3 8 3

勿 R A E llison, S J B ooth and P J Strange G eological m apping in urban areas The B G S exp erience in London

B ased on a p ap er p resented at the International C onference on G eoscience in U rban D evelop m ent (L andp lan IV) 11- 15 A ugust 1993, B eijing, C hina

The B ritish G eological Survey has established the tively leading to better interpretation of ground conditions and pre- L O C U S (L O ndon C om p uterised U nderground and Sur- diction of potential geological hazards. H ow ever, the potential value of sound geological know ledge in underpinning planning and urban face) geological p roject, w hose aim is to p rovide geo- regeneration issues has been largely underplayed, and the benefits of logical m ap s and interp reted datafor London. The resul- detailed understanding of the relevant geological factors, for the tant high-quality m odel has alrea办 p roved valuable in m ost part, have not been fully realised. C ostly rem edial w ork during con s tr u ction caused by unfore- p rojects rangingf rom the site-specif c to strategic over- seen geological factors is not uncom m on in the L ondon region, and v ie i认 the variability of strata below London has been a source ofe ngineer- T h e p erceived requirem entfor geological inform a- Ing difficulty dating back to the first tunnel under the Tham es, built tion in urban areas is to supp ort land-use p lanning, by B runel in 1825. N ow , after careful study of the geology and the processes that have laid dow n the different deposits, there are expla- environm ental m atters, p roject p lanning and civil engi- nations for the form erly "m ystifying，， changes of rock type beneath neering. W ith increasing dem and for urban geoscience L ondon and m any of their variations can be predicted. inform ation, the Survey has develop ed a geologically T he statutory fram ew ork under w hich developm e n t can take place in B ritain puts the onus on local authorities to ensure that a attributed digital m ap-production system . This system is physically safe environm ent is established, and it is a developer's structured to p rovide, on dem and, up-to-date colour- responsibility to clean up contam inated sites. T his m eans that the p rinted geological m aps at any scale. Them atic m aps planning process m ust take account of the risks that geological haz- ards m ight pose. In the London area these hazards include landslip, illustrating sp ecif c asp ects of geological data are pro- dissolution subsidence, chalk-m ining subsidence, ground heave, duced also. The output is m ade available in hard-copy com pressible strata, high groundw ater and rising groundw ater, and digitalform for G IS applications. derelict w orked ground, landfill sites and landfill gas, and high-sul- A dditionally, a digital relational da ta base has been phate groundw ater. The perceived requirem ent in rapidly developing and regenerating urban areas, therefore, is for geological inform ation established using inform ation from 20,000 borehole rec- to support land-use planning, environm ental m atters, project plan- ords for L ondon. B orehole site data and levels, the base ning and civil engineering. The L O C U S (LO ndon C om puterised of m an-m ade ground and three key geological horizons U nderground and Surface) geology project w as established to m eet this requirem ent. T he project is concerned w ith m aking new geolog- are usedfor three-dim ensional com p uter m odelling. F or ical m aps and com puterised geological m odels of L ondon and the L ondon, these horizons are the base of the sup erfi cial deposits, w hich are essentially the sedim ents dep osited F igure L - London and the surrounding region. 勿 the R iver Tham es; the base of t he L ondon C lay, w hich

underlies m uch of London and is the best tunnelling 10 2 0 km s m edium ; and the top of the C halk, an im p ortant aqu旅r 砂let1 L- ea1) in the London B asin. Im plem entation of digital m ap V -1〕／ production and the rationalisation 以 p rincip ally, bore- hole ii响rm ation has enabled routine p roduction of c om - 朋 puter-generated geological m odels of London and pro- 。 vided the m eans to visualize autom atically a range oJ 司古 司 inform ationf rom point data to 3-D m odels. 孙 毛公内白0 内人 YkkkES 13ARFIAGE LA C K W A LL T U N N E L W IN D S O R 褚认轰竺 P U R F L EE T In tro d u ctio n ＋ 产牲 :-:-A 3A T T E R S E A ： T he London region, with。population in excess of 6.3 million, is one of the m ajor conurbations in w estern Europe. T he processes of 街介少 份T呼}} ORRIDOR planning and developm ent in the region, in com m on w ith all urban areas, can benefit from a know ledge of the ground conditions w hich 犷 are encom passed in geological inform ation. Such inform ation, w hen 才 used appropriately, w ill ultim ately result in cost benefits by effec-

Episodes, Vol. 16, no. 3 3 8 4

surrounding region (figure 1). T his w ork utilises recent advances w ith lim b dips generally less than 2'. In central and southeast Lon- m ade by the B ritish G eological Survey (B G S) in the developm ent of don sm all periclines, w ith axial-plane traces roughly parallel to the digital borehole databases and digital production of geological m aps m ain synchne and with limb dips up to 5', are superim posed on the and draw s heavily on the w ide range of geological expertise and larger structure. T he C halk crops out around the m argins ofL ondon, experience of the Survey staff. form ing the relatively high relief (over 130 m above sea level) of the T he project w as set up w it h t h ree m ain aim s and objectives: ．to produce geological m aps of London at scales of 1:10,000 and 1:50,000 Nfsoeordr eitmhxae Dmnotpswl wens Per uaernfl doe Cledthe idnlt etwhrineth eH atihslltes a C,n ahdnad Il一nian ntdhdseo f croo irrnme tsh th oeef w sceosmrte.e Po pafel tarhieceol Ligneoense-, ．to establish a digital relational borehole database don B asin (figure 3). Few faults are know n, the principal ones being norm al, w ith a curving northeast trend. M inor flexures in structure ．to produce com puter-generated geological m odels of the m ain contours suggest also northw est-trending flexures or faults. sub surface ro ck un its. In early to middle Quaternary (Pleistocene) times, a rive r a n臀 － tral to th e T h am es fl o w ed no rtlleastw ard to tn e no r h or L o nu on (G ibbard, 1985). D uring the A nglian stage, som e 350,000 years ago, G eology of L ondon a m ajor ice sheet advanced southw ard across B ritain as far as the northern part of the L ondon region, leaving a till deposit w hich has T he London region lies astride the valley of the River Thames on subsequently been dissected. T his ice sheet blocked the valley of the C retaceous C halk and unlithified Palaeogene clays and sands. T he ancestral Tham es (G ibbard, 1977), diverting the river to its present overlying superficial deposits principally consist of Q uaternary course. Subsequently, fluvial sands and gravels assigned to seven gravels laid dow n by the T ham es. river terraces have been deposited in the I 0-km -w ide present valley. T he C halk w as deposited acro s s t he entire region. It w as folded They are about 2 to 5 m thick and overlie benches cut largely in L on- and eroded, leaving about 220 m thickness in the London region, don C lay, form ing broad, m ore-or-less flat, tracts of land on w hich m o-t nf ei-m trM L ondon is situated (fiRure 4). prior to deposition of the Palaeogene strata. T he P alaeogene sequence, up to 180 m thick, w as laid dow n at the m argin of the con- tem porary N orth Sea and records a succession of transgressive enndeedD黔玺搬忽紫esveean-lseivane)l忠丫念nBdr i1ta0i0n 1mw ehtircehs events caused largely by eustatic sea-level changes. T he low est beds low er than the present level. D uring this period the Tham es in the (T hanet Sand F orm ation and U pnor F orm ation) are m ainly shallow London region cut dow n to a m axim um of 15 m below present sea m arine sands. They are succeeded by brackish-w ater sands and level. T he subsequent rapid sea-level rise in the H olocene led to lagoonal clays (W oolw ich Form ation) and alluvial m uds,that w ere ilnofiwlsli"n gno o fm tohries tvhaalnle y0．.a5 n kdrn th ien deivameloetpemr tehnatt o efro lodceadli uset)d to "s 5c0ou mr hinotlo- subjected to pedogenesis (R eading Form ation). A nother m arine transgression led to the deposition of a thick succession of m arine bedrock (figure 5). The precise tim ing and m echanism of scour for- m uds (L ondon C lay Form ation) w hich grade into shallow er-w ater m ation and infilling is uncertain, but both the presence of ground ice m arine sands (B agshot Form ation). A generalised succession of and the effect ot hydrostatic pressure in the C halk have been sug - these beds is show n in figure 2. gested as possible causes (B erry, 1979; H utchinson, 1980). T he geological structure of th e region is relatively sim ple, being T he present R iver Tham es is tidal through L ondon, ret a in e d by dom inated by a broad southw est-to-northeast-trending syncline (the artificial flood em bankm ents on a floodplain of alluvial deposits less L ondon B asin), flexed during the A lpine orogeny in M iocene tim e, th an 0 .5 k in w id e in the w est and 3 kin in th e east.

Figure 3.- Simplif ed geol09Y and cross-section of the London region. F or key to the geologicalf orm ations seefi gure 2.

1 0 2 0 k m 一 － 一 一 － － 一 －－副 N 六 凸 1 本 e

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鼠黑 阅川卜．． 一拼清珠福SAND FORMA｛1ON童 撰

二任任任母L O N

山 N 山 司川卜．． 口 0 R E A D IN G W O O L W IC H 山 哎 F O R M A T IO N F O R M A T IO N ︺ 咬 d U P N O R F O R M A T IO N LO W ER C R ET A C E O U S S T RA T A F 仓ure 2.- G en er- alized geological T H A N ET S A N D F O R M A T IO N succession, not to S N R iv er T ha m es ｜ 司门p - scale, in the L on- don region. A rrows + l o o m s in d ica te th e stra ti- S e a le v e l grap hic position of 一1 00 m s geological surfaces en tered in to th e com puter database

Septem ber 1993 了8 5

through w ater-saturated ground or cutting through unconsolidated 1 0 2 0 km str a ta . N G ro u ndw ater problem s increase w ith depth, particularly w here A 早 excavations encounter the W oolw ich and R eading form ations, 十 ｜ w hich underlie the L ondon C lay, as in an estim ated 23 krn ofL ondon 1 ． U nderground railw ay tunnels (C raig and Sim pson, 1990). Tunnel ‘ lining usually consists of cast-iron segm ents or reinforced-concrete segm ents, w ith m odern practice favouring concrete segm ents expanded into close contact w ith the rock strata. The presence of } ,2 a pyrite and gypsum , particularly in the London C lay and in places in 祥：一尸 只 the other Palacogene form ations, has locally increased the sulphate 月 (':1 ， lr} v and sulpburic acid levels in the groundw ater, and som e reaction has taken place w ith tunnel linings. This problem of acidic groundw ater L 沁ND OI- Y W ' '叮 in contact w ith concrete structures is likely to be exacerbated in the future, as the w idespread cessation of w ater abstraction from deep boreholes is causing groundw ater levels in central London to rise at ：：：：：一器之奥呼艺 a rate of up to I in annually. 飞 L ondon C lay has a m ed i u m -to-high shrinkage potential (D ris- 一：一：一：孰丈玉 L IN E O F S EC T IO N coll, 1983) and this is reflected in the relatively high incidence of subsidence recorded from properties sited on London C lay, m ost of 口 w hich lie w ithin the suburban belts surrounding London. Follow ing T ill 口(b o u ld er c la y ) the serious drought in the sum m er of 1976, w idespread structural R iv e r te rrac e dam age w as recorded from buildings sited on London C lay, and as a d ep o sits consequence building regulations w ere m odified to ensure that typi- cal house foundations w ere increased in depth. In the L ondon area, landslipping is a geol o g ic al hazard m ainly on L ondon C lay slopes, particularly in the sandier upper part of the N form ation w here springs are com m on and w hen these hillslopes are greater than 7'. It is not unusual for there to be m inor landslips on m an-m ade slopes such as railw ay cuttings through London C lay, m any years aft er excavation. R iv e r T ha m e s Subsidence into dissolut io n hollow s and m an-m ade w orkings is S a w ell-know n geological hazard affecting the C halk outcrop and ｝＿ areas w here the top of the C halk is near the surface. The severe storm surge of 1953, w hich flooded m a n y parts oft he east coast of E ngland and areas of L ondon, em phasised the need to protect low -lying ground by strengthening sea defences in the region. The m ajor elem ent in this strategy w as the T ham es B arrier (figure 1), Figure 4- D istribution of thep rincipal superfi cial deposits on w hich is a structure com prising m ovable gates that can be closed th e London region, and g eneralized cross-section. w hen exceptionally high tides are expected (W akeling and Jennings, 1979). It extends across the T ham es at W oolw ich R each. Essential to the success of the project w as the im provem ent of the sea-defence em bankm ents bordering the T ham es dow nstream of the barrier. C on- G eological hazards and engineering cerns. about global w arm ing and rising sea levels, linked w ith the pos- sibility that southeast England is gradually sinking, have increased practice the aw areness of the long-term risk of flooding. T he London Clay is。。excellent tunnelling medium, which greatly facilitated the rapid developm ent of London's 656 kni of tunnels. O w ing to a variety of m an-m ade and geological factors, it w as, how - D igital geological m ap developm ent ever, often difi cult to confi ne the tunnels to the London C lay strata M any of the unforeseen engineering problem s that arose in the T he earliest systematic geological mapping of London was carried course of tunnelling beneath London have resulted from a failure to oanutd b tyhe th re sGueltosl owgeicreal翔visehye idn a thse d e1s8c6r0ipst iavte o nmee imnochirs to ( Wonheit makieler, 黑cnt ucmorbrecrt loyf t hocec raoscikohnes,a dex lecvaevla (tboarsse h oafvte h en scuopuenr黑dthepeo rsoictsk)-. 1872; 1889). B etw een 1900 and 1930, surveys at six inches to one head surface w hilst tunnelling through L ondon C lay, and several m ile (1: 10,560) led to four one-inch m aps (sheets 256, 257, 270 and hundred cubic m etres, of gravel and w ater have been flushed into the 271) and their respective descriptive m em oirs (B rom ebead, 1925; tunnel, creating serious subsidence cavities at the surface. T unnel- D ines and Edm unds, 1925; D ew ey and B rom ehead, 1925; D ew ey, ling beneath the T ham es required particular precautions to prevent B rom ehead, C hatw in and D ines, 1924) that covered the w hole of river w ater from flow ing in and flooding the excavations. The "scour greater L ondon (figure 1). hollow s" that penetrate far below the predicted upper surface of the W ith the increasing d e m a nd for urban geoscience inform ation, L ondon C lay can usually be recognised during detailed site investi- B G S has developed a digital m ap-production system (N ickless and gations prior to engineering developm ent, but som etim es even very Jackson, 1993). T he first digitally produced m aps at 1:10,000 w ith dense borehole coverage has m issed localised depressions, w hich full geological attribution are now available for the N orth L ondon area. T he current project w ill com plete digital cover for the w hole of are described by engineers as "funnelling dow n". Such deep drift - filled hollow s w ere encountered in the course of a num ber of tun- L ondon, including the E ast T ham es C orridor (figure 1). This corri- nelfing projects and m ajor building developm ents, for exam ple at the dor is an im portant area for developm ent, w hich is likely to be stim - B attersea P ow er S tatio n and th e B lackw all ro ad tu n nel. C h em ical ulated by infrastructure im provem ents associated w ith the im m inent consolidation m ethods, ground-freezing techniques and w orking opening of the C hannel Tunnel linking E ngland and France and the under com pressed air have been invaluable aids w hen excavating proposed high-speed rail connection w ith London.

Episodes, v. 16, no. 3 3 8 6

T h e digital m ap system holds geologically attributed (or vec- torised) spatial inform ation. It can routinely produce on dem and up- D igital borehole database to-date colour-printed geological m aps at any scale. Im portantly, the attribution of geological inform ation facilitates the production of T he Project has established。digital, relational borehole database. them atic m aps illustrating com binations of geological and non-geo- T his digital resource is founded on the paper records of w ells and logical elem ents (e.g. areas of sand and gravel; m an-m ade ground; site-investigation inform ation currently held in th e B G S natio nal the routes of m ajor highw ay projects). T he output consists of archive. T he records are checked for accuracy of location and height coloured m aps on paper and digital data that can be used for G IS w ith respect to sea level and geologically classified, and these applications. O ne oft he great advantages of these digital m aps is that enhanced data are encoded into digital form . they can be produced for irregular-shaped areas covering, for exam - pie, adm inistrative regions or route corridors that m ay include parts of one or m ore "standard" (rectilinear) m aps. Q uality assurance Q uality assurance (Q A ) checks are an integral part oft he databasing B o reh o le in fo rm a tion procedure, w hich currently follow s an intem al B G S quality assur- ance guide (com patible w ith the B ritish Standard 5750:1987). For exam ple, checks of the borehole grid coordinates e n s u re T he British Peological Survey holds more than 20,000 borehole that they correspond w ith the plotted position on the site m aps and records from the London region. M ost are of site investigation bore- w ith the site description. R eliability values of the raw borehole data holes drilled in the last 50 years to depths generally betw een 10 and are system atically entered into the database. D em onstrably unreli- 40 in ; several hundred, m any drilled in the last century, are of w ater able borehole records are not entered into the database. T he Q A w e lls into the C retaceo us C halk . A b ou t 20 of the boreho le s are m o re appraisal im poses reliability codings on five param eters relating to than 300 in deep and prove the pre-Perm ian basem ent (A llsop and th e b oreh o le rec ord : Sm ith, 1988). Sam ples from m any oft he borcholes proving the base- ．A ccuracy of grid coordinates m ent are curated in the B G S borehole-core collection. In addition, ．R eliability oft he borehole log com plete cores and/or representative sam ples from 19 boreholes ．A ccuracy of the O rdnance D atum proving the succession of Palaeogene strata are curated. Since there ．R eliability of the stratigraphical classification are few w ell-exposed perm anent sections in the region, these cores ．R eliability of the recorded depths in the borehole log are the reference sections for m any of the Palaeogene form ations and U sing the reliability factors, inform ation of a spe ci fi c quality are used to assist in interpreting borehole logs w here no m aterial is can be selected from the relational database. T he digital inform ation availab le for e xam inatio n is refined as com puter m odelling proceeds, and anom alous data are In order to assess the g e o logy of the L ondon region, four hori- reassessed and either corrected and re-entered or discarded. The pro- zons that can be easily recognised in borehole records (figure 2) have cess involves a num ber of iterations, dependent on the com plexity of been selected for entry into a database which contains the depths of the geological surface being m odelled, until a geologically satisfac- these horizons w ith respect to sea level. T his has enabled a synthesis tory result is achieved. of the vast quantity of data in the borehole records to be m ade, and the available inform ation to be reduced m anageable proportions. D ata processing The highest surface used is the base of m an-m ade grou n d , w hich includes the fill of pits, quarries and other excavations, and T he data are processed on the N atural Environm ent R esearch C oun- w aste deposits tipped onto form erly undisturbed ground. T he depth cil (N ER C ) V ax 8550 and 65 10 m ainfram e com puter cluster on the to base of these deposits in form er pits is highly irregular and hence B G S cam pus, using the follow ing softw are packages (figure 5): m eaningless and im practical to contour. The distribution of signifi- ．O R A C LE - a relational database m anagem ent system used to cant areas of m an-m ade ground and the thickness proved in bore- store, retrieve and m anipulate data (O racle, 1990); holes (show n as point data) are produced on them atic m aps, along ．G R A PH L O G - a B G S-developed p rogram (Flow er, 1987) used to w ith in form atio n ab o ut th e u se of the site . produce graphical borehole logs for easy reference purposes T he second surface is the base of th e su perficial deposits. In (available on-screen and as paper copy); L ondon these com prise the unconsolidated alluvial silts, clays and ．IS M (V ersion 7)- Interactive Surface M odelling: softw are peat of the m odem floodplain, and river-terrace sand and gravel designed and m arketed by D ynam ic G raphics (1990). It is used for deposits. T he alluvial deposits are too soft for foundations and the gridding, contouring, draw ing cross-sections and perspective depth to their base m ust be determ ined at all developm ent sites. The block diagram s. terrace deposits are a valuable aggregate resource, although m ost are R ecent develo p m ents in com puter processing have led to the exhausted or built over. T he terrace base is generally planar, data's being m odelled on stand-alone w orkstations. T w o soft w are although there are restricted overdeepened hollow s (scours), som e of packages are under trial, both run on Silicon G raphics Indigo 3000 w hich penetrate the base of the London C lay or even the top of the w o rk station s: C halk, filled w ith unconsolidated saturated sands, silts and gravels. ．EA R T H V ISIO N - w orkstation-based, and m arketed by D ynam ic T he third surface is the base of the London C lay. T he L ondon G raphics (1992). T his package com bines the facilities of ISM C lay underlies the drift deposits in m uch of London, and as it is w ith another D ynam ics G raphics product, Interactive V olum e strong and generally hom ogeneous, m ost of the larger buildings in M odelling (IV M ); central London are built on piles drilled through the superficial deposits into the L ondon C lay. The strata are usually w ell defined in borehole records, particularly as the underlying beds are contrasting F ig ure 5.- L O C U S P roject com p uter m odelling fl ow chart. soft sands, silts and clays of the W oolw ich, R eading, U pnor and Thanet Sand form ations. A s these underlying beds can be in S O F T W A R E hydraulic continuity w ith the underlying C halk, both their rapid lat- D IG 汀 八 L eral and vertical variation and also the w ater content pose problem s D A T A in tunnelling and foundations. H O L D IN G S

The low est surface, the to p o f the C retaceous C halk, is im por- H A R D W A R E tant as the C halk is a m ajor aquifer. It is essential therefore to be able to predict w here site investigation boreholes or any construction 霏 activity w ill encounter C halk in order to m inim ise the risk ot ground- 一PLOTTERS一 w ater pollution. 廊

Septem ber 1993 3 8 7

F igure 6.- Contours on the rockhead sur- face in p art of c entral L ondon. C ontours are a t 2 m in terva ls in m etres relative to O rdnance D atum (sea level). Stippled areas indicate L ondon C lay at outcrop.

levels w here the (geological) surface is k n ow n to b e ab se nt. B y com bining d a ta from geological m ap s and the borehole database, and by the use of appropriate com puter m odelling soft- w are, the data m ay be interrogated, m anipu- lated and corrected to produce geological m o dels co n sisten t w ith th e kn ow n surface geology. ，52苔 C om puter-generated geological data O ne example of a computer-generated con- tour plot, the base of the superficial deposits (rockhead), is show n on figure 6. Sim ilar plots are produced for each m odelled sur- face. Such com puter-generated surfaces can be displayed as perspective view s (fi gure 7) from any chosen vantage point (thus giving a 3-D appreciation of the structure), and cross-sections can be draw n along any line

S C O U R H (figure 8), show ing all the surfaces that are

- W 孟 m od elled . in su m m ary the database and softw are provides: rithm to calculate surface grids. For com pu- ．B orehole listings ． V U L C A N - E N V IS A G E - w o rk sta tio n - ．G raphical representation of borehole logs tational purposes, a surface is generated by based (V ulcan, 1992). (GRAPHLOG S) D ata are retrieved f r o m th e O R A C L E using the algorithm to calculate the height of the surface at a theoretically unlim ited num - ．D istribution plots of borehole sites d atab ase in to fi les suitab le for u se in th e m od- ．C ontour m odels ber of other points. In practice a grid w ith elling softw are. Four file types are used: scat- ．Isopachyte (thickness) plots of m ajor geo- tered data files for point inform ation; fault nodes at 10 m or 20 in spacing is used. These grids provide the basis for subsequent m od- logical units data files that contain digitised fault-plane ．C ross-sections and fence diagram s inform ation; polygon files that include, for elling and geological analysis. O ne of the ISM options u se d in this ．Perspective view s exam ple, areas of outcrop of a particular geo- ．B lock diagram s. logical form ation; and annotation files that w ork perm its the use of the full dataset in the contain digital topographical inform ation. grid calculation. T his m eans that in calculat- A lthough it is possible to com pute d i s- ing a particular surface, both borcholes that C o n clu sio n plays and perform various analytical tasks prove the surface and those that do not prove directly from scattered data, the m odelling it are used. This constrains the gridding and soft w are uses these data and a gridding algo- prevents the gridded surface rising above T he methodology for dealing with large volum es of geological data has been estab- lished for the L ondon region. Im plem enta- tion of digital m ap production and the ratio- nalisation of data, principally borehole data, has enabled routine production of com - ，20 puter-generated geological m odels of Lon- 翔 d on an d the m ean s to visu alise au tom ati- 、 cally a range of inform ation from point data 翔 to 3-13 m o de ls. 吸 T he geolo g i ca l understanding of the ground underlying urban areas that com es I ）cj 000 from geological surveying and the m odel- 1}} ling of borehole data is of particular use for:

F igure 7- E xam p le of a com puter-gen- erated persp ective view of t h e top of Chalk in central London (view ed户onz the north- east). D ep ths are in m etres. 1尽瓦。。

Episodes, v. 16, no. 3 W akeling, T R M , and Jennings, R A J, 1979, Engineering geology and the Tham es B arrier project, in O ele, E ed., Sym posium on engincering-geo- logical aspects of deltaic areas; Renesse, 1979, Proceedings: G 。二logic en M ijnbouw , v. 58,449-457. W hitaker, W , 1872, The geology of the London B asin, Part 1, M em oir: Lon- don, Geological Survey of England and W ales. W hitaker, W . 1889, Ile geology of London and part oft he Thames Valley, I奄are 8.- Example of computer-generatedg eological cross- M em oir: Geological Survey of England andW ales, 2 w .门 section in central London.

．Resource exploration and exploitation ．Construction and civil engineering R ichard E llison is a P rincipal G eol- ．Land-use planning ogist with more than 20 years' experi- ． H az ard asse ssm en t ence in the Land Survey of t he B ritish ．W aste disposal G eological Survey. H e is currently ．Pollution protection project m anagerfor the LO C U S p raj- 'R e sim ilarity of t h e basic geology of m any of the world's ect, producing digital geological maps conutbations (i.e. unconsolidated superficial deposits overlying bed- and 3-D m odels of London. H e has had rock that is m ore suitable than the cover for foundations and excava- responsibilityf or geological m apping tions) leads us to believe that the methods adopted for London could in a w ide variety of regions in the be applied elsewhere, to the benefit ofp lanning and developm ent. United Kingdom, including the W eald, the W orcestershire Basin, the P ennine B asin, the Craven Basin and E ast A ng- A cknow ledgem ents lia, and overseas in the Peruvian A lti- piano. H e is coauthor ofs everal Geo- logical Survey m em oirs, and has w rit- T hispaper is presented with the permission of the Director of the ten papers on top ics as diverse as British Geological Survey. Figures I to 4 were drafted by }& H ugh Q uaternary deposits in the English Crilly, Geological Survey of Northern Ireland. M idlands, Siluria”一刃evonian boun- dory strata, geologyfor planning, and fracture patterns in coal seam s. R eferen ces Steph en B ooth is a P rincipal G eologist A llsop,JM , and Sm hh,N J P, 1988. The deep geology ofE ssex: Proceedings with more than 20years'expenence in of the G eologists' A ssociation, v. 99, pp. 249-260. the Land Survey of the B ritish G eo- Berry, F G , 1979, Late Q uaternary scourh ollow s and related features in cen- tral London: Q uarterly Journal of Engineering G eology, v. 12, pp. 9-29- logical Survey. He is currently respon- British Standard 5750, 1987, Q uality System s, Part 1, Specification for siblef or databasing, computer model- design/developm ent, production, installation and servicing: London, ling and G IS f or the L O C U S project. British Standards Institution. In addition to a ssessing industrial m in- Brom ehead, C E N , 1925, The geology oft he country around N orth London, erals including Carboniferous coal, M em oir: London, G eological Survey ofG reat B ritain. Q uaternary sands andg ravels and Tri- Craig, R N , and Sim pson, B, 1990, potential problem s associated w ith rising assic evaporites, he has also under- groundw ater levels in the deep aquifer beneath London, Special Publics- taken geological m apping both in the tion: Tunnel Construction '90, Institution of M ining and M etallurgy, pp. United Kingdom , including Quatern- 1- 8 . D ew ey, H , Brom ehead, C E N , C hatw in, C P, and D ines, H G , 1924, The ary deposits in East Anglia, and over- seas in the Solom on Islands, W estern geology of the country w ound D anford, M em oir 271: London, G eologi- cal Survey of England and W ales. Pacifc, prospectingfor gold and cop- Dewey, H , and Brom ehead, C E N , 1925, The geology oft he country m ound per in Tertiary and Q uaternary island- South London, M em oir: London, G eological Survey of Great B ritain. a rc vo lca n ics. Dines, H 0 , and Edm unds, M A , 1925, The geology of the country around R om ford, M em oir 257: G eological Survey E ngland and W ales. Paul Strange is a Principal G eologist Driscoll, R , 1983, The influence of vegetation on the sw elling and shrinking in the B ritish G eological Survey. H e of clay soils in B ritain: (36otechnique, v. 33, pp. 93-105. joined the Survey in 1972, and has D ynarnic Graphics, 1990, ISM D ocum entation (Release 7): U SA , D ynam ic G raphics Inc. undertaken geological m apping in D ynamic Graphics, 1992, EarthV ision Docum entation (Release 1): U SA , England, Bolivia and the Solomon D ynam ic G raphics Inc Islands. In 1983 M r Strange w as see- Flower, S M , 1987, G R AP H LOG Docum entation: Edinburgh, N ERC [N at- onded to the H ong K ong governm ent ural Environm ent R esearch Council] Com puter Services. as a geotechnical engineer, special- G ibbard, P L, 1077, Pleistocene history of the V ale of St. A lbans: Philosoph- ising in urban geological m app ing. H e ical Transactions oft he R oyal Society of London, v. B 280, pp. 445-483. was head of the H ong K ong G eo- G ibband, P L, 1985, Pleistocene history of the M iddle Tham es V alley: C am - logical Survey betw een 1988 and bridge, C am bridge U niversity Press. 1991. B esides p roducing new geo- H utchinson, I N , 1980, Possible late Q uatem asy pingo rem nam s in central London: N ature, London, v. 284, pp. 253-255. logical m aps of the Territory, he lum N ickless, E F P, and Jackson, L 1993, D igital geological m ap production in w ritten a n um b er o f m em oirs a n d the U K- m ore than just a cartographic exercise: 16th International C ar- papers on the geology of H ong K ong. tographic Conference, C ologne, Proceedings. M r S trange now w orks w ith the O racle, 1990, OR AC LE d ocum entation: California, U SA , Oracle Corporation. LO CUS team, revising the geological V ULC AN , 1992. VU LCA N D ocum entation: A ustralia, KR JA Systems Inc. m aps of L ondon.

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