The 3D geology of London and the Thames Gateway.docx

The 3D geology of London and the Thames Gateway: a modernapproach to geological surveying and its relevance in the urbanenvironmentABSTRACTAs a provider of geological advice to industry, academia and the public, the British Geological Survey (BGS) has recognized the need to change the way it presents geoscientific information, resulting in the construction of attributed 3D geological models. The need to deliver 3D modelling solutions is of great importance in urban areas, where geological factors play a major role in supporting ground investigations and sustainable water management studies. The 3D geological model of London and the Thames Gateway occupies an area of approximately 3200 km2 and extends to a depth of 150 m. It includes a total of 38 units, ranging from Artificial Deposits and Quaternary sediments down to Tertiary and Cretaceous bedrock. The model is built using existing geological surveys, DEMs and extensive borehole and site investigation data. Modelling was carried out using GSI3D (Geological Surveying and Investigation in 3 Dimensions) software. This software and its associated workflow produce a series of gridded volumes of the geological units, constrained at depth by a network of cross-sections constructed by the geologist. The Thames Gateway model was attributed by assigning property values to each geological unit. This has provided a way of visualizing the spatial relationships between geological units with differing properties. The model has revealed previously unrecognized geological information. Further benefits of the attributed model include the ability to visualize and appreciate the link between lithology and physical characteristics. Such models will produce the decision support system necessary for the sustainable development and management of todays megacities.作為向工業(yè)、科學(xué)界和公眾提供地質(zhì)方面建議的機(jī)構(gòu)，英國地調(diào)局意識到要改變它提供地質(zhì)科學(xué)信息的方式，需要建立屬性化的3D地質(zhì)模型。實(shí)現(xiàn)3D地質(zhì)模型解決方案的需求在城市地區(qū)是非常重要的，城市地區(qū)地質(zhì)因素在支持地表調(diào)查和可持續(xù)水資源管理發(fā)揮重要的作用。倫敦3D地質(zhì)模型和泰晤士門戶占據(jù)一個(gè)大約3200km2和大約150m深的區(qū)域。包括總共38個(gè)單元從地表沉積和第四紀(jì)沉積向下到第三紀(jì)、白堊紀(jì)基巖。建立模型使用了現(xiàn)有地質(zhì)調(diào)查手段、數(shù)字高程模型、大量鉆孔數(shù)據(jù)、工程勘測數(shù)據(jù)。這個(gè)模型使用GSI3D軟件實(shí)施。這個(gè)軟件和其相關(guān)的工作流程產(chǎn)生了一系列地質(zhì)單元的網(wǎng)格體積，在一定深度由地質(zhì)學(xué)家建立的網(wǎng)狀橫截面所控制。泰晤士門戶模型是給每個(gè)地質(zhì)單元分配屬性值，這為使得不同屬性值的不同地質(zhì)單元之間的空間關(guān)系可視化提供了一種途徑。這種模型表示出了之前沒有識別出的地質(zhì)信息。這種模型更多的優(yōu)勢包括可視化的能力和鑒別巖石學(xué)和巖石物理性質(zhì)的聯(lián)系。這種模型會(huì)提供一個(gè)今后特大城市可持續(xù)發(fā)展和管理所必需的決策支撐系統(tǒng)。1 INTRODUCTION 簡介Greater London is the biggest Megacity in the European Union, with a population approaching 14 million. Urban development in the region continues apace, with current regeneration and infrastructure programmes including new rail links, bridges, sewers, the creation of the Thames Gateway Development Area downriver from the city and the construction of the 2012 Olympic site. Since the 19th century, when London underwent rapid expansion, building and infrastructure projects have contributed key information about the geology beneath the city. Building on this accumulated knowledge, geological advice underpins modern construction and engineering projects, and draws attention to potential hazards and impacts in particular with regard to surface and groundwater. Technological advances in the digital age now enable the existing data to be portrayed not only as 2D maps, often only interpretable by geologists, but as attributed 3D models that clearly show rock-relationships to nongeologists. BGS has recently completed the first set of detailed 3D geological models of the shallow subsurface for London and the Thames Gateway.倫敦是歐盟成員中最大的城市，人口達(dá)到1400百萬。隨著現(xiàn)代的規(guī)劃和包括新的鐵路聯(lián)絡(luò)線、下水管道、橋梁和從城市延泰晤士河下游的泰晤士門戶發(fā)展地區(qū)的建設(shè)及2012年倫敦奧運(yùn)會(huì)選址的建設(shè)等一批基礎(chǔ)設(shè)施項(xiàng)目，城市的發(fā)展在這一地區(qū)繼續(xù)快速進(jìn)行。自從19世紀(jì)，當(dāng)倫敦經(jīng)歷了快速的擴(kuò)張，高樓建筑物和基礎(chǔ)設(shè)施工程為城市之下的地質(zhì)提供了關(guān)鍵信息?；谶@些知識的積累，地質(zhì)方面的建議加固了現(xiàn)代城市建設(shè)和工程項(xiàng)目的基礎(chǔ)，特別的并對有關(guān)地表和地下水的影響和潛在危害引起了足夠的重視。數(shù)字技術(shù)的進(jìn)步使得現(xiàn)有的數(shù)據(jù)不僅可以被描繪成為2維的地圖（通常只有地質(zhì)學(xué)家能解釋），還可以描繪成為3維的、能給非地質(zhì)學(xué)家清晰顯示出巖石關(guān)系的模型。英國地質(zhì)調(diào)查局最近完成了第一版?zhèn)惗睾吞┪钍块T戶淺表層3維地質(zhì)模型。2 THE GEOLOGY OF THE LONDON AREA倫敦地質(zhì)概況The bedrock geology of the London area covered by the 3D models is part of the London Basin, a NESW trending syncline (Figure 1) (Ellison et al.,2004). The London Basin formed in Oligocene to mid-Miocene times, during the main Alpine compressional event that affected southeastern England. The oldest bedrock unit, the Cretaceous Chalk Group, crops out forming a rim around the Basin. The Chalk, which is over 200 m thick, is the regions principal aquifer, famous historically for its artesian flow from wells sunk near the center of the Basin and its susceptibility to collapse due to dissolution. Overlying the Chalk, the oldest Paleocene deposit is the Thanet Sand Formation. This Formation consists of a sequence of fine-grained glauconitic sands with a basal bed of flint cobbles and boulders derived from the Chalk. The Thanet Sand reaches a maximum thickness of around 40 m in the east of the area but thins rapidly westwards to its limit beneath western London. Above the Thanet Sand lies the Lambeth Group. This lithologically variable group is up to 30 m thick in the area, consisting of variable proportions of sands, silts, clays and gravels. It is characterised by its spectacular colour-mottled clays which were prized for brickmaking. The overlying Eocene sediments form the Thames Group, which consist of the basal Harwich and an upper London Clay formations. The Harwich Formation consists predominantly of sand and pebble beds up to 10 m thick. The London Clay Formation comprises up to 150 m of grey to bluegrey, bioturbated, silty clay. Higher Eocene sediments of the sandy Bagshot Formation occur as isolated outliers on some of the highest hills in the area, reaching a thickness of around 30 m. Superficial Quaternary deposits are widely developed in the London area. These deposits include river and intertidal alluvium, peat, brickearth and river terrace deposits associated with the current and previous courses of the River Thames. Urban development and industrial mineral extraction in the region have resulted in a complex distribution of worked, made and infilled ground, collectively referred to as Artificial Deposits. 倫敦地區(qū)三維模型覆蓋區(qū)域基巖地質(zhì)是倫敦盆地的一部分，一個(gè)北東南西傾向的向斜。倫敦盆地是在奧陶紀(jì)到中中新世一個(gè)影響英國東南的主要阿爾卑斯擠壓事件時(shí)期形成。最古老的單元白堊紀(jì)白堊組沿著盆地出露形成邊緣。超過200m厚的白堊組是區(qū)域重要的含水層，歷史上因其靠近盆地中心從泉水中承壓水流下滲和由于溶解而易遭受塌陷而聞名。 白堊組上面最古老的古新世沉積是薩尼特砂巖組。由一系列細(xì)粒海綠石和基底燧石鵝卵石組成。薩尼特組砂巖最大厚度在東部區(qū)域大約40m，但是快速向西變薄，在倫敦西部底部達(dá)到極限。這一巖性變化多樣的組合區(qū)域上達(dá)到30m厚，由多種成分砂、粘土、淤泥和礫石組成。以特殊的顏色斑為特征，曾經(jīng)適合制磚。始新世上部的沉積物形成泰晤士組，由基底哈里奇組和上部的組成。哈里奇組主要由砂和卵石底組成厚達(dá)10m。倫敦克萊組主要由灰到藍(lán)灰色、生物擾動(dòng)成因的、淤泥質(zhì)粘土組成，厚達(dá)150m。表面第四紀(jì)沉積在倫敦地區(qū)廣泛分布。這些沉積包括河流和潮間帶的沖積物、泥炭、制磚粘土和河流階地沉積物。城市發(fā)展和工業(yè)采礦造成了勞動(dòng)力、制造業(yè)和密集型團(tuán)體的復(fù)雜分布。The principal engineering geology and environmental factors associated with the geology of the London area are presented in Table 1.3 PREVIOUS SURVEY WORKThe history of geological surveying in the London area began with publication of the first memoir in 1872 (Whitaker, 1872), based on mapping that began in 1861. 倫敦地區(qū)地質(zhì)調(diào)查歷史開始于1872惠特克第一版回憶錄的出版。Early survey work recognized the role of geology in underpinning rapid urban expansion of Victorian London (Culshaw, 2004; Culshaw et al. 2008).早期的地質(zhì)調(diào)查工作認(rèn)為地質(zhì)工作是支撐倫敦維多利亞快速擴(kuò)張的角色。These early survey publications contain numerous sections from rail cuttings and accounts of borings and tunnels that illustrate the subsurface geology of the area. Continued urban growth, including the construction of the London Underground (metro), road and further rail networks demanded up-to-date geological information, and provided the data to support several revised maps, accounts and more recently, 3D modelling work (Strange et al., 1998). 隨著城市的發(fā)展，包括倫敦地鐵、道路和鐵路網(wǎng)的建設(shè)需要及時(shí)更新的地質(zhì)信息，并提供數(shù)據(jù)支持修改地圖、報(bào)告，最近是三維建模工作。The current memoir of the London area (Ellison et al., 2004) describes the 4 mapsheets published in the 1990s for the North London, South London, Romford and Dartford districts. 最新的關(guān)于倫敦地區(qū)的論文敘述了4個(gè)1990年出版的南北倫敦的圖幅。This work provides an increased level of information on the subsurface geology through a range of subcrop maps, structure contour plots and 3D views. Recent advances in affordable computing power, digital data and software development have allowed geologists to take the next step in understanding and communicating the subsurface geology of the London area: not just as maps but through the construction of detailed 3D geological models.4 THE MODELLING APPROACHThe BGSs approach to 3D geological modelling of relatively shallow and un-deformed strata, including that of the London area, is described by Kessler and Mathers (2004) and Kessler et al. (in press). 英國地調(diào)局相對淺的和未變形地層包括倫敦地區(qū)的三維地質(zhì)建模方法由K和M提出。This methodology has been successfully employed in a range of research in the UK and overseas (Merritt et al., 2007; Wycisk et al., in press). 這種方法已經(jīng)成功地在英國和海外一系列研究中實(shí)施。The GSI3D method utilises a digital terrain model, geological surface linework and downhole borehole data to enable the geologist to construct regularly spaced, intersecting cross sections. 三維地質(zhì)建模方法利用數(shù)字地體模型、地表拉線盒向下鉆孔數(shù)據(jù)使得地質(zhì)學(xué)家建立有規(guī)律的、空間性的、交叉橫切面的部分。These are combined in a fence diagram which shows the correlation of individual lithostratigraphic units and their lateral extent in the subsurface.這些組成在一個(gè)柵狀剖面圖內(nèi)，剖面圖內(nèi)能顯示各巖石地層單元和它們在地表下橫向伸展之間的關(guān)系。Mathematical interpolation between nodes that define the base of each unit produces a solid model comprised of a series of stacked triangulated objects corresponding to each of the geological units present (Figure 2).節(jié)點(diǎn)之間進(jìn)行數(shù)學(xué)插值定義了每個(gè)地質(zhì)單元的基準(zhǔn)，產(chǎn)生了一個(gè)固體模型，由一系列代表每個(gè)地質(zhì)單元的堆積三角形對象組成。Geologists interpret their sections based partly on factual information, where the borehole information and correlation is secure, and partly on geological experience- the shape looks right. This looks right element pulls on the modellers wealth of understanding of geological processes and knowledge gathered over a career in geology. The process of 3D modelling allows the geological surveyor to collate and consider a far wider range and volume of data than with conventional 2D map construction. Surface and subsurface information can be brought together and visualised from any perspective. This contextually-enhanced view of the data highlights spatial relationships and improves the accuracy of the geological interpretation.5 MODELLING IN THE LONDON AREAModelling in the London area has been completed for a variety of strategic, scientific and commissioned projects, each fit for purpose at a range of scales. 倫敦地區(qū)地質(zhì)建模已經(jīng)完成大量的戰(zhàn)略的科學(xué)的和委托的任務(wù)，每項(xiàng)都在指明的范圍之內(nèi)。The Thames Gateway model (Figure 1) is built from over 4000 boreholes and over 2,300 line-kilometres of north-south and east-west trending cross-sections. 泰晤士門戶模型The model includes a detailed subdivision of artificial ground, Holocene deposits and selected Bedrock units. 這個(gè)模型包括一個(gè)詳細(xì)的假想地面的分支、全新世礦床和部分基巖單元。The Thames Gateway model is commensurate with geological mapping at a scale of 1:10000. 泰晤士門戶模型和1:1萬地質(zhì)填圖相當(dāng)。A second modelling initiative, the London LithoFrame, extends model coverage of the London area to include Outer London, southwest Essex and northwest Kent (Figure 1). 第二個(gè)創(chuàng)新的建模，倫敦3D地質(zhì)框架，伸展覆蓋了整個(gè)倫敦地區(qū)和倫敦外部，艾克塞斯西南河肯特西北。This strategic model is based on over 6,700 line-kilometres of correlated cross-sections. 這個(gè)戰(zhàn)略模型以超過6700km的相互關(guān)聯(lián)的橫截面為基礎(chǔ)。This model provides an equivalent level of detail to 1:50 000 scale mapping and represents the 3D equivalent of the geological map of London (Figure 3). 這個(gè)模型提供相當(dāng)于1:1.5萬地質(zhì)填圖和代表相當(dāng)于三維倫敦地質(zhì)圖的水平。The Thames Gateway and London LithoFrame models occupy an area of approximately 3200 km2. 泰晤士門戶和3D建模占據(jù)了相當(dāng)于3200km2的區(qū)域。The combined model extends to a depth of 150 m, and represents a total of 38 units.聯(lián)合模型向下延伸深度達(dá)到150m，代表總共38個(gè)單元。In many parts of the model, borehole data is available in such large quantities that not all records can be used.模型的許多部分中，鉆孔數(shù)據(jù)大部分是可以獲得的但是不是所有的都能使用。A review and prioritisation of the available data ensures that the most reliable and representative records are incorporated in the model. Boreholes that are not considered initially can be introduced at a later stage to refine the interpretation. Further modelling at smaller and larger scale has been completed. These models provide additional information on the deeper structure of the London Basin, and very high levels of detail at specific sites (Royse et al., 2006a). All 3D models in the London area are constructed to integrate seamlessly across scales.6 LONDON MODELS EXPLOREDGSI3D provides a suite of investigative tools and visualisation modes that allow calculated models to be explored in response to a range of geology related queries. GSI3D提供一套調(diào)查性質(zhì)的工具和可視化模式可以使計(jì)算模型針對許多地質(zhì)相關(guān)的問題能夠勘查到。These tools allow the geological framework and underlying data to be investigated in ways that would be impossible, or require significantly greater effort, to achieve through manual 2D mapping and GIS technology alone. 這些工具可以使地質(zhì)建模格架和基礎(chǔ)數(shù)據(jù)被調(diào)查變成不可能，或者需要更大的努力通過手繪二維填圖和GIS技術(shù)單獨(dú)完成。The spatial definition of surface and concealed extents for each geological unit provides an immediate benefit over conventional 2D mapping that typically represent only the outcrop distribution of each unit. 表面和每一個(gè)地質(zhì)單元隱藏的部分的空間定義提供了一個(gè)比通常情況僅僅能表示每個(gè)地質(zhì)單元露頭分布的傳統(tǒng)二維地質(zhì)填圖直接的好處。The surface and concealed extent of each unit are presented in both 2D and 3D, allowing the spatial relationship between multiple concealed units to be considered. 每個(gè)地質(zhì)單元表面和隱藏的部分都能用二維和三維表示出，使得多個(gè)隱藏的地質(zhì)單元的空間關(guān)系能夠被考慮。Surfaces defining the tops or bases of units can be readily investigated through contouring, colourgraded shading and 3D visualisation.每個(gè)地質(zhì)單元頂部或基底表面定義可以很容易的通過圈定、色彩分級和三維可視化來調(diào)查。Similarly, unit thickness can be explored to reveal further detail on the morphology of each unit. 同樣的，地質(zhì)單元的厚度可以通過勘查來反映每個(gè)地質(zhì)單元形態(tài)學(xué)更多的細(xì)節(jié)。In the London area, this approach has resulted in an improved rockhead elevation model and a far greater understanding of the distribution and extent of River Thames Terrace Deposits, and their denudation chronology.在倫敦地區(qū)，這種方法成功實(shí)現(xiàn)了改進(jìn)基巖頂抬升模型、泰晤士河階地沉積分布范圍的更深的理解和他們的剝蝕年代。3D modelling of these deposits has revealed scour hollows and their relationship to underlying units. 這些沉積三維模型顯示了沖刷洞和他們與下面地質(zhì)單元的關(guān)系。The geological succession at any point on the model can be visualised using the borehole prognosis tool and reported as a “synthetic log”. 地質(zhì)序列在模型上任何時(shí)候可以通過鉆井預(yù)測工具進(jìn)行可視化而且被報(bào)告為合成測井曲線。The model can be sectioned in any orientation to provide vertical profiles or horizontal profiles (Figure 4). 這個(gè)模型在任何方向可以被切成橫斷面來提供垂直或水平的輪廓。In the London area, “synthetic sections” have been constructed along proposed linear routes to support a range of engineering projects. Model visualisation in the BGSs walk-in 3D projection room has encouraged collaborative working and knowledge transfer between groups of geologists. This has resulted in the development of a revised structural framework for the London area: the active stereo capability of the facility has highlighted geometric features in the modelled bedrock surfaces that, together with information from outcrop, can be confidently interpreted as a network of previously unrecognised faulting and folding (Figure 5). This improved structural model will inform the sustainable management of groundwater resources in the area. Modelling in the London area has highlighted improvements to the published geological map, including modification of the structural relationship, spatial extent, and lithostratigraphic classification of units. Changes specified by the model will feed back to the 2D geological map (DigMapGB) ensuring consistency between 2D and 3D data. Advanced exploration of the London modelling is facilitated by close integration of GSI3D outputs with 2D and 3D GIS applications, 3D modelling applications and hydrogeological software including Zoom and ModFlow (Kessler et al., 2007).7 EXTENDED MODEL ATTRIBUTIONThe lithostratigraphic model provides a framework into which additional qualitative physical property based information for each modelled unit can be placed, analyzed and reported. 巖石地層模型提供了一個(gè)框架，每一個(gè)模型化的地質(zhì)單元的額外的基于定性物理屬性信息在這個(gè)框架里得以放置、分析和記錄。The integration of property-based information allows multiple thematic representations of the model to be derived, each addressing specific engineering geology or environmental applications. 基于屬性的信息整合使得模型多種專題表達(dá)能夠被導(dǎo)出，每種能解決特定的工程地質(zhì)或環(huán)境應(yīng)用。The investigative tools available to explore the geological framework can be applied to the thematic representations of the model, providing a powerful mechanism for knowledge transfer. 能應(yīng)用的調(diào)查工具來研究地質(zhì)框架可以被應(yīng)用到模型專題表達(dá)，提供一種強(qiáng)大的知識轉(zhuǎn)換機(jī)制。Bulk attribution of the Thames Gateway model with hydrogeological, engineering and confidence data obtained from over 3200 boreholes, trial pits and geophysical investigations, has provided a decision support tool for a range of end-uses including the tunnelling and construction industry, water authority and developers of ground source heat pumps (Royse et al., 2008 and Royse et al., in press). Model attribution with engineering properties,