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Chapter 1 Introduction J. Charman* & Engineering Group Working Party Cerne Abbas, Dorchester, Dorset, DT2 7JG, UK *Corresponding author (e-mail: [email protected])

framework of the Commission’s current multi-year work 1.1. Deserts programme, the third cycle in 2008 and 2009 focused on desertification and drought. With ongoing climate change, There are several, often conflicting, views of what is a desert. there is a projected shift in arid climatic zones north and In the 1973 edition of the Oxford English Dictionary its defi- south from the mid-latitudes into more populated regions. nition of deserts included the phrase ‘dry, parched, withered, This publication is, therefore, timely in bringing together hence uninteresting’. This somewhat belied the romantic current Earth science and engineering knowledge into a notions in the western world inspired by, among others, state-of-the-art review and handbook for the practitioner. Wilfred Thesiger and T. E. Lawrence. At about this time desert regions became very ‘interesting’, gaining a greater 1.1.1. Definitions significance with the rising price of oil fostering a develop- ment boom in many oil-rich countries, especially in the Many definitions have been proposed for the term ‘desert’ and Middle East. these are considered indetail inChapter 2.In general, most dic- During this period early western designed and controlled tionary definitions refer to regions that do not produce suffi- building and construction projects in the Middle East cient vegetation to support a human population. Many maps began to fall foul of a number of geotechnical hazards depict the location and extent of the deserts of the world. little understood by professionals whose previous experience Table 1.1 contains a list of the major, non-polar, deserts of had been gained in the temperate regions of the world. Tra- the world (after Goudie 2002) and the numbers shown in the ditional, locally developed techniques were neglected or table relate to the location shown on the map (Fig. 1.1). ignored, as had reported knowledge from valuable experi- While the location of, for example, the Sahara, Gobi and ence in the field (Bagnold 1941). Atacama deserts are well known, in reality they cover a Over the last 30 years considerable understanding and range of climatic conditions. For this report, which considers experience has been gained of the geomorphological pro- the physical characteristics of deserts and their influence on cesses and ground characteristics peculiar to desert engineering behaviour, a climatological definition has been regions, and their effects on design and construction. Many considered to be the most useful basis for the description innovative engineering techniques have been developed and identification of hot deserts. and employed, and information on these advances is now In detail, climate is unique to location and depends on the widely disseminated in the technical literature. local interaction of several factors, including temperature, The report of a Geological Society of London Working precipitation, relative humidity and wind. In any one geo- Party on Tropical Residual Soils (Fookes 1990, 1997) was graphically discrete desert, it is difficult to define transitions the first to consider a particular environment as the focus from typical desert conditions into other climatic regimes for an engineering geological handbook. As a natural succes- related to changes in latitude and elevation. sor in this approach, this Working Party report on engineer- Most scientific classifications rely on some combination ing works in Hot Desert regions, commissioned by the of the number of days of rainfall, the total amount of Engineering Group of the Geological Society, is intended annual rainfall, temperature, humidity or other factors. The to provide, under one cover, a practical handbook for the most widely accepted system, however, is probably that of practitioner, academic and student working in this sector Meigs (1953), dividing desert regions into three categories (see Text box 1.1). according to the amount of precipitation they receive. In 2003 the United Nations General Assembly, in its res- Meigs’ assessment used the Thornthwaite (1948) Moisture olution A/RES/58/211, declared the year 2006 as the Inter- Availability Index, and the Aridity Index as another measure. national Year of Deserts and Desertification. Combating These are explained more fully in Chapter 2. Typically, desertification and drought has been discussed by the UN extremely arid lands have at least 12 consecutive months Commission on Sustainable Development and, in the without rainfall, arid lands have less than 250 mm of

From:M.J.Walker (ed.) Hot Deserts: Engineering, Geology and Geomorphology – Engineering Group Working Party Report. Geological Society, London, Engineering Geology Special Publications, 25, 1–6. http://dx.doi.org/10.1144/EGSP25.01 # The Geological Society of London 2012. Publishing disclaimer: www.geolsoc.org.uk/pub_ethics Downloaded from http://egsp.lyellcollection.org/ byguestonSeptember25,2021

Fig. 1.1. Distibution of the major non-polar deserts of the world (after Goudie 2002). The numbers relate to the list of locations shown in Table 1.1. Downloaded from http://egsp.lyellcollection.org/ by guest on September 25, 2021

2 INTRODUCTION

Text box 1.1. Terms of Reference of the Working Party

(1) These Terms of Reference are as agreed by the Desert Working Party (DWP) and committee of the Engineering Group of The Geological Society of London. (2) The DWP has been established by the Engineering Group of the Geological Society and comprises officers and specialist participating members who will act as chapter authors or co-authors. The participating members may be assisted by any number of corresponding members based in the UK and, occasionally, overseas. (3) The DWP will produce a report to complement the earlier report on Tropical Residual Soils produced by an earlier Working Party of the Engineering Group, first published in 1990 and re-published in book format in 1997. It is currently envisaged that the report will be in book format, but this will be kept under review in recognition that major change is taking place within the publishing industry. (4) It is intended that the report will be a comprehensive, state-of-the-art, review on hot deserts and their materials. Primarily, the report will cover conditions and materials in modern hot deserts, but there will be some coverage of unmodified ancient desert soils that exhibit engineering behaviour that is in many respects similar to modern desert materials. (5) The aim of the DWP is to produce a report that will act as an essential reference handbook for professionals as well as a valuable textbook for students and others. The style will be concise and digestible by the non-specialist, yet be authoritative, up to date and extensively supported by data and collations of technical information. The use of jargon will be minimized and necessary specialist terms will be defined in an extensive glossary. There will be copious illustrations, many of which will be original, and many good-quality photographs. (6) The content of the report will embrace a full range of topics, from the latest research findings to practical appli- cations of existing information. There will be an endeavour to identify likely directions of future research and to predict future development. The report will be based on worldwide experience in hot desert terrain, and will draw upon the experience of its members and publications on hot desert conditions. (7) There will be collective responsibility for the whole report. Although each participating member will be the draft- ing author or co-author of one or more chapters, all members will be expected to review and contribute to the chap- ters drafted by other members.

annual rainfall, and semi-arid lands have a mean annual pre- that are relevant to such deserts today. In these regions, the cipitation of between 250 and 500 mm (Table 1.2). influence of surface water is mainly experienced only in An initial subdivision can be made into ‘cold’ and ‘hot’ ‘rare’ events, such as flooding. The effect of moisture move- deserts. In ‘cold deserts’, in the higher latitudes, the prevail- ment is generally limited to those areas with near-surface ing low temperature and the low moisture availability are the groundwater, such as inland drainage basins and coasts. causes of the lack of vegetation. In ‘hot deserts’, in the mid- Nevertheless, it is essential that in these areas the process latitudes around the tropical belts, the lack of vegetation is be clearly understood to ensure the safety and durability of the result of a combination of high temperature and aridity, new structures. where evaporation is largely in excess of precipitation and In semi-arid and dry sub-humid deserts, the role of moist- overgrazing. The word ‘desert’ can cover, therefore, a ure increases; for example, in the formation of pedogenic range of climatological conditions from arid to dry sub- soils. Indeed, many features of present-day hot deserts are humid and from hot to cold. This raised the conundrum for relict, and are the result of moisture movement processes the Working Party of where to focus this report since it more active in the mild semi-arid and dry sub-humid con- was considered that to attempt cover the complete range of ditions that have occurred repeatedly in the fluctuating cli- conditions could weaken its application. To avoid this it matic cycles (glaciations) of the Quaternary. Similarly, the was decided to concentrate the Working Party’s efforts on present-day cool, cold or polar deserts also encompass pro- hot desert regions. cesses of a periglacial, or even glacial, nature. These con- ditions often make significant differences to local materials and the engineering approach. 1.1.2. Scope of this report: hot deserts While Chapter 2 provides a comprehensive review of the distribution and range of desert conditions, to attempt to This report is focused primarily on the ‘hot’ mid-latitude arid address the conditions experienced across the entire range and hyper-arid deserts, and the characteristics and processes of desert environments in subsequent chapters would Downloaded from http://egsp.lyellcollection.org/ by guest on September 25, 2021

INTRODUCTION 3

Table 1.1. The major non-polar deserts of the world* (after Goudie 2002)

Desert Location Desert Location

1 Arabian Egypt 23 Monte Argentina 2 Atacama Chile 24 Namib South Africa, Namibia, Angola 3 Chalbi Kenya 25 Negev Israel, Palestine 4 Chihuahuan Mexico, USA 26 Nubian Sudan 5 Colorado USA 27 Ogaden Ethiopia 6 Cholistan India 28 Ordos China 7 Danakil Ethiopia, Djibouti 29 Patagonian Argentina 8 Darb el Arba’in Egypt, Sudan 30 Peruvian Peru 9 Dzungarian China 31 Registan Afghanistan 10 Eastern Egypt 32 Rub’ Al Khali Saudi Arabia 11 Gibson Australia 33 Sahara North Africa 12 Gobi China, Mongolia 34 Sechura Peru 13 Great Basin USA 35 Simpson Australia 14 Great Sandy Australia 36 Sind Pakistan 15 Great Victoria Australia 37 Sturt Australia 16 Kalahari Botswana, S. Africa, Namibia 38 Strezlecki Australia 17 Karakum Turkmenistan 39 Syrian Middle East 18 Karoo South Africa 40 Taklimakan China 19 Kyzylkum Uzbekistan, Kazakhstan 41 Tanami Australia 20 Libyan Libya, Egypt 42 Thal Pakistan 21 Lut Iran 43 Thar India, Pakistan 22** Mojave USA 44 Turkistan Turkmenistan

*The numbers shown relate to the desert locations shown on the map in Figure 1.1. **In addition, the Sonoran desert is to the south of the Mojave in the USA and extends southward into Mexico to the Baja California and the eastern side of the Gulf of California. provide too wide a subject and dilute the impact of the usefully interpolate between the processes described in this volume. This report therefore covers the hot desert report and those in the Tropical Residual Soils report. For ‘extreme’, as exemplified by the deserts of Australia, North the cooler deserts, similar interpolation will be required Africa, the Middle East and SW USA (Fig. 1.1). For semi- with published material on glacial and periglacial processes. arid and dry sub-humid regions, the reader can Chapter 4 sets out the basis for developing a desert geo- model, which forms an essential framework to the whole document. The practitioner can use the conventional Table 1.2. Classification of deserts according to aridity (after landscape-based classification to establish the nature of the UNEP 1992) terrain and associated hazards relevant to a project, while the geospecialist can use the Earth systems approach – Aridity Rainfall Aridity Index Thornthwaite (mm year21) Moisture whereby the desert-related processes can be identified, characteristics Availability assessed and evaluated. These identify a series of landforms, Index each with associated hazards. Parts of the stratigraphic column contain soils and rocks Hyper-arid ,25 (12 months or ,0.05 ,2 40 longer without that originated or were subsequently modified in a desert rain, i.e. 100% climate; for example, Permian and Triassic in the UK. annual These fossil desert materials are not discussed in detail but variability) their potential behaviour in certain engineering situations Arid 25–250 (low 0.05–0.20 ,2 40 rainfall 50– may reflect their desert origins and this report should assist 100% annual in identifying the potential effects of their relict properties. variability) Semi-arid 250–500 (seasonal 0.20–0.50 220 to 240 rainfall, 25– 1.1.3. Engineering significance of the hot desert 50% annual environment variability) Dry sub-humid (reliable seasonal 0.50–0.65 .2 20 Extreme arid and hyper-arid desert environments present rainfall, ,25% a range of unusual problems for construction and engineer- annual variability) ing. These are discussed more fully in subsequent chapters but, in summary, include: Downloaded from http://egsp.lyellcollection.org/ by guest on September 25, 2021

4 INTRODUCTION

1.1.3.1. Major sand dunes loading because they were deposited in an edge-to-edge par- Many sand seas that contain active and relict dunes, which ticle arrangement. Many desert clay soils possess a chlorite, can reach up to more than 100 m in height. The identification attapulgite (also known as palygorskite) or smectite clay of the non-mobile part of the dune sequence is necessary so mineralogy and can undergo significant volume change on that any long-term problems of additional loading, loss of wetting or drying. Differential settlement due to shrinking support or differential settlement caused by sand movement clay soil can result from changes in moisture content. are avoided. In areas of sheet sand and mobile dunes, winds transport sand to accumulate against natural and man-made 1.1.3.5. Karst obstructions, and abrasion damage can be significant. Pro- Both carbonate- and sulphate-rich rocks have been prone to blems of trench infilling, equipment damage and temporary dissolution during periods of more humid climate and higher blocking of access can be experienced. Thick sheet sand sur- groundwater levels. This has left a legacy of minor karst (i.e. faces and dunes also present difficulties for traffic. The threat solution) features, including enclosed surface depressions to buildings, pipelines, transport networks and cultivated (dayas), small subterranean caverns and pitted surfaces. land in many desert regions is severe and calls, in some The potential presence of solution-widened joints or cave cases, for extensive control measures. These include the systems presents a risk of collapse and loss of structural use of surface protection measures to minimize sediment support. removal (e.g. gravel spreading, surface sealing), careful building design to reduce abrasion damage and dust 1.1.3.6. Stone pavements ingress, and the erection of wind breaks to prevent sand A common feature of many deserts is a single layer of transport. The problems of sand and dust erosion are not angular or subrounded gravels immediately above stone-free limited to desert regions as wind-blown silts and clays poten- material that covers many desert pediments and plains. tially can be transported many thousands of kilometres from Although stone pavements provide excellent surface protec- their site of initial entrainment (Goudie & Middleton 2001). tion against wind and water erosion, they are easily destroyed by vehicle traffic, leaving them susceptible to 1.1.3.2. Dissected terrain wind and water erosion. Long-term surface lowering and dissection of uniform Paradoxically, it is surface water and groundwater that plateau surfaces (e.g. etch plains) has created ‘multi-level’ present some of the greatest geohazards. landscapes where erosional remnants (mesas, buttes and The nature of desert precipitation means that drylands are low terraces) rise above the general plain level. Careful periodically affected by major storm events, leading to routing of linear projects is required through this type of surface water and sediment movement that results in terrain in order to maintain an acceptable alignment and to serious soil erosion, slope failure and extensive flooding. minimize excavation volumes. ‘Badlands’ topography rep- The hazard is compounded by the fact that such events are resents the extreme, and the most cost-effective solution is unpredictable and that there is little information on flood often to avoid such areas altogether. magnitudes, frequencies and sediment transport rates for many parts of the world. This means that the possibilities 1.1.3.3. Indurated horizons (duricrusts) for conflicting predictions or serious underestimates of Indurated horizons present at or near the ground surface can flood magnitude are considerable (Cooke et al. 1982). cause excavation problems. They generally form through the Most parts of the desert surface can experience shallow accumulation of calcium carbonate (calcrete), silica (sil- sheetflows but flooding can trigger a number of problems. crete), gypsum (gypcrete) or iron (ferricrete), by evaporation It can initiate collapse of dayas or initiate collapse or during past wetter climate phases. Calcrete is a common volume change in metastable soils. It can wash away road feature of deserts, with extensive carbonate-rich horizons embankments, bridge abutments and other on-ground engin- occurring, for example, across the Eastern Desert. Silcrete eering structures, including domestic housing. It can also is formed through the accumulation of silica, creating a provide the moisture to mobilize aggressive salts. brittle, intensely indurated material comprising quartz clasts cemented by crystallized or amorphous silica. Generally, the 1.1.3.7. Salinity higher topographical levels are the oldest, and tend to be Salinity, associated with high groundwater levels and high covered by the thickest, strongest and most-developed duri- rates of evaporation where the capillary fringe is close to crust layers; while the lower levels may only have a thin and the ground surface, causes deposition of salts within the discontinuous cover of weak or moderately weak material. soil profile. Salts can also accumulate in soils through the Duricrusts may also be present as layers ‘floating’ within a deposition of dust resulting from the deflation of base level sequence representing breaks in the depositional history of plains. The principal salts of concern are chlorides and sul- the material. phates. In dry conditions, roads and foundations need not suffer ill effects; but, if the soils are allowed to become 1.1.3.4. Metastable soils moist, the mechanism is set up for solution, transport of Unless well cemented, some wind-blown silt or sand-sized salt in solution and precipitation. Salts can be introduced desert soils (aeolian deposits) can collapse on wetting and into structures or roads internally, through the contamination Downloaded from http://egsp.lyellcollection.org/ by guest on September 25, 2021

INTRODUCTION 5 of aggregates prior to construction, or externally via water distribution of the report in parts to suit the reader, it was seepage and/or capillary rise. Salt weathering can result in considered important that each part fairly represents the col- numerous problems ranging from superficial damage to lective authorship. Each chapter is therefore assigned building stones to cracking and scabbing of surfaced roads, a principal author(s), while the importance of the input and even serious failures of concrete structures (Cooke from the additional Working Party members is clearly et al. 1982) (see also Chapter 10). acknowledged. The continued growth of desert urban centres can only serve to increase the potential human contact with geoha- zards, such as catastrophic runoff events and aggressive 1.2.2. Objectives groundwater conditions, and may also lead to the destabili- The aim of the Engineering Group Working Party of the zation of desert surfaces making them more vulnerable to Geological Society was to establish an authoritative compre- wind erosion. Many cities, even if remote from deserts, are hensive state-of-the-art review of the geomorphological pro- experiencing the effects of desertification in the form of cesses prevalent in desert regions, the characteristics and wind-blown dust; for example, Beijing. However, with a behaviour of desert soils and rocks, appropriate ground greater appreciation of the nature of the geomorphological investigation and testing techniques and guidelines on the processes and ground-surface conditions likely to be availability of natural construction materials and on engin- encountered in desert environments, potential challenges to eering design and construction methods. This has been set construction can be predicted and mitigated. within the framework of a series of models, which allow the practitioner to identify the facets of the desert environ- ment relevant to his/her involvement and proceed appropri- 1.2. The Working Party ately through the project cycle.

1.2.1. Membership 1.3. Structure of the report: contents A steering committee was convened in early 2003 by the Engineering Group of the Geological Society to consider Based on the objectives outlined in Section 1.1.2, the report the formation of a Working Party to prepare a report on is published as a book which has been structured so that the the engineering geology of hot deserts, which would comp- chapters are grouped into three main themes: Geological and lement that already published on tropical residual soils. The Geomorphological Background, Chapters 2–4; Investi- steering committee, chaired by Professor Peter Fookes, was gation and Testing – Objectives and Procedures, Chapters asked to determine the scope of the work, draft the likely 5–7; and Engineering Behaviour, Chapters 8–10. structure of the report and identify prospective members of The Geological and Geomorphological Background chap- the working party. ters introduce the scientific concepts of the world’s desert The first meeting of the Working Party, chaired by Mr regions. Alternative definitions are reviewed followed by a John Charman, was held in November 2003. Members of description of the factors that contribute to all desert environ- the Working Party were drawn from persons with known ments – geology, climate and human impact. The weathering desert experience, from academics, researchers, consultants process in desert regions is described together with the influ- and contractors, including geomorphologists, engineering ence of wind, water and, in particular, the role of subsurface geologists and civil engineers. After initial discussions water in providing salty aggressive ground conditions. The within the Working Party, members were allocated a respon- final chapter in this theme develops the use of models to sibility for drafting specific chapters, relevant to their indi- identify the relevant processes and controls – initially from vidual expertise. The chapters were subsequently subjected desk study information and then refined to be site specific to extensive iterative review and comment from the whole by pertinent ground investigation. Pre-existing models have Working Party. An important part of the review process been based on a landscape classification. In this report the was the use by the chapter authors of advice and review by models are based on an Earth systems approach, whereby external corresponding members who are listed in the the rock cycle is influenced by processes that are azonal acknowledgements. A presentation of the work completed and by those that are specifically desert related. These to date was made at the International Association for Engin- produce a series of landforms, each with associated hazards. eering Geology Congress in Nottingham, UK in 2006, which The Investigation and Testing – Objectives and Pro- provided further opportunity for comment from the wider cedures chapters take a logical, staged path through the technical community. investigation cycle, initially considering the description The Report is a team effort, each chapter benefiting from and classification of desert soils and rocks. Existing the input of the Working Party as a whole. This is the first schemes for carbonate materials and desert soils and rocks Working Party Report, published as an Engineering are reviewed, and a classification is recommended. In the Geology Special Publication, to use electronic publishing. desk study chapter, the opportunity has been taken to Since this form of publication encourages separation and review the latest developments in the rapidly changing Downloaded from http://egsp.lyellcollection.org/ by guest on September 25, 2021

6 INTRODUCTION

field of remote sensing technology and methods. Conven- detail by all the Working Party members during a series of tional methods of ground investigation in desert regions face-to-face meetings over several years. The chapter thus carries need special adaptation to be able to provide representa- the collective authority and is the collective responsibility of the tive samples of granular soils in an environment where whole Working Party, the membership of which is shown on pre- drilling water is scarce. Moreover, the use of water may liminary page xvi of this volume. compromise the level at which chemical test results can be taken as representative of the material from the in situ material from which samples are taken. Appropriate tech- niques for investigation and sampling in desert soils and References rocks are emphasized. Bagnold, R. A. 1941. The Physics of Blown Sand and Desert The Engineering Behaviour chapters consider the avail- Dunes. William Morrow & Co., London. ability of natural construction materials, their location, Cooke, R. U., Brunsden, D., Doornkamp,J.C.&Jones,D.K.C. extraction and processing requirements, and their suitability 1982. Urban Geomorphology in Drylands. Oxford University for engineering use. The mechanics of the engineering be- Press, Oxford. haviour of desert soils and rocks places emphasis on collap- Fookes, P. G. (ed.) 1990. Tropical Residual Soils Geological sible and partially saturated materials, and examines the role Society Engineering Group Working Party Report. Quarterly of salt in influencing soil behaviour. Finally, guidelines are Journal of Engineering Geology, 23, 4–101, doi: 10.1144/ GSL.QJEG.1990.023.001.01. provided for the consideration of designers and for construc- Fookes, P. G. (ed.) 1997. Tropical Residual Soils: A Geological tion issues in the use of desert materials or for engineering in Society Engineering Group Working Party Revised Report. a desert environment. Geological Society, London, Professional Handbooks. There is an Appendix to Chapter 7 – ‘Laboratory and in Goudie, A. S. 2002. Great Warm Deserts of the World: Landscapes situ testing procedures’ – that provides a summary of the and Evolution. Oxford University Press, Oxford. special test methods applicable to desert regions and Goudie,A.S.&Middleton, N. J. 2001. Saharan dust storms: where they may be sourced. Towards to end of the book nature and consequences. Earth-Science Reviews, 56, there is an appendix (Appendix A) that contains a detailed 179–204. Meigs version of the desert model referred to in Chapters 4 and , P. 1953. World distribution of arid and semi-arid homocli- mates. In: Reviews of Research on Arid Zone Hydrology. Arid 5. A glossary of some less familiar geological terms, for Zone Research Series, 1. UNESCO, Paris, 203–209. engineers, and engineering terms, for geologists, is provided Thornthwaite, C. W. 1948. An approach towards a rational classi- at the end of the book. fication of climate. Geographical Review, 38, 55–94. UNEP 1992. World Atlas of Desertification. Edward Arnold, This chapter is an integral part of the report ‘Hot Deserts: Engineer- Sevenoaks. ing, Geology and Geomorphology’. Although the above-cited UNITED NATIONS GENERAL ASSEMBLY 2003. Resolution A/ authors drafted the chapter and played a main part in its research RES/58/211. International Year of Deserts and Desertification, and development, every chapter was reviewed and revised in 2006. United Nations, New York.