OR/15/044 Model workflow

Wakefield,O J W, and Barron, A J M. 2015. GSI3D Model metadata report for HS2 Area 6 (Cubbington to Hampton-in-Arden). British Geological Survey Internal Report, OR/15/044.

The standard GSI3D modelling workflow was followed for this project. GSI3D software utilises a range of data such as boreholes, digital terrain models (DTM) and geological linework to enable the geologist to construct a series of interlocking cross-sections. Borehole data is represented in GSI3D by two proprietary files: a borehole identification file (.bid), that contains ‘index’-level information including location and start-heights; a borehole log file (.blg), that contains the borehole interpretation. Constructing cross-sections is intuitive and flexible, combining borehole and outcrop data with the geologist’s experience to refine the interpretation.

Using both the information from the cross-sections and the distribution of each unit a calculation algorithm creates the triangulated surfaces for the top and base of each unit. In order to control the relative vertical ordering of the calculation, a generalised vertical section file (.gvs) is established. A proprietary legend file (.gleg) is created to control symbolisation of the cross-section and model. The modeller can view all the units in 3D and iteratively return to the cross-section to make amendments or add further cross-sections to refine the model. This process is a standard methodology within BGS for modelling Quaternary and simple bedrock horizons and is fully documented in Kessler et al (2009).

Ten additional helper sections (Figure 7) were created in specific problem areas. To aid the calculation of bedrock units in faulted areas, scattered data points were created for the geological units that intersect the base of the model. This was then manipulated in GSI3D so that it could be applied to the respective geological units. This process aided the calculation of the geological units to the basal model limit (-30 m O.D).