3D Geological Models – A robust platform to build upon

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 In recent years BIM has focused on the built aspects of construction, however the ground conditions are arguably equally if not more important. Unexpected ground conditions are the most common cause of site delays and can result in significant financial costs. This can be attributed to substandard approaches to site investigation and limited availability of high quality geotechnical data and subsequent interpretation. Opportunities to improve ground modelling and the sharing of geological and geotechnical data should therefore be of great benefit to the industry.

The British Geological Survey (BGS) have been collecting and managing borehole and site investigation data for nearly two centuries and this data is largely available free of charge online via the Geology of Britain Viewer as well as Web Map Services  (WMS) Internally this data has traditionally been used to compile national geological map data as well as the systematic study of the properties of the rocks and soils that make up the subsurface of the UK. However over the past 15 years the focus has increasingly shifted to 3D geological modelling.

Similar to the evolution of BIM, the digitisation of most of BGS archives combined with the availability of increasingly powerful computers, graphic cards and software systems have led to a complete transformation of the working practices and outputs of the BGS, culminating in the inception of the National Geological Model . This model is based on the geological interpretation of all available data and knowledge at the time. It is built from a series of interconnected geological cross sections based on borehole information and geophysical investigations and from geological maps and interpolated geological surfaces. However, the geological understanding of an area can change and new data in the form of boreholes or exposures of rocks in cuttings will become available over time. It is therefore crucial that this model is not a static publication but that it can evolve with increasing external input.

Apart from the national scale National Fence Diagram, BGS holds many detailed geological models of major conurbations such as London, Manchester and Glasgow, but also regional models of many rural areas. BGS continually improves model coverage and can develop models for bespoke requirements.

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These models are available in view format via the Groundhog web portal which allows users to obtain model-derived geological cross sections and surfaces – an example section report is shown in Figure 3. These cross-section images might be useful as a static output inside a report, whilst geological surfaces can be requested under license for inclusion in BIM software. Whilst being able to view such data is a big step forward compared to the 2D geological map, being able to truly interrogate and work with the geological data and models is the ultimate goal.

The real challenge is now to deliver the geological data and models in an integrated fashion directly into the systems and workflows of consultants and engineers, hence

fulfilling BIM level 2 requirements. BGS is preparing itself for the increasing availability of external digitally captured geological data and models, positioning itself at the heart of an increasingly collaborative community ensuring the data and observations generated today will still be available in the future.

Case study:

Recently BGS undertook a 3D modelling project along 28 km of railway line between Leeds and York on behalf of Tata Steel Projects (Burke et al 2015). The final 3D geological model indicated the top and base elevations of the geological units. The base of the weathered rockhead and the location of major faults were defined as separate surfaces. The purpose of the work was to identify areas where targeted ground investigation could be undertaken and an early assessment could then be made on whether to design deep or shallow mast foundations which are required for the electrification of the route. The model was delivered as CAD files and the client was able to integrate the Conceptual Ground Model (CGM) within their in house BIM workflow.

References:

Burke, H.F.; Hughes, L.; Wakefield, O.J.W.; Entwisle, D.C.; Waters, C.N.; Myers, A.; Thorpe, S.; Terrington, R.;Kessler, H.; Horabin, C.. 2015 A 3D geological model for B90745 North Trans Pennine Electrification East between Leeds and York. Nottingham, UK, British Geological Survey, 28pp. http://nora.nerc.ac.uk/509777/

Mathers, S.J.; Terrington, R.L.; Waters, C.N.; Leslie, A.G.. 2014 GB3D : a framework for the bedrock geology of Great Britain. Geoscience Data Journal, 1 (1). 30-42. http://nora.nerc.ac.uk/505851/

Mathers, S.J.; Burke, H.F.; Terrington, R.L.; Thorpe, S.; Dearden, R.A.; Williamson, J.P.; Ford, J.R.. 2014b A geological model of London and the Thames Valley, southeast England. Proceedings of the Geologists’ Association, 125 (4). 373-382.10.1016/j.pgeola.2014.09.001

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