressed in terms Details about the occurrence, magnitude and effects of of intensity or magnitude. Earthquake intensity scales are earthquakes through time can be obtained by carrying a qualitative expression of the damage caused by an event. out long term seismic monitoring. In the absence of The most widely accepted intensity grading is the Mercalli suitable instrumental data the seismic history of an area scale given in Table 3 (Wood & Neumann 1931). This was may be established by interpreting historical accounts, slightly modified by Richter (1956). and archaeological and geological observations. For The magnitude of an earthquake is an instrumentally instance, Davenport (1987) described how disturbance to measured expression of the energy liberated during the recent sediments has been used to indicate both the timing event. Richter (1935) devised a scale in which the and magnitude of seismic events in Scotland. maximum amplitude of the resulting seismic waves are Maps can be drawn (Fig. 7) by using the seismic history expressed on a logarithmic scale from 1 to 10. An of an area, which indicate the epicentral areas of earth- earthquake of magnitude 2 is the smallest likely to be felt quakes and these are zoned according to temporal activity by humans and earthquakes of magnitude 5 or less are and magnitude. Medvedev (1968) proposed that the unlikely to cause damage to well constructed buildings. seismic zoning of a region should be based upon a study of The maximum magnitude of earthquakes is limited by the the earthquakes which occur there, an investigation of the amount of strain energy which the rock mass can sustain laws governing the occurrence of earthquakes of different before failure occurs, hence the largest tremors have had a intensity, an analysis of the geological conditions under magnitude of 8.9. Such events cause severe damage over a which earthquakes occur and the investigation of special wide area. The magnitude of an earthquake event depends on the length of the fault which ruptures and the amount of displacement which occurs. Generally speaking movement only occurs on a limited length of a fault during one event. A magnitude 7 earthquake would be produced if a 150 km length of a fault underwent a displacement of about 1.0 m. By contrast, some faults continuously creep allowing an accumulative displacement of several centi- metres per year without major shocks. Many seismologists believe that the duration of an earthquake is the most important factor as far as damage or failure of structures, soils and slopes are concerned. What is important in hazard assessment is the prediction of the duration of seismic shaking above a critical ground acceleration threshold. The magnitute of an earthquake affects the duration much more than it affects the maximum acceleration, since the larger the magnitude the greater the length of ruptured fault. Hence the more extended the area from which the seismic waves are FIG. 7. Probabilistic representation of seismic hazard in the USA. emitted. With increasing distance from the fault the (After Algermissen & Perkins 1976). Downloaded from http://egsp.lyellcollection.org/ by guest on September 27, 2021

ASPECTS OF GEOLOGY IN PLANNING 13

TABLE 3. Modified Mercalli scale (1956 version) with Cancani's equivalent acceleration.

Acceleration* Degrees Description mm s- 2

I Not felt. Only detected by seismographs Less than 2.5 II Feeble. Felt by persons at rest, on upper floors, or favourably placed. 2.5 to 5.0 III Slightly felt indoors. Hanging objects swing. Vibration like passing of 5.0 to 10 light trucks. Duration estimated. May not be recognised as earthquake. IV Moderate. Hanging objects swing. Vibration like passing of heavy 10 to 25 trucks, or sensation or a jolt like a heavy ball striking the walls. Standing motor cars rock. Windows, dishes, doors rattle. Glasses clink. Crockery clashes. In the upper range of IV wooden walls and frame creak. Rather strong. Felt outdoors, direction estimated. Sleepers wakened. 25 to 50 Liquids disturbed, some spilled. Small unstable objects displaced or upset. Doors swing, close, open. Shutters and picture move. Pendulum clocks stop, start, change rate. VI Strong. Felt by all. Many frightened and run outdoors. Persons walk 50 to 100 unsteadily. Windows, dishes, glassware broken. Ornaments, books, etc, fall off shelves. Pictures fall off walls. Furniture moved or overturned. Weak plaster and masonry cracked. Small bells ring (church, school). Trees, bushes shaken visibly or heard to rustle. VII Very strong. Difficult to stand. Noticed by drivers of motor cars. 100 to 250 Hanging objects quiver. Furniture broken. Damage to masonry D, including cracks. Weak chimneys broken at roof line. Fall of plaster, loose bricks, stones, tiles, cornices, also unbraced parapets and architectural ornaments. Some cracks in masonry C. Waves on ponds, water turbid with mud. Small slides and caving in along sand or gravel banks. Large bells ring. Concrete irrigation ditches damaged. VIII Destructive. Steering of motor cars affected. Damage to masonry C, 250 to 500 partial collapse. Some damage to masonry B, none to masonry A. Fall of stucco and some masonry walls. Twisting, fall of chimneys, factory stacks, monuments, towers, elevated tanks. Frame houses moved on foundations if not bolted down, loose panel walls thrown out. Decayed piling broken off. Branches broken from trees. Changes in flow or temperature of springs and wells. Cracks in wet ground and on steep slopes. IX Ruinous. General panic. Masonry D destroyed, masonry C heavily 500 to 1000 damaged, sometimes with complete collapse, masonry B seriously damaged. General damage to foundations. Frame structures, if not bolted, shifted off foundations. Frames cracked, serious damage to reservoirs. Underground pipes broken. Conspicuous cracks in ground. In alluviated areas sand and mud ejected, earthquake fountains, sand craters. Disastrous. Most masonry and frame structures destroyed with their 1000 to 2500 foundations. Some well built wooden structures and bridges destroyed. Serious damage to dams, dykes, embankments. Large landslides. Water thrown on banks of canals, rivers, lakes, etc. Sand and mud shifted horizontally on beaches and flat land. Rails bent slightly. XI Very disastrous. Rails bent greatly. Underground pipelines completely 2500 to 5000 out of service. XII Catastrophic. Damage nearly total. Large rock masses displaced. Over 5000 Lines of sight and level distorted. Objects thrown into the air.

* These are not peak accelerations as instrumentally recorded.

features accompanying the occurrence of earthquakes. and intensity, and information concerning attenuation of The production of maps of seismic zoning in the Soviet intensity with distance. Union therefore takes account of the depth of earthquake Specific conditions in each seismic region, peculiarities foci, the relationship between energy at the focus and of the seismic regime, different forms ofseismo-geological epicentral intensity, the correlation between magnitude linking and the extent to which the area has been studied, Downloaded from http://egsp.lyellcollection.org/ by guest on September 27, 2021

14 F. G. BELL, J. C. CRIPPS, M. G. CULSHAW t~ M. O'HARA mean that there can be no rigorous standard way of using Hutchinson (1969) noted that falls in clay soils generally the seismic data for zoning all regions. Furthermore, in represented short-term failures, which originated from a the compilation of these maps, all engineering data tension crack, in newly exposed slopes, for example, those concerning the surface manifestations of earthquakes subject to active erosion. should refer to identical ground conditions. Geological In true slides, the movement results from shear failure investigations may be used to establish the seismic history along one or several surfaces, such surfaces offering the of an area, since differing seismic responses of geological least resistance to movement. The mass involved may or materials allow the prediction of the effects of an may not experience deformation. One of the most earthquake and identify areas in which crustal strain is common types is the rotational slide in which the slip building up. However, geological data provide only a surface is approximately spoon-shaped. Such slides qualitative assessment of seismic risk. To obtain a usually develop in clay slopes and they are commonly quantitative expression the geological data must be deep seated (0.15 < depth/length < 0.33). When the back examined in conjunction with the seismic response of scar at the head of a rotational slide is almost vertical and particular engineering structures and seismic data. unsupported, then further failure usually occurs after a period of time (Fig. 8). As a consequence successive rotational slides develop until a stable condition is Landslides and slope movements established. These are retrogressive slides (Fig. 9) and Movements of slopes can range in magnitude from soil they develop in a headward direction. These slides have a creep on the one hand to instantaneous and colossal common basal shear surface along which the individual landslides on the other. Creep is a more or less continuous planes of a failure are combined. process, which is a distinctly surface phenomenon and Translational slides occur in inclined stratified deposits occurs on slopes with gradients somewhat in excess of the or formations in which a discontinuity slopes towards a angle of repose of the material involved. Evidence of soil valley or excavation. The movement occurs along this creep may be found on many soil-covered slopes. For example, it occurs in the form of small terracettes, downslope tilting of poles, the curving downslope of trees and soil accumulation on the uphill sides, of walls. Solifluction is a form of creep which occurs in cold climates or high altitudes where masses of saturated rock waste move downslope on a surface of sliding at some depth below ground level. Varnes (1958) defined landslides as the downward and outward movement of slope-forming materials composed of rocks, soils, or artificial fills. Creep is excluded from this definition. Movement may take place by falling, sliding or flowing, or some combination of these processes. Obviously sliding or flowing movements involve the development of a slip surface between the separating and remaining masses. Landslides occur because the forces creating movement, the disturbing forces (MD) exceed the resisting forces (MR). In general terms the stability of a slope may be defined by a factor of safety (F) where F = MR/MD ( 1 ) If the factor of safety exceeds one, then the slope should be stable, whereas if it is less than one, the slope is unstable. Most of the force causing movement is due to the self-weight of the moving material although, in some cases applied loads cause additional destabilization. Forces resisting movement include the shear resistance mobilized by the material. The latter is reduced by increasing pore water pressure. Falls are a very common style of slope failure. The moving mass travels mostly through the air by free fall, by saltation or by rolling, with little or no interaction between the moving fragments. Movements are very FIG. 8. Frequent landsliding at different times along different rapid and may not be preceded by minor movements. In shear surfaces have been responsible for the destruction of the rockfalls the fragments are of various sizes and are A625 at Mam Tor, near Castleton, Derbyshire. No further generally broken in the fall. They accumulate at the attempts are contemplated to repair and restore the road because bottom of a slope as a scree deposit. Skempton & of cost and the likelihood of future movements. Downloaded from http://egsp.lyellcollection.org/ by guest on September 27, 2021

ASPECTS OF GEOLOGY IN PLANNING 15

and the resistance along it is less than the driving force, whereas rotational sliding usually brings equilibrium to an unstable mass. Slab slides can occur on gentler surfaces than rotational slides and may be more extensive in areal extent. In flow slides the movement resembles that of a viscous fluid. Slip surfaces are usually not visible or are short lived and the boundary between the flow and the material over which it moves may be sharp or may be represented by a zone of plastic flow. Usually the flowing material has a high water content. Because most landslides occur in areas previously affected by instability and because few occur without prior warning, Cotecchia (1978) emphasized the importance of carrying out careful surveys of areas which appear potentially unstable by making systematic records of relevant phenomena. He provided a review of the FIG. 9. Retrogressive landslides in Pleistocene deposits, Filey techniques involved in mapping mass movements, as well Bay, Yorkshire. as itemizing which data should be included on such maps. He maintained that the ultimate aim should be the discontinuity, frequently a bedding plane. The mass production of maps of landslide hazard zoning (Fig. 10). involved in the movement becomes dislodged because the A useful starting point in landslide investigations is a force of gravity overcomes the frictional resistance along checklist of the type suggested by Cooke & Doornkamp the potential slip surface, the mass having been detached (1974). Each separate slope unit can be classified accord- from the parent rock along a prominent discontinuity ing to a stability rating and, furthermore, it provides for such as a major joint. Slab slides, in which the slip surface systematic examination of the main factors influencing is roughly parallel with the ground surface, are a common mass movement. The value of aerial photographs, precise type of translational slide. Such a slide may progress surveying and geophysical methods in landslide investiga- almost indefinitely if the slip surface is sufficiently inclined tion have been discussed by Yague (1978).

FIG. 10. An example of engineering geological mapping in terms of landslide hazard in the Crested Butte-Gunnison area. (After Soule 1980) Downloaded from http://egsp.lyellcollection.org/ by guest on September 27, 2021

16 F. G. BELL, J. C. CRIPPS, M. G. CULSHAW t~ M. O'HARA

Huma & Radulescu (1978) described the use of a computer to produce maps of slope stability. The necessary data were obtained from aerial photographs as well as field and laboratory investigations. They included a survey of the lithology and mechanical characteristics of the rocks concerned, their structural and hydrogeological conditions, slope angle, amount of vegetation cover and exposure. A computer was then used to assess the data in terms of slope stability and to plot a map of land stability zones. Landslide prevention can be achieved by reducing the effect of the activating forces, by increasing the forces resisting movement or by avoiding or eliminating the slide. Partial removal of potentially unstable material, reduction of slope angle, or benching may be used to reduce the self-weight of the slope which is the principal motivating force. However, these methods are not always applicable. Various restraining structures such as retaining walls, cribs, gabions, buttresses and rock bolts may be used to strengthen a slope and so increase its resistance to movement. Drainage of a slope, both internal and surface, represents the most generally applicable preventative and corrective means of dealing with movements of slopes (Figs 1 l a and b).

River action and flooding All natural rivers form part of a drainage system, the form of which is influenced by rock type and structure, the nature of the vegetation cover and the climate. An understanding of the processes which underlie river development forms the basis of proper river management. Rivers form part of the hydrological cycle in that they carry precipitation run-off. This run-off is the surface water which remains after evapotranspiration and infiltration into the ground. Some precipitation may be frozen, only to contribute to run-off at some later time, while any precipitation that has soaked into the ground may reappear as springs where the water table meets the ground surface. Although, due to heavy rainfall or in areas with few channels, the run-offmay occur as a sheet, generally speaking it becomes concentrated into channels. These become eroded by the flow of water so that they form continuous valleys. The amount of erosion accomplished by a river in a given time depends upon the energy it possesses, this, in turn, is influenced by its volume, flow velocity and the character and particle size of its load. In steep terrain where flow velocities are rapid, erosion forms steep sided valleys. Bank recession permits FIG. 1 I. (a) Internal drainage gallery in restored and stabilized the stream to attack the downstream side of the eroded slope at Aberfan, South Wales. (b) Surface drainage in a slope in weathered granite, Hong Kong. area with an accompanying deposition of material on the inside of the resulting bend. Thus a meander develops. Meanders may migrate both laterally and downstream, meanders. Thus the continual migration of meanders where their amplitude is progressively increased. In this slowly reduces the valley floor to an almost flat plain manner spurs are continually eroded, first becoming more which slopes gently downstream and is bounded by asymmetrical until they are eventually truncated. The shallow valley sides. slow deposition which occurs on the convex side of a The alluvial flood plain may comprise many kinds of meander will, as lateral migration proceeds, produce a deposits, laid down both in the channel and outside it. gentle sloping area of alluvial ground called the flood Vertical accretion of a flood plain is accomplished by in- plain. The flood plain gradually grows wider as the river channel filling and the growth of overbank deposits bluffs recede until it is as broad as the amplitude of the during and immediately after floods. Gravel and coarse Downloaded from http://egsp.lyellcollection.org/ by guest on September 27, 2021

ASPECTS OF GEOLOGY IN PLANNING 17

probability of the size of the discharge that could be expected during any given time interval. The quantity of flow in rivers can be estimated from measurements of their cross-sectional areas and, current speed. Generally channels become wider relative to their depth and adjust to larger flows with increasing distance downstream. Bankfull discharges also increase downstream in proportion to the square of the width of the channel or of the length of individual meanders, and in proportion to the 0.75 power of the total drainage area focused at the point in question. The lower stage of a river, in particular, can be divided into a series of hazard zones based on flood stages and risk. Obviously a flood plain management plan involves the determination of such zones. These are based on the historical evidence related to flooding which includes the FIG. 12. Damage on the outskirts of Lynmouth, Devon, magnitude of each flood and the elevation it reached as following the floods of 1952. (Courtesy of the British Geological Survey; photographic collection no. A8716) well as the recurrence intervals; the amount of damage involved; the effects of urbanization and any further development; and an engineering assessment of flood sands are moved chiefly at flood stages and deposited in potential. Maps then are produced from such investiga- the deeper parts of a river. When the river overtops its tions which, for example, show the zones of most frequent banks during flood, its ability to transport material is flooding and the elevation of the flood waters. lessened so that coarser particles are deposited near the Flood plain zones can be designated for specific types banks to form levees. These stand above the general level of land use. For instance, in the channel zone water of the adjoining plain so that the latter is usually poorly should be allowed to flow freely without obstruction (for drained and marshy. This is particularly the case when example, bridges should allow sufficient waterway capa- levees divert the course of tributaries. Finer material is city). Another zone could consist of that area with carried further and laid down as backswamp deposits. At recurrence intervals of 1 to 20 years which could be used this point a river sometimes aggrades its bed, eventually for agricultural and recreational purposes. Buildings raising it above the level of the surrounding land. If levees would be allowed in the zone encompassing the 20 to 100 become breached by flood waters, very large areas may be year recurrence interval, but they would have to have inundated. some form of protection against flooding. In the United Floods represent the commonest type of geological States, communities that are affected by flooding are hazard. They probably affect more individuals and their obliged to adopt flood plain management measures which property (Fig. 12) than all the other hazards put together. involve adequate land use and control methods to meet However, the likelihood of flooding is more predictable minimum safety criteria for protection against a 100 year than some other types of hazards such as earthquakes, flood (that is, a flood with a magnitude which occurs on volcanic eruptions and landslides. Most disastrous floods average once every 100 years). are the result of excessive precipitation or snowmelt, that Flood protection measures include methods of confin- is, they are due to excessive surface run-off. It usually ing the flood within with the river channel by constructing takes some time to accumulate enough run-off to cause a embankments and training walls which heighten and major disaster. This lag time is an important parameter in strengthen the banks; stage reduction which involves flood forecasting. Flash floods prove the exception. In strengthening or deepening a river channel; diversion of most regions floods occur more frequently in certain part of the river water via a relief channel; and attempts to seasons than others. regulate flows by the use of sluice gates or dams with Rivers may be considered in flood when their level has impounding reservoirs. risen to an extent that damage occurs. The physical Control of the higher stretches of a river in those characteristics of a river basin together with those of the regions prone to soil removal by gullying and sheet stream channel affect the rate at which discharge down- erosion is very important. The rapid removal of the soil stream occurs and so calculations of the lag time is a mantle means that run-off becomes increasingly more complicated matter. Nonetheless, once enough data on rapid and consequently the problem of flooding is rainfall and run-off versus time have been obtained and aggravated. These problems were tackled in the Tennes- analysed an estimate of where and when flooding will see Valley by establishing a well planned system of occur along a river system can be made. Analyses of agriculture so that soil fertility was restored and main- discharge are related to the recurrence interval to produce tained, and the valley slopes were reforested. Gullies were a flood frequency curve. The recurrence interval is the filled and small dams were constructed across the head- period of years within which a flood of a given magnitude streams of valleys to regulate run-off. Larger dams were or greater occurs and is determined from field measure- erected across tributary streams to form catchment basins ments at a gauging centre. It applies to that station only. for flood waters. Finally, large dams were build across the The flood frequency curve can be used to determine the main river to smooth flood flow (Lilienthal 1944). Downloaded from http://egsp.lyellcollection.org/ by guest on September 27, 2021

18 F. G. BELL, J. C. CRIPPS, M. G. CULSHAW t~ M. O'HARA

Marine action Waves, acting on beach material, are a varying force. They vary with time and place due to, first, changes in wind force and direction over a wide area of sea, and second, changes in coastal aspects and offshore relief. This variability means that the beach is rarely in equilibrium with the waves, in spite of the fact that it may only take a few hours for equilibrium to be attained under new conditions. Such a more or less constant state of disequili- brium occurs most frequently where the tidal range is considerable, as waves are continually acting at a different level on the beach. Tides may play an important part in beach processes. In particular, the tidal range is responsible for the area of the foreshore over which waves are active. Tidal streams are especially important where a residual movement resulting from differences between ebb and flood occurs, FIG. 13. Marine erosion of a Boulder Clay cliff at Skipsea Sands, and where there is abundant loose sediment for the tidal Holderness, Yorkshire, leading to the destruction of holiday cottages. (Courtesy of Alan Forster, British Geological Survey). streams to transport. They are frequently fast enough to carry coarse sediment but the forms, notably bars, normally associated with tidal streams in the offshore zone or in tidal estuaries usually consist of sand. These The degree to which rocks are traversed by discontinui- features, therefore, only occur where sufficient sand is ties affects the rate at which they are removed by marine available. In quieter areas where the tide ebbs and floods erosion. In particular the attitude of joints and bedding over large flat expanses depositing muddy material, tidal planes is important. Where the bedding planes are vertical mud flats and salt marshes are developed. Mud also or dip inland, then the cliff recedes vertically under marine accumulates in runnels landward of high ridges, in attack. But if beds dip seawards blocks of rock are more lagoons and on the lower foreshore where shelter is readily dislodged since the removal of material from the provided by offshore banks. High spring tides during base of the cliff means that the rock above lacks support winter months frequently have been responsible for and tends to slide into the sea. Marine erosion is also extensive marine inundation of low lying lands bordering concentrated along fault planes. the North Sea. The height of a cliff is another factor which influences Coasts undergoing erosion display two basic elements the rate at which coastal erosion takes place. The higher of the coastal profile, namely, the cliff and the bench or the cliff the more material falls when its base is under- platform. As erosion continues the cliffincreases in height mined. This in turn means that a greater amount of debris and the bench widens. The nature of the impact of a wave has to be broken down and removed before the cliff is upon a coastline depends to some extent on the depth of once more attacked with the same vigour. the water and partly on the size of the wave. The vigour of Dunes are formed by onshore winds carrying sand- marine action drops sharply with increasing depth from sized material landward from the beach along low-lying the water surface. Although large waves may throw stretches of coast where there is an abundance of sand on material above the high-water level and thus act as the foreshore. Leatherman (1979) maintained that dunes constructive agents, they nevertheless have an overall act as barriers, energy dissipators and sand reservoirs tendency to erode the beach whilst small waves are during storm conditions. For example, the broad sandy constructive. When steep storm waves attack a sand beaches and high dunes along the coast of the Nether- beach they are usually entirely destructive and the coarser lands present a natural defence against inundation during the sand, the greater the quantity which is removed. It is storm surges. Because dunes provide a natural defence by no means a rarity for the whole beach to be removed by against erosion, once they are breached the ensuing storm waves. coastal changes may be long-lasting. The rate at which coastal erosion proceeds is influenced In spite of the fact that dunes inhibit erosion, Leather- by the nature of the coast itself and is most rapid where man (1979) stressed that without beach nourishment they the sea attacks soft unconsolidated sediments (Fig. 13). cannot be relied upon to provide protection, in the long When soft deposits are being actively eroded the cliff term, along rapidly eroding shorelines. Beach nourish- displays signs of landsliding together with evidence of ment widens the beach and maintains the proper func- scouring at its base. For erosion to continue the debris tioning of the beach-dune system during normal and produced must be removed by the sea. This is usually storm conditions. accomplished by longshore drift. If on the other hand When waves move parallel to the coast they simply material is deposited to form extensive beaches and the move sand and shingle up and down the beach. On the detritus is reduced to a minimum size, then the submarine other hand when they approach the coast at an angle slope becomes very wide. Wave energy is dissipated as the material is moved up the beach by the swash in the water moves over such beaches and cliff erosion ceases. direction normal to that of wave approach and then it is Downloaded from http://egsp.lyellcollection.org/ by guest on September 27, 2021

ASPECTS OF GEOLOGY IN PLANNING 19 rolled down the steepest slope of the beach by the able, increase in the beach width around the mouths of backwash. Consequently material is moved in a zig-zag rivers. path along the beach. This accumulative movement is Groynes are frequently used to stabilize beaches by known as longshore drift, a process which transports arresting, or controlling, longshore drift. They are usually beach material appreciable distances along coasts. The constructed at right angles to the shore and should be duration of movement along a coastline is dependent approximately 50% longer than the beach on which they upon the direction of the dominant winds. An indication are erected. However, as groynes reduce the amount of of the direction of longshore drift is provided by the material passing downdrift, they can prove detrimental to orientation of spits along a coast. downdrift benches. Hence, beach nourishment is becom- The amount of longshore drift also is influenced by ing a more common method of erosion control since it is coastal outline and wave length. Short waves can usually the only form of control protection which does approach the shore at a considerable angle, and generate not adversely affect other sectors of the coast. consistent downwave currents. This is particularly the Seawalls range from a deposit of rip-rap to a masonry case on straight or gently curving shores and can result in or concrete retaining wall. Bulkheads are vertical walls of serious erosion where the supply of beach material timber or steel sheet piling. Walls not only provide reaching the coast from updrift is inadequate. Conversely protection against marine erosion, they also afford long waves suffer appreciable refraction before they reach protection against marine inundation. the coast. Tsunamis are large masses of water which affect coastal Before any project affecting a coastal area can be regions and can cause widespread marine inundation. started, a complete study of the beach system should be Most tsunamis are associated with earthquakes which made. In particular, the selection of any erosion remedial originate in the ocean floor though they may also be measures necessitates consideration of whether the beach caused by volcanic activity and submarine landslides. As conditions represent a long-term trend or whether they the tsunami waves approach the coast they slow down are cyclical phenomena which may recur at some time in and increase in height, moving onshore as highly destruc- the future. The preliminary investigation of the area tive breakers. Waves have been recorded up to nearly concerned should first consider the landforms and rock 20 m in height above normal sea level. Large waves are formations along the beach and adjacent rivers, giving most likely to occur where tsunamis move into narrowing particular attention to their durability and stability. The inlets. The Pacific Tsunami Warning System (PTWS) is a rates of erosion and the proportion of eroded material communications network covering all the countries bor- contributing to the beach also must be estimated. dering that ocean and is designed to give advance warning The behaviour of unconsolidated materials when of dangerous tsunamis. However, it cannot provide a weathered, together with their slope stability and likeli- warning of an impending tsunami to those areas close to hood of sliding has to be taken into account. Consider- its point of origin. Evacuation of an area depends on ation must be given to the width, slope, composition and estimating just how destructive a tsunami will be when it state of erosion or accretion of the beach, the presence of arrives on a particular coast. bluffs, dunes, marshy areas or vegetation in the backshore Breakwaters, revetments, seawalls and other structures area, the rock formations which compose the headlands may offer some protection against tsunamis. Design and the presence of beach structures such as groynes. against tsunami damage involves raising buildings off the Samples of the beach and underwater material have to be ground and erecting shear walls normal to the direction of collected and analysed for such factors as their particle the wave front. Reinforced concrete structures having size distribution and mineral content. Mechanical analy- adequate foundations do not usually suffer noticeable ses may prove useful in helping to determine the amount damage. of material which is likely to remain on the beach, for beach sand is seldom finer than 0.1 mm in diameter. The Wind action amount of material moving along the shore should be investigated for the effectiveness of any corrective struc- In arid regions, in particular, because there is little tures erected may depend upon the quantity of drift vegetation, wind action is much more significant than available. elsewhere. By itself, wind can only remove uncemented Topographic and hydrographic surveys of an area rock debris but once armed with rock particles, the wind allow the compilation of maps and charts from which a becomes a noteworthy agent of abrasion. study of the changes along the coast may be made. One of the most important factors in wind erosion is its Observations are taken of winds, waves and currents and velocity. Its turbulence, duration and direction are also information is gathered on streams which enter the sea in important. As far as the mobility of particles is concerned or near the area concerned. Inlets across a beach need the important factors are their size, shape and density. It particular evaluation. For instance, although during would appear that particles less than 0.1 mm in diameter normal times there may be relatively little longshore drift, are usually transported in suspension, those between 0.1 if upbeach breakthroughs occur in a bar off an inlet and 0.5 mm are normally transported in saltation and mouth, then sand is moved downbeach and is subjected to those larger than 0.5 mm tend to be moved by traction or longshore drift. The contributions made by large streams creep. Grains with a relative density of 2.65, such as may vary. For example, material brought down by large quartz sand, are most susceptible to wind erosion in the floods may cause a temporary, but nevertheless appreci- size range 0.1 to 0.15 mm. A wind blowing at 12 km per Downloaded from http://egsp.lyellcollection.org/ by guest on September 27, 2021

20 F.G. BELL, J. C. CRIPPS, M. G. CULSHAW ~ M. O'HARA hour will initiate movement of grains of 0.2 mm diameter; by society of which domestic waste, hazardous waste and a lesser velocity will keep the grains moving. Binding radioactive waste are probably the most important. agents, such as silt, clay and organic matter, hold particles At the present time, increasing concern is being together and so impede wind erosion. Soil moisture also expressed over the disposal of domestic waste products. contributes to cohesion between particles and vegetation Although domestic waste is disposed of in a number of affords surface cover and increases surface roughness ways, quantitatively the most important method is place- which, in turn, reduces the velocity of wind immediately ment in a sanitary landfill. For example, in the United above it. Kingdom, of the approximately 18.6 million tonnes of Several factors control the form which an accumu- domestic solid waste produced each year about 76% is lation of sand adopts. These include the rate at which disposed of in landfills. sand is supplied; wind speed, frequency and constancy of Leachate is formed when rainfall infiltrates a landfill direction; size and shape of the sand grains; and the and dissolves the soluble fraction of the waste, and from nature of the surface across which the sand is moved. It is the soluble products formed as a result of the chemical commonly believed that sand dunes come into being and biochemical processes occurring within the decaying where some obstacle prevents the free flow of sand, sand wastes. Generally, the conditions within a landfill are piling up on the windward side of the obstacle to form a anaerobic, so leachates often contain high concentrations dune. However, in areas where there is an exceptionally of dissolved organic substances. Barber (1982) estimated low rainfall and therefore little vegetation to impede the that a small landfill site with an area of 1 hectare located in movement of sand, observation has revealed that dunes southern England could produce up to 8 m 3 of leachate develop most readily on fiat surfaces, devoid of large per day. A site with an area ten times as large would obstacles. It would seem that where the size of the sand produce a volume of effluent with approximately the same grains varies or where a rocky surface is covered with Biological Oxygen Demand (BOD) per year as that of a pebbles, dunes grow over areas of greater width than 5 m. small rural sewage treatment works. Hence the location Such patches exert a frictional drag on the wind causing and management of these sites must be carefully con- eddies to blow sand towards them. Sand is trapped trolled. Clearly, the production of leachate may represent between the larger grains or pebbles and an accumulation a health hazard, for example, by contaminating a ground- results. Hazard maps, such as that in Fig. 14, showing water supply which would then require costly treatment unstable sand dunes and their migration have been prior to use. Furthermore, since it can also threaten the produced for development purposes in arid regions surface water resource potential of a region an economic (Cooke et al. I978). problem of considerable magnitude may be created. Barber (1982) identified three classes of landfill site based upon hydrogeological criteria (Table 4). When Geological related hazards induced by man assessing the suitability of a site, two of the principal considerations are the ease with which the pollutant can Waste disposal be transmitted through the substrata and the distance it is likely to spread from the site. Consequently, the primary Waste disposal is one of the most expensive environmen- and secondary permeability of the formations underlying tal problems. Many types of waste material are produced the landfill area are of major importance. It is unlikely

FIG. 14. Geomorphological analysis of a proposed airport site in Dubai with respect to the threat from mobile sand dunes. (After Cooke et al. 1978). Downloaded from http://egsp.lyellcollection.org/ by guest on September 27, 2021

ASPECTS OF GEOLOGY IN PLANNING 21

TABLE 4. Classification of landfill sites based upon their hydrogeology (after Barber 1982).

Designation Description Hydrogeology

Fissured site, or site with rapid Material with well developed Rapid movement of leachate via subsurface liquid flow secondary permeability features fissures, joints, or through coarse sediments. Possibility of little dispersion in the groundwater, or attenuation of pollutants. Natural dilution, dispersion and Permeable materials with little Slow movement of leachate into attenuation of leachate or no significant secondary per- the ground through an unsatur- meability ated zone. Dispersion of leachate in the groundwater, attenuation of pollutants (sorption, biodegradation, etc.) probable. Containment of leachate Impermeable deposits such as Little vertical movement of lea- clays or shales, or sites lined chate. Saturated conditions ex- with impermeable materials or ist within the base of the landfill membranes

that a landfill licence would be granted to a site of the type Gray et al. (1974) recommended that at dry sites, tipping listed first in Table 4. There also would be grounds for an should take place on granular material which has a objection to a landfill site falling within the second thickness of 15 m or more, while any water wells should category of Table 4 if the site was located within the area be located at least 0.8 km away. of diversion to a water supply well. Generally, the third When sites have to cope with liquid or industrial category in which the leachate is contained within the wastes, or wastes of indeterminate composition, the landfill area, is to be preferred. Since all natural materials danger is increased. Chemical and biochemical hazardous possess some degree of permeability, total containment wastes include those which are toxic, infectious, corrosive can only be achieved if an artificial impermeable lining is and/or ignitable. Obviously their uncontrolled dumping provided over the bottom of the site. However, there is no can pollute or contaminate soil and groundwater guarantee that clay, soil cement, asphalt or plastic lining resources. One of the classic problems associated with the will remain impermeable permanently. Thus, the migra- disposal of chemical waste occurred at the town of tion of materials from the landfill site into the substrata Niagara in New York State where toxic chemical waste will occur eventually, although the length of time before was dumped in an excavation which had been intended this happens may be subject to uncertainty. In some for a canal, the notorious 'Love Canal', and buried. This instances the delay will be sufficiently long for the occurred in the mid-1920s and the area subsequently was polluting potential of the leachate to be greatly dimi- built over. Serious problems due to contamination of the nished. Indeed one of the methods of tackling the ground meant that in the late 1970s over 700 families had problem of pollution associated with landfills is by to be relocated (Elliott 1980). The cost of clearing up the dilution and dispersal of the leachate. Otherwise, leachate fill and relocating the residents was around $100 million. can be collected by internal drains within the landfill and One method of dealing with hazardous wastes is by conveyed away for treatment. containment. An additional requirement recommended Selection of a landfill site for a particular waste or a by Gray et al. (1974) to that used for domestic waste is mixture of wastes involves a consideration of economic that a site handling toxic wastes should be underlain by at and social factors as well as the hydrogeological condi- least 15 m of impermeable strata. Any well abstracting tions. As far as the latter are concerned, then, most groundwater for domestic use and confined by such argillaceous sedimentary, massive igneous and metamor- impermeable strata should be more than 2 km away. phic rock formations have low intrinsic permeability and Various barrier systems such as clay and/or geomem- therefore afford the most protection to water supply. By brane liners, slurry trench cutoffs, geomembrane cutoffs contrast, the least protection is provided by rocks, and internal drainage systems have been employed. The intersected by open fissures or in which solution features latter allow leachate to be conveyed away for treatment. are developed. Granular materials may act as filters. The A recent review of methods of containing hazardous position of the water table is important as it determines waste has been given by Mitchell (1986). whether wet or dry tipping is involved, as is the'thickness Disposal of hazardous waste has also been undertaken of unsaturated material underlying a potential site. by injection into deep wells located in rock below and Unless waste is inert, wet tipping should be avoided. The therefore isolated from fresh water aquifers, thereby hydraulic gradient determines the direction and velocity ensuring that contamination or pollution of underground of the flow of leachates when they reach the water table water supplies does not occur. In such instances the waste and also is related to both the dilution which the leachates generally is injected into a permeable bed of rock several undergo and to the points at which flow is discharged. hundreds or even thousands of metres below the surface Downloaded from http://egsp.lyellcollection.org/ by guest on September 27, 2021

22 F. G. BELL, J. C. CRIPPS, M. G. CULSHAW 8L M. O'HARA which is confined by relatively impervious formations. gical conditions are accurately evaluated and mapped However, even where geological conditions are favour- before the disposal programme is started. A system of able for deep-weU disposal the space for waste disposal observation wells sunk into the subsurface reservoir frequently is restricted and the potential injection zones concerned in the vicinity of the disposal well allows the usually are occupied by connate water. Accordingly any movement of waste to be monitored. In addition, shallow potential formation into which waste can be injected must wells sunk into fresh water aquifers permits monitoring of possess sufficient porosity, permeability, volume and water quality so that any upward migration of the waste confinement to guarantee safe injection. A further point can be readily noted. to consider is that induced seismic activity has been Radioactive waste may be of low or high level. Low associated with the disposal of fluids in deep wells level waste contains small amounts of radioactivity and so (Hollister & Weimer 1968). does not present a significant environmental hazard if Two important geological factors relating to the cost of properly dealt with. The dilute and disperse method construction of a well are its depth and the ease with frequently has been used to dispose of this material. which it can be drilled. As far as operating costs are Although many would not agree, it would appear that concerned these are governed by the permeability, poro- low-level radioactive waste can be disposed of safely by sity, and thickness of, and piezometric pressure in the burying in carefully controlled and monitored sites where injection zone since these determine the rate at which the the hydrological and geological conditions severely limit reservoir can accept the liquid waste. the migration of radioactivite material. Monitoring is especially important in deep-well dis- High level radioactive materials need to be separated posal that involves toxic or hazardous materials. Effective from biological systems for hundreds or even thousands monitoring requires that the geological and hydrogeolo- of years before they no longer represent hazards to health.

TABLE 5. Summary of the technicalfeasibility of alternat&e nuclear waste management systems (after Ang&o 1977).

General characteristics relative to feasibility

Storage method Favourable Unfavourable

Storage in geological formations Solid waste emplaced in mined cavity; no Ion exchange as backup fluid cooling or melting Solid waste emplaced in mined cavity; Ion exchange of rocks as backup Irreversible high temperature in rock initial water cooling; melting~ Solid waste emplaced in man-made struc- Ion exchange of rocks as backup; provides Requires interim operation by man ture in mined cavity; initial air cooling; no ready interim retrievability melting Solid waste emplaced in man-made struc- Ion exchange of rocks as backup; provides Requires interim operation by man ture in mined cavity; initial water cooling; ready interim retrievability no melting Solid waste emplaced in a matrix of drill- Ion exchange of rocks as backup Very poor retrievability and monitora- holes; no fluid cooling or melting bility; many penetrations to surface Solid waste emplaced in deep holes; no Ion exchange of rocks as backup; large Very poor retrievability and monitora- fluid cooling; melting or nonmeltingb distance from man's environment bility; deep geology unknowns Storage in ice sheets Self-melt through icer Great distance from man Extended transport; poor retrievability Anchored storage or disposal c Low temperature for cooling Extended transport Ice surface storage or disposal c Possible international solution Many technical unknowns Antarctica (subsurface burial in ice-free Great distance from man; low temperature Retrievability and monitorability good areas) for cooling; possible international solution Storage in the seabed Subduction zones and other deep-sea tren- Great distance from man; water for dilu- Extended sea transport; mobility of chesb,c tion seawater Stable deep-sea areas Ion exchange of sediments as backup Concentration by ecology Rapid sedimentation areas e Possible international solution Very poor retrievability and monitorability

Note: Favourable characteristics include: fair distance from the human environment; safety from storms and most human activities. Unfavourable characteristics include: some potential for penetration by humans in future; poor retrievability and monitoring; possible groundwater transport. Differences from these general points are indicated to the right of each method under the appropriate column. "This method can also involve in-place melting and conversion to a rock-waste matrix. bCannot be implemented with today's technology. CThese have an uncertain potential for providing adequate safety. Downloaded from http://egsp.lyellcollection.org/ by guest on September 27, 2021

ASPECTS OF GEOLOGY IN PLANNING 23

Their disposal therefore presents one of the most acute carbons are generally transmitted through porous media, problems of the present day. The disposal of high level although some fraction may be retained in the material. liquid waste can be achieved by solidifying and mixing it Usually, however, the most dangerous forms of ground- with inert material. It is then placed in steel and concrete water pollution are those which are miscible with the containers which may be stored in underground caverns water in the aquifer. or dumped into the oceans. Some long-term strategies Concentrated sources of pollution are most undesir- which have been suggested for the disposal of high level able because the self-cleansing ability of the soil in that radioactive waste are outlined in Table 5. Permanent area is likely to be exceeded. As a result the 'raw' pollutant storage in thick impermeable rock formations such as may be able to enter an aquifer and travel some salt, shale, granite or basalt more than 500 m below the considerable distance from the source before being surface is usually regarded as the most feasible means of reduced to a negligible concentration. A much greater disposal. The location should be in geologically stable hazard exists when the pollutant is introduced into an areas with a minimum risk of seismic disturbance. Deep aquifer beneath the soil horizon since the powerful structural basins are considered as possible locations for purifying processes that take place within the soil are disposal. bypassed and attenuation of the pollutant is reduced. This is most critical when the pollutant is added directly to the zone of saturation, because in most soils and rocks the Groundwater pollution horizontal component of permeability is usually much Walker (1969) defined pollution as 'an impairment of greater than the vertical one. Consequently, a pollutant water quality by chemicals, heat or bacteria to a degree then can travel a much greater distance before significant that does not necessarily create an actual public health attenuation occurs. This type of hazard often arises from hazard, but that does adversely affect such waters for poorly maintained domestic septic tanks and soakaways, normal, domestic, farm, municipal or industrial use'. He from the discharge of quarry wastes, farm effluents and used the term 'contamination' to denote impairment of sewage into surface water courses and from the disposal water quality by chemical or bacterial pollution to a of refuse and commercial wastes. degree that creates an actual hazard to public health'. It is generally assumed that bacteria move at a The greatest danger of groundwater pollution is from maximum rate of about two-thirds of the water velocity. surface sources including animal manure, sewage sludge, Since most groundwaters only move at a rate of a few leaking sewers, polluted streams, refuse disposal sites. metres per year, the distances travelled by bacteria are Area with a thin cover of superficial deposits or where an usually quite small and, in general, it is unusual for aquifer is exposed, such as a recharge area, are the most bacteria to spread more than 33 m from the source of the critical from the point of view of pollution potential. Any pollution. However, Brown et al. (1972) suggested that possible source of contamination in these areas should be viruses are capable of spreading over distances which carefully evaluated, both before and after any ground- exceed 250 m, although 20 to 30 m may be a more typical water supply well is constructed and the viability of figure. Of course, in porous gravel, cavernous limestone groundwater protection measures considered. One or fissured rock, bacteria and viruses may spread over approach to groundwater quality management is to distances of many kilometres. indicate areas with a high pollution potential on a map Induced infiltration occurs where a stream is hydrauli- and to pay particular attention to activities within these cally connected to an aquifer and lies within the area of vulnerable areas. influence of a well. When the well is over pumped, a cone The attenuation of a pollutant as it enters and moves of depression develops and spreads. Eventually the through the ground occurs as a result of biological, aquifer may be recharged by the influent seepage of chemical and physical processes. Hence the self-cleansing surface water, so that some proportion of the pumpage capacity of a soil-aquifer system depends upon the from the well is now obtained from the surface source. physical and chemical form of the pollutant, the nature of Induced infiltration is significant from the point of view of the soil/rock comprising the aquifer and the way in which groundwater pollution in two respects. Firstly, hydraulic the pollutant enters the ground. In general, the concentra- gradients may result in pollutants travelling in the tion of a pollutant decreases as the distance it has opposite direction to that normally expected. Secondly, travelled through the ground increases. Thus the greatest surface water resources are often less pure than the pollution potential exists for wells tapping shallow underlying groundwater so the danger of contamination aquifers that intersect or lie near ground level. is introduced. However, induced infiltration does not The form of the pollutant is clearly an important factor automatically cause pollution, and it is a common with regard to its susceptibility to the various purifying method of augmenting groundwater supplies in Europe. processes. For instance, pollutants which are soluble, North America and elsewhere. such as fertilizers and some industrial wastes, cannot be A list of potential groundwater pollutants would be removed by filtration. Metal solutions may not be almost endless, although one of the most common susceptible to biological action. Solids, on the other hand, sources is sewage sludge. This material arises from the are amenable to filtration provided that the transmission separation and concentration of most of the waste media are not coarse grained, fractured or cavernous. materials found in sewage. Since the sludge contains Karst or cavernous limestone areas pose particular nitrogen and phosphorus it has a value as a fertilizer. problems in this respect. Insoluble liquids such as hydro- While this does not necessarily lead to groundwater Downloaded from http://egsp.lyellcollection.org/ by guest on September 27, 2021

24 F. G. BELL, J. C. CRIPPS, M. G. CULSHAW ~ M. O'HARA pollution, the presence in the sludge of contaminants such that contamination, once established, may take many as metals, nitrates, persistent organic compounds and years to remove under natural conditions. Reduction of pathogens, does mean that the practice must be carefully pumping to eliminate overdraft or artificial recharging controlled. The widespread use of chemical and organic have been used as methods of controlling saline intrusion. pesticides or herbicides is another possible source of The routine monitoring of groundwater level and water groundwater contamination. quality provides an early warning of pollution incidents Run-off from roads can contain chemicals from many (Everett 1981). The first important step in designing an sources, and therefore represents another potential efficient groundwater monitoring system is the proper source of pollution, as do cemeteries. There are at least understanding of the mechanics and dynamics of con- two ways in which nitrate pollution of water is known or taminant propogation, the nature of the controlling flow suspected to be a threat to health. Firstly, the build-up of mechanism and the aquifer characteristics. There should stable nitrate compounds in the bloodstream reduces its be a sufficient number of wells to allow the extent, oxygen-carrying capacity. Infants under one year old are configuration and concentration of a contamination most at risk. A limit of 50 mg 1-1 of nitrate (NO3) has been plume to be determined. Furthermore, construction of a recommended by the World Health Organisation (WHO) water quality monitoring well must be related to the for European countries. Secondly, the possible combina- geology of the site, in particular, the well structure should tion of nitrates and amines through the action of bacteria not react with the groundwater if water quality is being in the digestive tract results in the formation of potentially monitored. These wells are frequently constructed using carcinogenic nitrosamines. inert plastic casings and screens. Monitoring also can be Nitrate pollution is basically the result of intensive carried out by using geophysical methods, especially cultivation due to the large quantity of synthetic nitroge- resistivity surveys. nous fertilizer used, although over-manuring with natural organic fertilizer can have the same result. Rapid trans- Surface subsidence formation into nitrate results in an ion which since it is neither adsorbed nor precipitated in the soil becomes Surface subsidence occurs as a consequence of the easily leached by heavy rainfall and infiltrating water extraction of mineral deposits or the abstraction of water, (Foster & Crease 1974). However, the nitrate does not oil or natural gas from the ground. The subsidence effects have an immediate affect on groundwater quality, poss- of mineral extraction depend on the type of deposit, the ibly because most of the leachate that percolates through geological conditions, in particular the nature and struc- the unsaturated zone as intergranular seepage has a ture of the overlying rocks or soils, the mining methods typical velocity of about 1 m per year. Thus, there may be and any mitigative action. In addition to subsidence due a considerable delay between the application of the to the removal of support, mining often entails the fertilizer and the subsequent increase in the concentration lowering of groundwater levels which, since the vertical of nitrate in the groundwater. This time lag, which is effective stress is raised, causes consolidation of the frequently of the order of 10 years or more, makes it very overburden. For instance dewatering associated with difficult to correlate fertilizer application with increased mining in the gold-bearing reefs of the Far West Rand, concentration of nitrate in groundwater. Hence, although South Africa, which underlie dolostone and unconsoli- nitrate levels are unacceptably high now, they may dated deposits produced differential subsidence over worsen in the future because of the increasing use of large areas and led to the formation of sinkholes (Fig. 15). nitrogenous fertilizer. Hence certain areas became unsafe for occupation and Measures that can be taken to alleviate nitrate pollu- were evauated. tion include better land-use management, mixing of water Many ore deposits are concentrated into veins or ovoid from various sources, or the treatment of high nitrate bodies, the mining of which may cause localized subsi- water before it is put into supply. In general, the ion dence. Transmission of a ground loss to the surface entails exchange process has been recommended as the preferred spreading its effect beyond the edges of mined area and means of treating groundwaters, although this may not be indeed can fracture the surface (Fig. 16). Hence the considered cost-effective for all sources. removal of a deep ore body is liable to cause subsidence Excessive lowering of the water table along a coast as a over a wider area than one of equal thickness at shallow consequence of over abstraction can lead to saline depth although, in the former case, the lowering of the intrusion, the salt water entering the aquifer via submar- ground surface will be less severe. On the other hand, the ine outcrops thereby displacing fresh water. However, the mining of stratiform deposits, especially the total extrac- fresh water still overlies the saline water and continues to tion of seams of coal can create subsidence problems over flow from the aquifer to the sea. The encroachment of salt wide areas. water may extend several kilometres inland. Typically The mining method is a very important consideration, chloride levels may increase from a normal value of not least because of the control it exerts over the amount around 25 mg 1- ~ to something approaching of mineral actually extracted during mining operations. 19 000 mg 1-1 compared with a recommended limit for The mining of coal prior to the 16th century usually took drinking water in Europe of 200 mg 1-1. Once intrusion the form of outcrop workings or bell-pitting. The latter develops it is not easy to control. The slow rates of are shaft-like excavations up to about 12 m deep which groundwater flow, the density differences between fresh extend down into the mineral seam. Once in the seam the and salt waters and the flushing required, usually mean workings extend outwards for a short distance. The Downloaded from http://egsp.lyellcollection.org/ by guest on September 27, 2021

ASPECTS OF GEOLOGY IN PLANNING 25

FIG. 15. Collapse of crushing plant into a sinkhole, Westdriefontein Mine, 1962. (Courtesy of Gold Fields of South Africa Ltd.).

extent of lateral workings depends on the stability of the excavation. Bell-pitting leaves an area of highly disturbed ground which generally requires treatment or complete excavation before it is suitable for use for any other purpose. Later coal workings were usually undertaken by the pillar and stall method. This method entails leaving pillars of the mineral in place to support the roof of the workings. The method also is used at the present day to work stratiform deposits including limestone, gypsum, anhydrite and sedimentary iron ores. The amount of mineral actually mined depends primarily on maintaining the stability of the excavation so that in weaker rock masses large pillars and small stalls will be formed. However, in many cases in old coal workings pillars were robbed prior to abandonment of the mine which increases the possibility of pillar collapse. Slow deterioration and failure of pillars may take place years after mining operations have ceased, although observations in coal mines at shallow depth together with the resistance of coal to weathering, suggest that this is a relatively uncommon feature at depths less than about 30 m. On the other hand, small pillars may be crushed out once the overburden exceeds 50 to 60 m. Old pillars at shallow depth have occasionally failed near faults and they may fail if they are subjected to the effects of subsequent longwall mining of coal. The yielding of a large number of pillars can bring about a shallow broad subsidence over a large area. This type of subsidence usually is very slow and so difficult to FIG. 16. The formation of a large tension fracture at the surface detect. due to the collapse of a pillar in limestone workings over 100 m Squeezes or crushes sometimes occur in a mine as a beneath, Middleton-by-Wirksworth, Derbyshire. result of the pillars being punched into either the roof or Downloaded from http://egsp.lyellcollection.org/ by guest on September 27, 2021

26 F. G. BELL, J. C. CRIPPS, M. G. CULSHAW ~ M. O'HARA floor bed, which might have become weakened or altered dence will be up to about 0.9 times the thickness of the by the action of water or weathering. Once again surface seam. Normally, however, the amount of surface subsi- subsidence adopts a trough-like or basin form and minor dence is significantly less than this amount. strain and tilt problems occur around the periphery of the Investigations carried out by British Coal have revealed basin thereby produced. Briggs (1929) reported that when that structural damage is not simply a function of ground pillars are forced into a yielding pavement subsidence strain but that the shape, size and form of construction may restart. This could take place many years after are also important controls (Geddes 1984). In many mining had ceased and could damage property. He instances subsidence effects also have been affected by the quoted an example in Wallsend where the surface subsi- geological structure, notably the presence of faults, and dence amounted to 1.2 m. the character of the rocks and soils above the workings Even if pillars in old shallow workings are relatively (Whittacker & Breeds 1977). A review of measures which stable the surface can be affected by void migration. Void can be taken to mitigate the effects of subsidence due to migration develops if roof rock falls into the worked-out coal working are provided by Anon (1975) and Anon zones and represents the main problem in areas of shallow (1977a). Methods of dealing with old shafts are outlined abandoned mines. It can occur within a few months, or a by Anon (1982). very long period of years after mining has ceased. The Deposits that readily go into solution, in particular salt, material involved in the fall bulks, so that migration is can be extracted by solution mining. Salt has been eventually arrested, although the bulked material never obtained by brine pumping in a number of areas in the completely fills the voids. Nevertheless the process can, at UK; Cheshire being by far the most important. Subsi- shallow depth, continue upwards to the surface leading to dence due to salt extraction by wild brine pumping still the sudden appearance of a crown-hole (Fig. 17). continues to be an inhibiting factor, for example, around The mining of coal by longwall methods is a more Droitwich, as far as major developments are concerned. recent innovation which has developed as a mechanized This is chiefly because of its unpredictable nature. mining system during the 20th century. It involves total The most successful wild brine pumping in Cheshire extraction of a seam. The working face is temporarily was carried out on the major natural brine runs. Active supported, the support being moved as the face advances, subsidence was normally concentrated at the head and leaving the roof from which support has been withdrawn sides of a brine run where fresh water first enters the to collapse. The resulting subsidence is largely contem- system (Bell 1975). Hence serious subsidence occurred at poraneous with mining, producing more or less direct considerable distances, up to 8 km from pumping centres. effects on any surface development (Brauner 1973). In addition, tension cracks and small fault scars formed in The surface effects of mining include not only lowering the surface tills on the convex flanks of subsidence but also tilting and both compressive and tensile ground hollows (Fig. 19). Because the exact area from which salt strains (Figs 18a and b). As longwall mining proceeds the is extracted was not known, the magnitude of subsidence ground is subject to tilting accompanied by tension and developed could not be related to the volume of salt then compression. Once the subsidence front has passed worked. Consequently there could be no accurate means by, the ground attains its previous slope and the ground of predicting the amount of ground movement or strain. strain returns to zero. However, permanent ground Hence any attempt to predict the amount and location of strains affect the ground above the edges of the extracted subsidence could only be done by the extrapolation of panel. For total mineral extraction and a low depth to past trends, a method which could not guarantee success. width extraction ratio, the maximum amount of subsi- In addition to the subsidence caused by the shrinkage

FIG. 17. This crown-hole suddenly appeared in a garden in Gateshead, it being due to void migration from abandoned shallow workings. (Courtesy of R. K. Taylor). Downloaded from http://egsp.lyellcollection.org/ by guest on September 27, 2021

ASPECTS OF GEOLOGY IN PLANNING 27

FIG. 20. The Holme Fen post is a cast iron pillar which was erected in 1851 on the south west edge of Whittlesey Mire. It replaced the wooden posts which had been erected in 1848 to indicate the shrinkage of peat due to drainage. The post was driven 22 feet (7 m) through the peat into the clay beneath until its top was flush with the ground. Within 10 years the ground level had fallen ! .5 m through shrinkage. Since then it has fallen a further 4 m.

FIG. 18. (a) Wave-like effect of subsidence due to longwall mining, which not only gives rise to a lowering of the surface but produces tilt and zones of compression and tension. (b) Subsi- dence damage produced by longwall mining necessitating the shoring up of houses and their evacuation prior to repair, Elsecarr, near Barnsley, Yorkshire.

FIG. 19. Subsidence trough caused by wild brine pumping of salt in Cheshire. Note the tension scars on the cambered flanks. The trough is now occupied, in part, by a flash and the road on which FIG. 21. Subsidence of the land surface in the Houston district of the car is standing had to be made up periodically. Texas, 1943-1964. (After Gabrysch 1969). Downloaded from http://egsp.lyellcollection.org/ by guest on September 27, 2021

28 F. G. BELL, J. C. CRIPPS, M. G. CULSHAW ~ M. O'HARA of peat following surface drainage, (Fig. 20), surface the Wilmington oilfield near Long Beach, California. By subsidence also occurs in areas where there is intensive 1966, after 30 years of production and eight of repressur- abstraction of fluids from the ground, especially oil or izing by injection, an elliptical area of more than 75 km 2 groundwater (Fig. 21), as well as natural gas. Subsidence had subsided more than 8.8 m. is attributed to the consolidation of the fluid bearing formations which results from the increase in vertical Induced seismicity effective stress. In most cases, and particularly in clayey deposits, the subsidence does not occur simultaneously Seismicity may be induced to occur as a result of the with the abstraction of fluid. activities of man. Most instances of this type have been The amount of subsidence which occurs is governed by associated with hydrocarbon extraction, underground the increase in effective pressure, the thickness and mining, large explosions, large reservoirs (Fig. 23) or compressibility of the deposits involved, the length of underground liquid waste disposal. Such activities time over which the increased loading is applied, and through the single or combined effect of loading or possibly the rate and type of stress applied. The ratio increased pore pressures in the rock masses concerned between maximum subsidence and reservoir consolida- allow the release of stored strain energy. The earthquakes tion can be estimated from the ratio between depth of produced tend to have magnitudes of less than 5, burial and the lateral extent of the reservoir (Geertsma although more serious events have occurred. For 1973). For instance, small reservoirs which are deeply instance, a 6.5 magnitude earthquake associated with the buried do not give rise to noticeable subsidence, even if Koyna Dam in India (Table 6) resulted in loss of life and subjected to considerable consolidation. By contrast, damage to the dam itself (Lane 1971). Evans (1966) extremely large reservoirs may develop significant subsi- documented induced seismicity in the Denver area which dence. was attributed to the disposal of liquid waste down a deep Besides the lowering of the ground surface, faults may well. Over 700 minor earthquakes of magnitudes up to 4.3 develop around the periphery of a subsiding basin (Fig. were recorded. 22). The faults themselves are high angled structures and Minor seismicity has also been caused by coal mining normal in type with the downthrown side on the side of (Kusznir et al. 1980) and nuclear explosions (Healy et al. the abstraction area. Although displacements may not be 1970). In the latter part of the 1970s minor earth tremors large, these features can be very damaging to structures, were recorded in the neighbourhood of Stoke-on-Trent particularly as they generally develop very suddenly. and were linked with mining at Hem Heath Colliery. The A reduction in the rate of abstraction can lead to a rise presence of old workings in the same area appeared to_be in groundwater levels. This, in turn, can lead to a rise in an additional causative factor. the ground surface; for example, in the Venice area there has been some 20 mm of rebound since 1970 (Carbognin et al. 1976). Although controlled withdrawal of ground- Data acquisition and presentation water permits the re-establishment of the natural hydraulic balance recovery uplift is never complete. Desk study and sources of data More than 40 known examples of differential subsidence, horizontal displacement or surface faulting have Usually a desk study is carried out after the planning stage been associated with 27 oil and gas fields in California and of a scheme has been largely completed. However, Texas. The most spectacular case of subsidence is that of Herbert et al. (1986) pointed out that significantly greater benefit can be derived if the desk study is carried out at an earlier stage. A desk study can aid the assessment of land potential, help determine the factors affecting the pro-

FIG. 22. Damage to a house caused by offset along the long Point Fault in Houston, Texas. The effect was caused by a decline in the groundwater level brought about by over-abstraction. (Courtesy FIG. 23. Distribution of earthquakes in time and in relation to of Thomas Holtzer, US Geological Survey). lake level at Kariba. (After Lane 1971). Downloaded from http://egsp.lyellcollection.org/ by guest on September 27, 2021

ASPECTS OF GEOLOGY IN PLANNING 29

TABLE 6. Some large reservoirs in relation to seismic activity (after Lane 1971).

Height Volume Capacity Seismicity Type of of dam of dam of reservoir after Dam Country dam (m) (m 3 x 103) (m 3 x 106) construction

Bhakra India Gravity 225 4130 9868 No record Contra Switzerland Arch 230 660 86 Slight Daniel Johnson Canada Multiple 214 2255 141975 No record (Manicopagan 5) arch Glen Canyon USA Arch 216 3747 33304 Nil Grancarevo Yugoslavia Arch 123 376 1277 Noticeable (M =4) Grande Switzerland Gravity 284 5957 400 Nil Dixence Grandval France Multiple arch 88 180 292 Noticeable Hoover USA Arch 221 3364 38296 Noticeable (M = 5) Kariba Rhodesia, Arch 128 1032 160368 Strong Zambia (M = 6) Koyna India Gravity 104 1300 2780 Strong (M=6.5) Kremasta Greece Earth 160 7800 4750 Strong (Roi Paul) (M=6.5) Kurobegawa Japan Arch 186 1360 199 No record No. 4 Mangla Pakistan Earth 115 65651 6358 Slight (M = 3.6) Mauvoisin Switzerland Arch 237 2030 180 Slight Monteynard France Arch 155 455 240 Noticeable (M=4.9) Oroville USA Earth 236 59639 4298 Slight (M = 1.5) Warragamba Australia Gravity 137 1233 2052 Noticeable

posed development and facilitate the planning of sub- known. In such cases a study of the relevant topographi- sequent ground investigations. At the planning stage of a cal and geological maps and memoirs, and possibly aerial project the desk study can range in scope from the photographs might provide sufficient information. On the preliminary rapid response to the fully comprehensive other hand, for large projects literature and map surveys search, depending upon the time and financial resources may save time and thereby reduce the cost of the available. However, the broad content of the study is exploration of the site. similar in each case. A desk study is based primarily on existing information Remote imagery and aerial photographs which can be obtained from a wide variety of sources. These sources can include topographic maps and plans; Remote sensing commonly represents one of the first aerial photographs and remote sensing imagery; geologi- stages of land assessment in underdeveloped areas. It cal maps and memoirs; land utilization maps; admiralty involves the identifcation and analysis of phenomena on charts; records of mineral workings; plans of existing the Earth's surface by using devices borne by air- or services; previous site investigation reports; soil maps and space-craft (Beaumont 1979). Most techniques used in hydrological and meteorological data. Other records and remote sensing depend upon recording energy from part information held by local authorities, libraries, various of the electromagnetic spectrum, ranging from gamma societies, universities and the general public at times may rays, through the visible spectrum to radar. The two be of value. However, some of this material may have to principal systems of remote sensing are infrared linescan be treated with caution. (IRLS) and side-looking airborne radar (SLAR). Signals A flow chart suggesting how a data search could be from several bands of the spectrum can be recorded carried out is given in Fig. 24. The effort expended in any simultaneously by multi-spectral scanners. Lasers are data search and literature review depends on the complex- also being developed for use in remote sensing. ity and size of the proposed project, as well as on the Imagery of the Earth's surface obtained by remote nature of the expected ground conditions. Detailed sensing gives a broad view of an area, illustrating searches for information can be extremely time consum- conditions as they exist at a particular time, and indicates ing and may not be justified for small schemes at sites the interrelationships between geology, landform, cli- where the ground conditions are relatively simple or well mate, vegetation and land-use. Small-scale imagery pro- Downloaded from http://egsp.lyellcollection.org/ by guest on September 27, 2021

30 F.G. BELL, J. C. CRIPPS, M. G. CULSHAW ~ M. O'HARA

Project Conception

Initial study of topographical maps, geological maps, memoirs, and aerial photographs

Are any particular geo- Consult specific technical hazards appar- sources of further ent or are there any significant information as gaps in the information YES relevant, e.g, mine ~. obtained? ~Jl records, old maps. pedological maps. etc.

Have any Consult site major developments been investigation reports planned or constructed close to and information on recently from which construction information may be J YES conditions if available

FIG. 24. Suggested flow chart for carrying out a data search and literature review for a site investigation. (After Chaplow 1975).

vides a means of initial reconnaissance which allows areas requiring more care in their production and controlled to be selected for further, more detailed investigation, photomosaics are based on a number of geodetically either by aerial and/or ground survey methods. In surveyed points. They can be regarded as having the same addition, small-scale imagery may enable regional geolo- accuracy as topographic maps. gical relationships and structures to be identified which The amount of useful information which can be are not noticeable on larger-scale imagery or mosaics. obtained from aerial photographs varies with the nature Obviously the value of such imagery is important where of the terrain and the type and quality of the photographs. existing map coverage is inadequate. For example, it can Generally they are of most use at the feasibility stage of be of use for the preparation of terrain classification development, that is, during the site selection and investi- maps, for regional engineering soil maps, for maps used gation planning stage. In other words they offer an for route selection, for regional inventories of construc- inexpensive means of providing information for a preli- tion materials, and for inventories of drainage networks minary appraisal of a large area. However, airphotos may and catchment areas. reveal features which cannot be detected easily from the Aerial photographs are generally taken at an altitude of ground. Aerial photographs can be taken rapidly for any between 800 and 9000 m, the height being governed by the locality and have proved particularly important where the amount of detail that is required. Photographs may be ground terrain is difficult and therefore impedes access. taken at different angles, however, vertical photographs For many purposes a scale of 1 : 10 000 is suitable. Colour are the most relevant for photogeological purposes. photographs may prove useful where the ground is Normally vertical aerial photographs have 60% overlap covered with vegetation. In this context infra-red colour is on consecutive prints on the same run, and adjacent runs more useful and also can be used for delineating water have a 20% overlap or side-lap. masses. Aerial photographs may be combined in order to cover Stereoscopic examination of aerial photographs allows larger regions. The simplest type of combination is the the terrain relief to be observed and, if required, contour uncontrolled print laydown which consists of photo- maps can be drawn, although the relief presented is graphs, laid along side each other, which have not been exaggerated so that slopes appear steeper than they really accurately fitted into a surveyed grid. Photomosaics are. As indicated below elementary geological maps can represent a more elaborate type of print laydown, be produced from aerial photographs. Indeed Norman & Downloaded from http://egsp.lyellcollection.org/ by guest on September 27, 2021

ASPECTS OF GEOLOGY IN PLANNING 31

Huntington (1974) summarized the uses to which aerial and undisturbed (Hvorslev ! 949). Disturbed samples can photographs can be put in the preliminary stages of an be obtained by hand, by auger or from the clay-cutter or investigation as follows: shell of a boring rig. An undisturbed sample ideally can be regarded as one which is removed from its natural (i) mapping and analysis of folding; condition without disturbing its structure, density, poro- (ii) mapping of regional fault systems and recording sity, moisture content and stress condition. Although no any evidence of relatively recent fault move- sample is ever totally undisturbed, every attempt must be ments and shear surfaces; made to preserve the original condition of these samples. (iii) determination of the number and geometry of Unfortunately mechanical disturbances produced when a joint systems; sampler is driven into the ground tend to distort the soil (iv) a study of the lithology and resistance to erosion structure. Furthermore a change of stress condition of surface rocks in relation to relief and land- occurs when a borehole is excavated. Undisturbed sam- forms; ples may be obtained by hand from surface exposures, (v) recording the distribution of superficial depo- pits and trenches. These samples are particularly useful sits; when it is necessary to test specific horizons, such as shear (vi) drainage studies which could take into account zones. surface run-off characteristics, boundaries of A number of different types of sampling tubes have catchment areas and stream divides etc, areas been developed for sampling soils. The standard sampling liable to periodic flooding, areas of subsurface tube for obtaining samples from cohesive soils is referred drainage (especially of cavernous limestone as to as the U100, it having a diameter of 100 mm and a illustrated by surface solution features), and length of approximately 450 mm. In soft materials two or relative permeability of the principal rock and three tubes may be screwed together to reduce distur- soil types at the surface; bance in the sample. A thin-walled piston sampler should (vii) an assessment of the stability of slopes (aerial be used to obtain samples of clays with a shear strength photographs are particularly useful in detecting lower than about 50 kN m -2 since these materials tend to certain failures which are difficult to appreciate expand into the sample tube. Where continuous samples during ground surveys); are required, particularly from rapidly varying or sensi- (viii) as an aid in the detection of old mine workings. tive soils, a Delft sampler or Swedish foil sampler may be used. The Bishop sand sampler occasionally has been Ground exploration used to obtain samples from saturated sand, one of the most difficult soils to sample. The aim of ground exploration is to try to determine, and Rotary percussion drills are designed for rapid drilling thereby understand, the nature of the ground conditions in rock. The rock is subjected to rapid high speed impacts of a particular area of interest and those of its surround- whilst the bit rotates, the rock being broken into fine ings (Clayton et al. 1982; Hawkins 1986). The extent to chippings. These can be identified as they are brought to which this stage of an investigation is carried out depends, the surface by the flushing medium. The technique is most to some extent, upon the size and importance of the effective in brittle materials. project. In fact, enough data for small projects can often Rotary drills are either skid-mounted, trailer mounted be collected by a preliminary reconnaissance. A ground or, in the case of the larger types, mounted on lorries. exploration programme must be concluded by a report They also are used for drilling through rock but, more embodying the findings and should contain geological importantly, can obtain core samples. plans of the area with accompanying sections, thereby The core is cut by a bit and housed in a core barrel. Core conveying a three-dimensional picture of the subsurface bits vary in diameter and accordingly core sticks of rock or soil formations. different diameters can be obtained. A variety of core Data relating to the subsurface conditions in soils can barrels is available for rock sampling. The single tube core be obtained by using hand or power augers, by wash barrel is the simplest type and as it is suitable only for hard boring (this tends not to be used in the United Kingdom) massive rocks, it is rarely used. The double tube swivel or by using a light cable and tool boring rig. The latter is core barrel is suitable for use in medium and hard rocks the most frequently used technique for investigating soils and triple tube barrels have been developed for obtaining in the United Kingdom. Rotary attachments are now cores from very soft rocks and from highly jointed and available which can be used with these rigs. However, cleaved rock. they are much less powerful than normal rotary rigs and There are no given rules regarding the location of tend to be used only for short runs as, for example, to boreholes or the depth to which they should be sunk. This establish the depth of rock head at the base of a borehole. depends upon two principal factors, namely, the geologi- Pits and trenches allow the ground conditions in soils and cal conditions and the type of project concerned. The highly weathered rocks to be examined directly although information provided by a preliminary reconnaissance or they are limited as far as their depth is concerned. the desk study should help provide a basis for the initial Samples are taken so that a detailed examination of the planning and layout of the borehole programme. Bore- material can be made and so that it can be subjected to holes should be located so as to explore fully the various tests. As far as sampling in soils is concerned the geological sequence and structure, obviously the more samples may be divided into two main types, disturbed complex these are, the greater the number of holes Downloaded from http://egsp.lyellcollection.org/ by guest on September 27, 2021

32 F.G. BELL, J. C. CRIPPS, M. G. CULSHAW & M. O'HARA needed. In some instances it may be as well to start with a measure groundwater pressures. They are usually sealed widely spaced network of boreholes. As information is into separate zones in boreholes so that the pore water obtained further holes can be put down, if and where pressures of each may be measured. necessary. Exploration should be carried out to a depth The direction of water flow can be determined by which includes all rock and soil formations likely to be monitoring either dyes, saline injections or radioactive significantly affected by the proposed structure. tracers, which are introduced into the groundwater via The data obtained from a borehole should be docu- boreholes. In some instances it may be necessary to mented on a borehole log. The fundamental requirement sample groundwater in order to carry out a chemical of this is to show how the sequence of strata changes with analysis especially to assess its sulphate content or pH depth. Individual rock types are generally presented in value. symbolic form together with a complete description Geophysical methods are used to determine the geolo- including an assessment of the degree of weathering, gical sequence and structure of subsurface rocks by the fracture index and relative strength (Anon 1970, 1977b). measurement of certain physical properties or forces. Numerous types of in situ tests have been developed to They frequently can provide subsurface information over assess the performance of the ground if it is difficult or a large area at reasonable cost. The information obtained impossible to sample. One of the most commonly used in may help to eliminate less favourable alternative sites, aid situ tests is the penetrometer test in which a conical point the locating of test holes in critical areas and prevent attached to a drive rod is forced into the ground either by unnecessary repetitive drilling in fairly uniform ground, hammer blows or by jacking. Measurement of either the as well as detecting variations in subsurface conditions dynamic or static resistance to penetration gives an between boreholes. Nonetheless boreholes are usually indication of the strength and density of soils. necessary in order to aid interpretation and correlation of Because soft clays may suffer disturbance when sam- the geophysical measurements. pled and thereby give unreliable results when tested for The properties which are made most use of in geophysi- strength in the laboratory, a vane test is often used to cal exploration are density, elasticity, electrical conducti- measure the in situ undrained shear strength. The plate vity, magnetic susceptibility and gravitational attraction. loading test provides valuable information by which the In other words seismic and resistivity methods record the bearing capacity, settlement and deformation character- artificial fields of force applied to the area under investiga- istics of the ground can be assessed, an incremental load tion whilst magnetic and gravitational methods measure being applied by a jack. Loads of up to two or three times natural fields of force. The former techniques have the the proposed loading are generally applied although, in advantage over the latter in that the depth to which the clays the load is increased until the settlement equals 10 to forces are applied can be controlled. By contrast, the 20% of the plate dimension or the rate of increase of natural fields of force are fixed and can only be observed, settlement becomes excessive. not controlled. Seismic and resistivity methods are more The Menard pressuremeter consists essentially of a applicable to the determination of horizontal or near probe which is placed in a borehole, at the end of the drill horizontal changes or contacts, whereas magnetic and rods, at a given depth, and then expanded. Hence the test gravimetric methods are generally used to delineate provides an assessment of the strength of soils or lateral changes or vertical structures. weathered rocks as well as their deformation modulus. Geophysical logging of boreholes can yield consider- The self-boring pressuremeter has a special cutting head able supplementary details and aid interpretation of so that it can be drilled into soft soils. It measures the surface geophysical surveys. The results can help with the lateral stress, undrained stress-strain properties and the identification of individual horizons and correlation peak strength of the soil. The dilatometer is a type of between boreholes, as well as providing information pressuremeter which is used to determine the deformabi- relating to rock properties. Logging can be done by lity of rock masses in drillholes. electrical, sonic or radioactive methods. The determination of field permeability and groundwater level, together with its fluctuations, are an essential part of a large site investigation. This may be accom- Terrain evaluation plished by performing either falling head or rising head permeability tests in boreholes. Wherever possible a rising Terrain evaluation is only concerned with the uppermost and a falling head test should be carried out at each part of the land surface of the Earth, that is, depths of less required level and the results averaged. Alternatively a than 6 m, excluding permanent masses of water. Mitchell constant head test may be used, water being added at a (1973) described terrain evaluation as involving the constant rate to maintain a steady state. analysis (the simplification of the complex phenomena The permeability of a bed of rock is determined by a which make up the natural environment), classification water injection or packer test carried out in a drillhole. (the organisation of data in order to distinguish and This is done by sealing off a length of uncased hole with characterize individual areas), and appraisal (the manipu- packers and injecting water under pressure into the test lation, interpretation and assessment of data for practical section. ends) of an area of the Earth's surface which is of interest Differences in the water carrying capacities of soils or to planners and engineers. There are two different rocks give rise to variable water pressures, at different approaches to this in terrain evaluation, namely, para- depths within the ground. Piezometers are used to metric evaluation and landscape classification. Para- Downloaded from http://egsp.lyellcollection.org/ by guest on September 27, 2021

ASPECTS OF GEOLOGY IN PLANNING 33 metric land evaluation refers to the classification of land Land regions are usually mapped at a scale between on a basis of selected attribute values appropriate to the 1 : 1 000 000 and 1 : 5 000 000. particular study; for example, class of slope or the extent Most land system maps are accompanied by a report of a certain kind of rock. The simplest form of parametric which gives the basic information used to establish the map is one which divides a single factor into classes. classification of landforms within the area surveyed. The Landscape classification is based on the principal geo- occurrence of land facets is normally shown on a block morphological features of the terrain. diagram, cross section or a map; maps are more often Terrain evaluation is a useful means of providing used in areas where the relative relief is very small such as information for preliminary surveys. It also offers a alluvial plains. The descriptions of land facets include rational means of correlating known and unknown areas, data on slope and soil profile, with vegetation and water that is, of applying information and experience gained regime referred to where appropriate. about one area to another one. This is based on the fact that the landscape systems of terrain evaluation have indicated that landscapes in different parts of the world Engineering geomorphological and geological maps are sufficiently alike to make feasible predictions from the known to the unknown. The purpose of an engineering geomorphological map is The following units of classification of land have been to portray the forms of the surface, the nature and recognized for purposes of terrain evaluation, in order of properties of the materials of which these surfaces are decreasing size, namely, land zone, land division, land composed and to indicate the type and magnitude of the province, land region, land system, land facet and land processes in operation (Figs 25a, b and c). As such they element. The land system, land facet and land element are provide a comprehensive, integrated statement of land the principal units used in terrain evaluation (Lawrence form and drainage. Consequently much information of 1978; Anon 1978). potential value for land-use planning and construction A land systems map shows the subdivision of a region projects are included. What is more, geomorphological into areas with common physical attributes which differ maps give a rapid appreciation of the nature of the from those of adjacent areas. Land systems are usually ground and thereby help the design of more detailed recognized from aerial photographs, the boundaries investigations, as well as focusing attention on problem between different land systems being drawn where there areas. Such maps recognize landforms along with their are distinctive differences between land form assem- delimitation in terms of size and shape. blages. Land systems maps are usually prepared at scales In the case of a construction project an understanding of 1 : 500 000 or 1 : 1 000 000. More detailed maps may be of the past and present development of an area is likely to required in complex terrain. These provide background aid prediction of its future behaviour. Hence geomorpho- information which can be used in a preliminary assess- logical maps should show how surface expression will ment of the ground conditions in the area under consider- influence an engineering project and should provide an ation and permit locations to be identified where detailed indication of the general environmental relationship of investigations may prove necessary. the site concerned. Recognition of the interrelationships A land system comprises a number of land facets. Each between land forms on site and those beyond the site is land facet possesses a simple form, generally being fundamental. This is because it is necessary to appreciate developed on a single rock type or superficial deposit. The not only how the site conditions will affect the engineering soils, if not the same throughout the facet, at least vary in but how the engineering will affect the site and the a consistent manner. An alluvial fan, a levee, a group of surrounding environment. sand dunes or a cliff are examples of a land facet. Indeed Doornkamp et al. (1979) suggested that if planners and geomorphology frequently provides the basis for the engineers are to obtain maximum advantage from a identification of land facets. Land facets occur in a given geomorphological survey, then derivative maps should be pattern within a land system. They may be mapped from compiled from the geomorphological data. Such deriva- aerial photographs at scales between 1:10000 and tive maps generally are concerned with some aspect of 1:60 000. ground conditions, such as landslips or areas prone to A land facet may, in turn, be composed of a small flooding or over which sand-dunes may migrate. number of land elements, some of which deviate some- The scale of a geomorphological map is influenced by what in a particular property, for example, in respect of the requirement of the project and therefore should focus soil type, from the general character. They represent the attention on the information relevant to that project. smallest unit of landscape that is normally significant. For Maps produced for extended areas, such as needed for example, a hill slope may consist of two land elements, an route selection, are drawn on a small scale. Small-scale upper steep slope and a gentle lower slope. Other maps also have been used for planning purposes, land-use examples of land elements include small river terraces, evaluation, land reclamation, flood plain management gully slopes and small outcrops of rock. and coastal conservation. These general geomorphologi- Although nearly all terrain evaluation mapping is cal maps concentrate on portraying the form, origin, age carried out at the land system level, the land region may and distribution of landforms, along with their formative be used in a large feasibility study. A land region consists processes, rock type and surface materials. In addition, if of land systems which possess the same basic geological information is available, details of the actual frequency composition and have an overall similarity of landforms. and magnitude of the processes can be shown by symbols, Downloaded from http://egsp.lyellcollection.org/ by guest on September 27, 2021

34 V. G. BELL, J. C. CRIPPS, M. G. CULSHAW ~ M. O'HARA

annotation, accompanying notes or successive maps of temporal change. Both topographical and geological maps (together with accompanying memoirs) contain much basic data which can be used in planning, particularly if a decision on the choice of sites has to be made. Nevertheless, from the point of view of the planner and engineer one of the shortcomings of conventional geological maps is that the boundaries are stratigraphical, that is, based on geological time intervals, and more than one type of rock may be included in a single mapped unit. What is more, conventional geological maps are lacking in quantitative information concerning the physical properties of the rocks and soils, the amount and degree of weathering and the hydrogeological conditions. However, the last two decades have seen much progress in the development of engineering geological maps. These may be simply geological maps to which engineering geological data have been added, or alternatively the rocks and soils in the area concerned may be presented as mapped units defined in terms of engineering properties or behaviour. The boundaries of these units may bear no relationship to the lithostratigraphical units or geological structure generally represented on conventional geological maps. This type of map is often referred to as a geotechnical map. The final map is produced from the information collected from various sources (literature survey, aerial photographs and imagery, and fieldwork). Large projects may require that a series of derivative maps are produced. The latter sometimes take the form of transparent overlays or a geotechnical 'atlas'. In the case of urban areas, the preparation of engineering geological maps frequently involves systematic searches of archives. Infor- Specification of geornorphological units mation from site investigation reports, records of past

1 2 3 4 5 6 7 8 9 and present mining activity, successive editions of Ord- nance Survey plans and other sources of information may 'c o~,o~e~ Morphogenetic characteristics ~ .~ c= ~ ~ e prove extremely useful. The information thereby obtained is plotted in plan and indexed on a documen- 011 0-1 Upper surface SCq I 1 N P MG tation map. 012 0-1 Upper surface SC I 1 N P MG 021 1~ Upper surface upper bounding slope SC h 2 LI I G Once the data have been gathered there are then the 022 1,1,,--4 Upper surface upper bounding slope SC T 2 S I G problems of how they should be represented on the map 042 0-1 Middle surface CSb It 1 LI W G 051 2-4 M~ldle surface upper bounding slope CSg T 2 S M MG and at which scale the map should be drawn. The latter is 062 4,1,-9 Middle surface middle bounding slope CSg Tw 3 S W M very much influenced by requirement, in other words the 082 1-3 Incised superficial channel CSg It 2 LI M M more detailed a map needs to be, the larger its scale. As far 091 ~ Basalsurface CSb I 1 N W G 092 ,1.,-4 Basal surface CSg T 2 S W M as presentation is concerned, this may involve not only 101 0-2 Welland grovel terraces $Gc I 1 N W G the choice of colours and symbols, but also the use of 102 0-2 Welland gravel terraces SGc It 2 LI W G overprinting (Anon 1972). 111 5-20 Meander bluff CSg W 5 L M M 112 5-20 Meander bluff SC W 3 L M M An engineering geological map provides an impression 122 1~ Meander slip-off slope SC T 2 LI M M of the geological environment, surveying the range and 160 0-189 Localised fault-bounded block $Csh I 1 N M MG 170 0-.} Welland flood -plain MC Iw 1 At P MG type of engineering geological conditions, their individual NOTES: Cleue= components and their interrelationships. A map, how- TOpSOil Creep Water movement Soil transport Drainage class ever, represents a simplified model of the facts and the C ChW 1 Slope-sine 0-0.1 I InfiltratiOn N No loss P Poor ! _S.nd 2 Slope-.ine 0,1-0.2 T Throug..... U L...... l tl.t complexity of various dynamic geological factors can M 5lit 3 Slope.sine 0.2-0.3 W Wash L Lou M Moderate G Gravel 4 Slope-nine0.3-0.4 Steady state W Well-drained never be portrayed in their entirety. The amount of b 8locks S Slope.line 0.4+ Ar Accumulltion with q chalk ertatics removll in flood Orlinage control simplification required is governed principally by the sh shale fragments M Morphology purpose and scale of the map, the relative importance of G Geology particular engineering geological factors or relationships, FIG. 25. (a) Map of morphology and slope angles (b) Map of the accuracy of the data and on the techniques of genesis (c) Map of geomorphological units. (After Knott et al. representation employed. Engineering geological maps 1980). should be accompanied by cross-sections (which can be Downloaded from http://egsp.lyellcollection.org/ by guest on September 27, 2021

ASPECTS OF GEOLOGY IN PLANNING 35

Commercial and industrial development, Open space includmg recreational larger resi- complexes dential build- including ski ings such as Low-value Residential Development areas, but hal condoma0aums lightweight Agriculture associated and apt agricultural uses grazing High densily Low density Roads Uti}ities structures buildings buildings and similar 3+ ABCDEFH 3 ABCDFH 3+ ABCDEFH 2 ABCEFIt I+ AB 3+ ABCFH 2+ AFH {+ ABE Remedial May be possible Typically not Compatible with Commonly Maintenance Maintenancecosts Usually minor engineering with careful feasible without open-space land feasible, costs probably may be high. problems except typicaffy is engineering, carefuJ use. Maintenance will be high. for irrigation prohibitively engineering, costs may be ditches and expensive, high. fences. Landsl~e-ea~h flow area 3 ACDEFH 2+ ACDEFH 3 ACDEFH I+ ACFH I AF 3 ACDEFH 2 AFH I ADE Remedial Remedial Remedial Remedial Commonly Remedial Remedial Usually minor engineering engineering engineering engineering feasible, engineering engineering problems except usually may be usually may be necessary, necessary, wbere ditch necessary, necessary, necessary, necessary, leakage causes earthflows. Unstable slope 3 CDEF 2 CDEF 2+ABCDEFH I CDE 0 F 2 ACFH 2 ACFH 0 E Remedial Remedial May experience Careful planning Typg:ally no Remedial Remedial Usually minor A engineering may engineering may difffculties can minimise difficulties, engineering engineering problems e~cept Z be necessary be necessary, without careful hazard, necessary, necessary in areas of A planning/ intense cuhi- engineering ,,a lion of R Potentially unstable hilisiopes. D slope S 3+ ABCF'H 3 ABCFH 3 ABCF'H 2 ABCH I+ B 2 ABCH 2+ ABCFH I B Rarely cam- Careful siting Remedial Careful planning Careful siting Maintenan~ Careful siting Usually few or M patible without typically engineering can can minimise can minimise costs probabb can minlmise minor problems, A elaborate and necessary to minimise hazard, hazard, will be high. hazard, expensive minimisr hazard. P mitigation, hazard. Rock fall area 3+ BCDFH 3 BCDFH 3 BDH 2 BFH 2 B 2 BCDFH 2 BDFH 0 B Rarely corn- RaYely corn- Compatible only Possibly Commonly Occasional very Occasional very Usually few or patible without patible without with elaborate excessive feasible if high main- high main- minor problems. elaborate and elaborate and and expensive maintenance rise is tenunce costs tenan~e costs expensive expensive mitigation, necessary, acceptable, can be expected, can be espected. mitigation, mitigation. Mudflow-debris fan area 3 GH 2+ GH 3 GH O G I G 2+ GH 2 GH 0 G Basements and Basements and Usually difficult Some remedial Usually little May require May I~luire Desirable for septic tank septic tank --depends on engineering may diffacuhy, special special many kinds of sewage disposal sewage disposal type of be neo~'ssary in Possibility of construction construction agriculture. usually not usually not development, unusual cases, flood damage, techniques techniques feasible, feasible, Flood plain remedial remedial High water delerminatton engineering engineering, table area may be necessary.

EXPLANATION OF CHART SYMBOLS MEANING OF LEI"rER SYMBOLS 3 High hazard A Especially severe on slopes greater than 30%. 2 Moderate hazard I Low hazard B Slope movement intermittent dependent on variation in weather 0 Very low, if any hazard or other factors. C Oversteepening or cutting of slopes can increase hazard greatly. D Artificial or natural increase in ground moisture can increase Typical potential hazard Conditions affecting actual hazard greatly. for" indicated ~. /deqree of hazard E Removal of natural vegetation can increase hazard greatly. land use F Hazard may decrease considerably as slope decreases. G Varies seasonably. Comments applicable H Detailed engineering geology studies necessary during pre* Example to most cases planning stages of development. FIG. 26. The matrix relates to Fig. 10 and is formatted so as to indicate to the map user that several geological and geology-related factors should be considered when contemplating the indicated land use in a given area. The matrix can also serve to recommend additional types of engineering geological studies that may be needed for a site. Thus the map can be used to model or anticipate the kinds of problems that a land-use planner or land developer may have to overcome before a particular activity is permitted or undertaken. (After Soule 1980). annotated) and an explanatory text and legend. In the required by planners and engineers is of a varied nature, case of hazard maps (for example, Fig. 10), they can be then the maps produced to meet these requirements are of accompanied by a land-use/geological hazard area matrix different types (Forster & Culshaw 1987). Hence maps are (Fig. 26) which provides some idea of the enginering generally compiled to meet a specific need. One of the problems which may arise in the area represented by the primary aims of engineering geological maps is to provide map. For instance, in the case of a landslide hazard map planners and engineers with information which will assist the matrix could indicate the effects of any changes in them in the planning of land-use and the location, slope or the mechanical properties of rocks or soils, and construction and maintenance of engineering structures could attempt to evaluate the severity of hazard for of all types. An appreciation of which aspects of the various land-uses. engineering geological environment might affect the Engineering geological maps and plans are used mainly successful completion of a project is of special impor- for planning purposes and because the information tance, as is the critical assessment of the influence that the Downloaded from http://egsp.lyellcollection.org/ by guest on September 27, 2021

36 F. G. BELL, J. C. CRIPPS, M. G. CULSHAW t~ M. O'HARA construction operations, and the finished structure, might attributes are frequently gradational. Obviously where have on the environment. A harmonious relationship one physical attribute grades imperceptibly into another between the two should be maintained as far as possible. it can be misleading to show a line on a map. This problem Hence an engineering geological map should portray the is particularly significant in the case of hazard maps (for information required to evaluate the engineering geologi- example, of landslipped or subsidence affected areas) cal aspects of the environment, especially in relation to since the hazard may carry with it a degree of blight which regional planning or civil or mining engineering. Ideally may then affect areas in which the hazard is insignificant. the map should convey its information without the user In such situations it is worth considering methods of having to read a large accompanying explantory text. showing gradational relationships by using techniques Secondly, it should facilitate the prediction of change in such as air-brushed colour shading, or by the use of the engineering geological environment likely to occur obviously artificial boundary lines, such as dashed line to due to the proposed undertaking. Thirdly, it should denote boundaries whose precise locations are uncertain. present information in a manner which can be readily understood by professional users. ACKNOWLEDGEMENTS: The efforts of Dinah Bridger in rapidly, Engineering geological maps usually are produced on and accurately, word processing the original manuscript are the scale of 1:10 000 or smaller whereas engineering gratefully acknowledged. geological plans, being produced for a particular engineering purpose, have a larger scale. The scale of the finished map may well differ from that at which the data are assembled and processed. In terms of engineering in References particular, the scale of the output must be such as to show ALGERMISSEN, S. T. & PERKINS, D. M. 1976. United States the smallest feature that could have a significant effect on Geological Survey Open File Report 76--416. the development for which the map is intended, together AMBRASEYS, N. N. 1974. Notes on engineering seismology. In: with the smallest construction that is planned. In this way SOLNES, J. (ed.) Engineering Seismology and Earthquake the interaction between construction and the geological Engineering. NATO Advanced Studies Institute Series, environment can be predicted. Applied Sciences, 3, 33-54. Engineering geological maps may serve a special ANGINO, E. E. 1977. High-level and long-lived radioactive waste purpose or be multi-purpose (Dearman & Matula 1972; disposal. Science, 198, 885-90. ANON. 1970. The logging of rock cores for engineering purposes. Anon 1976). Special-purpose maps provide information Engineering Group of the Geological Society Working Party on one specific aspect of engineering geology such as Report. Quarterly Journal of Engineering Geology, 3, 1-24. grade of weathering, jointing patterns or mass permeabi- ANON. 1972. The preparation of maps and plans in terms of lity. On the other hand, they may serve one particular engineering geology. Engineering Group of the Geological purpose as, for example, the engineering geological Society Working Party Report. Quarterly Journal of Engineer- conditions at a dam site or along a routeway, or for ing Geology, 5, 293-381. zoning for land-use in urban development. Multi-purpose ANON. 1975. Subsidence Engineers' Handbook, National Coal maps cover various aspects of engineering geology and Board, London. are often produced to meet national or regional require- ANON. 1976. Engineering Geological Maps. A Guide to their ments. Preparation. Unesco Press, Paris. ANON. 1977a. Ground Subsidence. Institution of Civil Engineers, In addition, engineering geological maps may be London. analytical or comprehensive. Analytical maps provide ANON. 1977b. The logging of rock cores for engineering details, or evaluate individual components, of the geolo- purposes. Second Report by the Engineering Group of the gical environment. Examples of such maps include those Geological Society Working Party. Quarterly Journal of showing degree of weathering or seismic hazard. Compre- Engineering Geology, 10, 43-52. hensive maps either depict all the principal components of ANON. 1978. Terrain evaluation for highway engineering and the engineering geological environment or are maps of transport planning. Transport and Road Research Laboratory, engineering geological zoning, delineating individual ter- Report SR448, Department of the Environment, Crowthorne. ANON. 1981. Basic geotechnical description of rock masses. ritorial units on a basis of uniformity of the most International Society of Rock Mechanics Commission on the significant attributes of their engineering geological Classification of Rocks and Rock Masses. International character. Journal of Rock Mechanics and Mining Sciences and Geome- Engineering geological (that is, geotechnical) maps and chanical Abstracts, 18, 85-110. plans indicate the distribution of units, defined in terms of ANON. 1982. The Treatment of Disused Mine Shafts and Adits. engineering properties. For instance, engineering geologi- National Coal Board, London. cal maps can be produced in terms of index properties, ATTEWELL, P. B. 8/; SANDFORD, M. R. 1974. Intrinsic shear rock quality or grade of weathering. The unit boundaries strength of a brittle, anisotopic rock. I- Experimental and are then drawn for changes in the particular property. mechanical interpretation. International Journal of Rock Mechanics and Mining Sciences, 11,423-30. Frequently the boundaries of such units coincide with BAKER, P. E. 1979. Geological aspects of volcano prediction. stratigraphical boundaries. In other instances, as for Journal of the Geological Society, London, 136, 341-6. example, where rocks are deeply weathered, they may BARBER, C. 1982. Domestic waste and leachate. Notes on Water bear no relation to geological boundaries. Unfortunately Research No. 31, Water Research Centre. Medmenham, one of the fundamental difficulties in preparing geotech- England. nical maps arises from the fact that changes in physical BEAUMONT, T. E. 1979. Remote sensing for location and Downloaded from http://egsp.lyellcollection.org/ by guest on September 27, 2021

ASPECTS OF GEOLOGY IN PLANNING 37

mapping of engineering construction materials. Quarterly Ground Movements and their Effects on Structures, Surrey Journal of Engineering Geology, 12, 147-58. University Press, London, 303-20. BELL, F. G. 1975. Salt and subsidence in Cheshire, England. ECK, W. & REDFIELD, R. C. 1965. Engineering geology problems Engineering Geology, 9, 237-46. at Sanford Dam, Texas. Bulletin of the Association of Engineer- 9 1981.Geotechnical properties of some evaporitic rocks. ing Geologists, 3, 15-25. Bulletin of the International Association of Engineering Geo- ELLIOTT, J. 1980. Lessons from Love Canal. Journal of the logy, 24, 137-44. American Medical Association, 240, 2033-4, 2040. --. 1983. Engineering Properties of Soils and Rocks, Second EVANS, D. M. 1966. Man-made earthquakes in Denver. Geo- Edition. Butterworths, London. times, 10, 11-18. BOOTH, B. 1979. Assessing volcanic risk. Journal of the Geological EVERETT, L. G. (ed.) 1981. Groundwater Quality Monitoring, Society, London, 136, 331-40. General Electric Co., Schenectady, New York. BRAUNER, G. 1973. Subsidence Due to Underground Mining. Part FORSTER, A. & CULSHAW, M. G. 1987. Engineering geological L Theory and Practice in Predicting Surface Deformation. maps as an aid to planning. In: Proceedings of the UNESCO United States Department of the Interior, Bureau of Mines, Subcommissionfor Maps on Environmental Geology Internatio- Washington. nal Symposium on Geological mapping in the service of BRIG6S, H. 1929. Mining Subsidence. Arnold, London 9 environmental planning, Trondheim, Norway, May 1986. In BROWN, R. H., KONOPLYANSTEV, A. A., INESON, J. & KOVA- press 9 LEVSKY, V. S. (eds) 1972. Groundwater Studies: An Internatio- FOSTER, S. S. D. & CREASE, R. I. 1974. Nitrate pollution of Chalk nal Guide for Research and Practice. Studies and Reports in groundwater in east Yorkshire--a hydrogeological ap- Hydrology, 7, UNESCO, Paris. praisal. Journal of the Institute of Water Engineers and BURNETT, A. D. & FOOKZS, P. G. 1974. A regional engineering Scientists, 28, 178-94. geological study of the London Clay in the London and FOURNIER D'ALBE, E. M. 1979. Objectives of volcanic monitor- Hampshire basins. Quarterly Journal of Engineering Geology, ing and prediction. Journal of the Geological Society, London, 7, 257-95. 136, 321-6. BURTON, I., KATES, R. W. & WHITE, G. F. 1978. The Environment GABRYSCH, R. K. 1969. Land surface subsidence in the Hous- as Hazard. Oxford University Press, New York. ton - Galveston region, Texas 9Proceedings of the Internatio- CARBOGNIN, L., GATTO, P., MozzI, G., GAMBOLATI, G. & nal Symposium on Land Subsidence, Tokyo. UNESCO Publi- RICCERI, G. 1976. New trend in the subsidence of Venice. cation 88, 1, 43-54. Proceedings of the Second International Symposium on Land GEDDES, J. D. 1984. Structural design and ground movement. In: Subsidence, Anaheim, International Association of Hydrologi- ATTEWELL, P. B. AND TAYLOR, R. K. (eds). Ground Movements cal Sciences, UNESCO Publication 121, 65-81. and their Effects on Structures, Surrey University Press, CHANDLER, R. J. 1969. The effect of weathering on the shear London, 243-67. strength properties of the Keuper Marl, Geotechnique, 19, GEERTSMA, J. 1973. A basic theory of subsidence due to reservoir 321-34. compaction; the homogeneous case. Nederland Geology, Mijn- C~PLOW, R. C. 1975. Engineering geology and site investiga- bouwk, 28, 43-62. tion. Part 1. Introduction. Ground Engineering, 8, 3, 34-8. GILLOTT, J. E. 1979. Fabric, composition and properties of CLAYTON, C. R. I., SIMONS, N. E. & MATHEWS, M. C. 1982. Site sensitive soils from Canada, Alaska and Norway. Engineering Investigation: A Handbook for Engineers, Granada, London. Geology, 14, 149-72. CLEVENGER, M. A. 1958. Experiences with loess as a foundation GRAY, O. A., MATHER, J. D. & HARRISON, I. B. 1974. Review of matrial. Transactions of the Ameriean Society of Civil Engi- groundwater pollution for waste sites in England and Wales neers, 123, 151-80. with provisional guidelines for future site selection, Quarterly COOKE, R. U. & DOORNKAMP, J. C. 1974. Geomorphology in Journal of Engineering Geology, 7, 181-96. Environmental Management. Clarendon Press, Oxford. GRIM, R. E. 1962. Applied Clay Mineralogy, McGraw-Hill, New --, GOUDIE, A. S. & DOORNKAMP, J. C. 1978. Middle East- York. review and bibliography of geomorphological contributions. HAWKINS, A. B. (ed.) 1986. Site Investigation Practice. Assessing Quarterly Journal of Engineering Geology, 11, 9-18. BS 5930. Engineering Geology Special Publication of the COTECCHIA, V. 1978. Systematic reconnaissance mapping and Geological Society, London, 2. registration of slope movements. Bulletin of the International HAYS, W. W. & SHEARER, C. E. 1981. Suggestions for improving Association of Engineering Geology, 17, 5-37. decision making to face geologic and hydrologic hazards. In: CRIPeS, J. C. & TAYLOR, R. K. 198 I. The engineering properties HAYS, W. W. ed.), Facing geologic and hydrologic hazards -- of mudrocks. Quarterly Journal of Engineering Geology, 14, earth science consideration. United States Geological Survey 325-46. Professional Paper 124OB, B 103-B 108. DAVENPORT, C. A. 1987. Earthquake engineering geological HEALY, J. H., HAMILTON, R. M. • RAYLEIGH, C. B. 1970. hazards in west and central Scotland. Engineering Group Earthquakes induced by fluid injection. Tectonophysics, 9, Meeting, Geological Society, London, 10th March. 205-14. DEARMAN, W. R. 1974. Weathering classification in the charac- HERBERT, S. M., ROCHE, O. P. & CARD, G. B. 1986. The value of terisation of rock for engineering purposes in British practice, engineering geological desk study appraisals in scheme plan- Bulletin of the International Association Engineering Geology, ning. In: CULSI4AW, M. G., BELL, F. G., CRIPPS, J. C. & 9, 33-42. O'HARA, M. (eds), Planning and Engineering Geology, Engi- & MATULA,M. 1977. Environmental aspects of engineering neering Geology Special Publication of the Geological geological mapping, Bulletin of the International Association of Society, London, 4, 151-54. Engineering Geology, 14, 141-6. HOLLIDAY, D. W. 1970. The petrology of secondary gypsum DOORNKAMP, J. C., BRUNSDEN,D., JONES, D. K. C., COOKE, R. U. rocks -- a review. Journal of Sedimentary Petrology, 40, 734- & BUSH, P. R. 1979. Rapid geomorphological assessments for 44. engineering. Quarterly Journal of Engineering Geology, 12, HOLLISTER, J. C. & WEIMER, R. J. 1968. General summary and 189-204. conclusions. Quarterly of the Colorado School of Mines, 1-8. DR1SCOLL, R. 1984. The effects of clay soil volume changes on HUMA, J. & RADULESCU, D. 1978. Automatic production of low rise buildings. In: ATTEWELL,P. B. & TAYLOR, R. K. (eds). thematic maps of slope stability. Bulletin of the International Downloaded from http://egsp.lyellcollection.org/ by guest on September 27, 2021

38 F. G. BELL, J. C. CRIPPS, M. G. CULSHAW • M. O'HARA

Association of Engineering Geology, 17, 95-9. of the Seismological Society of America, 25, 1-32. HVORSLEV, M. J. 1949. Subsurface Exploration and Sampling of -- 1956. Elementary Seismology. W. H. Freeman & Co., San Soils for Civil Engineering Purposes. Waterways Experimental Francisco. Station, US Army Corps of Engineers, Vicksburg. RUSSELL, D. J. & PARKER, A. 1979. Geotechnical, mineralogical KNOTT, P. A., DOORNKAMP, J. C. & JONES, R. H. 1980. The and chemical inter-relationships in weathering profiles of an relationship between soils and geomorphological mapping over-consolidated clay. Quarterly Journal of Engineering units -- a case study from Northamptonshire. Bulletin of the Geology, 12, 107-16. International Association of Engineering Geology, 21, 186-93. SEED, H. B., MORI, K. & CHAN, C. K. 1977. Influence of seismic KUSZNIR, N. J., ASHWIN, D. P. & BRADLEY, A. G. 1980. history on liquefaction of sands. Proceedings of the American Seismicity in the north Staffordshire coalfield, England. Society of Civil Engineers, Journal of the Geotechnical Engi- International Journal of Rock Mechanics and Mining Sciences neering Division, 103, 257-70. and Geomechanical Abstracts, 17, 45-55. Sr~EMPTON, A. W. 1970. First time slides in over-consolidated LANE, R. T. 1971. Seismic activity at man-made reservoirs. clays. Geotechnique, 20, 320-24.

Proceedings of the Institution of Civil Engineers, 50, 15-24. -- & HUTCHINSON, J. 1969. Stability of natural slopes and LAWRENCE,C. J. 1978. Terrain evaluation in West Malaysia, part embankment sections. Proceedings of the Seventh International 2- Land systems of south west Malaysia, Transport and Conference on Soil Mechanics and Foundation Engineering, Road Research Laboratory, Report SR378, Department of the State of the Art Volume, 291-340. Environment, Crowthorne. --, SCHUSTER, R. L. & PETLEY, D. J. 1969. Joints and fissures in LEAaTJERMAN, S. P. 1979. Beach and dune interactions during the London Clay at Wraysbury and Edgeware. Geotechnique, storm conditions. Quarterly Journal of Engineering Geology, 19, 205-17. 12, 281-90. SOULE, J. M. 1980. Engineering geologic mapping and potential LILIENTHAL, D. 1944. Tennessee Valley Authority. Penguin, geologic hazards in Colorado. Bulletin of the International London. Association of Engineering Geology, 21, 121-31. McGowN, A., SALDIVAR-SALI, A. & RADWAN, A. M. 1974. TAYLOR, R. K. & SPEARS, D. A. 1970. The breakdown of British Fissure patterns and slope failure in a till at Hurlford, Coal Measures rocks. International Journal of Rock Mechanics Ayrshire. Quarterly Journal of Engineering Geology, 7, 1-26. and Mining Sciences, 7, 481-501. MEAD, W. J. 1936. Engineering geology of dam sites. Trans- VARNES, O. J. 1958. Landslide types and processes. In: ECKEL, E. actions of the Second International Congress on Large Dams, B. (ed.) Landslides in Engineering Practice. Committee on Washington, D.C., 4, 183-98. Landslide Investigations, Highway Research Board, Special MEDVEDEV, S. V. 1968. Measurement of ground motion and Report 29, Washington, 20-47. structural vibrations caused by earthquake. Proceedings of an WALKER, W. n. 1969. Illinois groundwater pollution. Journal of International Seminar on Earthquake Engineering, Skopje, the American Water Works Association, 61, 1, 31-40. UNESCO, Paris, 35-8. WARD, W. H., BURLAND, J. B. & GALLOIS, R. W. 1968. MITCHELL, C. W. 1973. Terrain Evaluation. Longmans, London. Geotechnical assessment of a site at Mundford, Norfolk, for a MITCHELL, J. K. 1986. Hazardous waste containment. In: large proton accelerator. Geotechnique, 18, 399-431. CRIPPS, J. C., BELL, F. G. & CULSHAW, M. G. (eds) Ground- WHITTAKER, B. N. t~ BREEDS, C. D. 1977. The influence of surface water in Engineering Geology, Engineering Geology Special geology on the character of mining subsidence. Conference on Publication of the Geological Society, London, 3, 145-57. Geotechnics of Structurally Complex Formations, Capri. Asso- NlXON, P. J. 1978. Floor heave in buildings due to the use of ciazone Geotechnica Italiana, 1,459-68. pyritic shales as fill material. Chemistry and Industry, 4th WILLIAM SPANGLE AND ASSOCIATES, F. BEACH LEIGHTON AND March 160-64. ASSOCIATES, & BAXTER, MCDONALD AND COMPANY. 1976. NORMAN, J. W. & HUNTINGTON, J. F. 1974. Possible applications Earth-science information in land-use planning- guidelines of photogeology to the study of rock mechanics. Quarterly for earth scientists and planners. United States Geological Journal of Engineering Geology, 7, 107-19. Survey Circular, 721. O'NEILL, M. W. & POORMOAYED, A. M. 1980. Methodology for WILLIAMS, A. A. I. • PIDGEON, J. T. 1983. Evapotranspiration foundations on expansive clays. Proceedings of the American and heaving clays in South America. Geotechnique, 33, 141-50. Society of Civil Engineers, Journal of the Geotechnical Engi- WOOD, N. O. & NEWMANN, F. 1931. The modified Mercalli neering Division, 1116, GT12, 1345-67. intensity scale of 1931. Bulletin of the Seismological Society of PRICE, N. J. 1960. The compressive strength of Coal Measures America, 21,277-83. rocks. Colliery Guardian, 283-92. YAGUE, A. G. 1978. Modern methods used in the study ofrnass

-- 1963. The influence of geological factors on the strength of movements. Bulletin of the International Association of Engi- Coal Measures rocks. Geological Magazine, 100, 428-43. neering Geology, 17, 65-71. RICHTER, C. F. 1935. An instrumental earthquake scale. Bulletin

F. G. BELL, Department of Civil Engineering, Teesside Polytechnic, Middlesbrough TS1 3BA, UK. J. C. CRIPPS, Department of Geology, University of Sheffield, Sheffield S1 3JD, UK. M. G. CULSHAW, Engineering Geology and Aquifer Properties Research Group, British Geological Survey, Keyworth, Nottingham NG12 5GG, UK. M. O'HARA, Department of Geological Sciences, Plymouth Polytechnic, Plymouth PL4 8AA, UK.