OR/15/044 Model datasets

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.

GVS and GLEG files

The generalised vertical section (.gvs) and geological legend (.gleg) files were assembled using Notepad or Excel and iterated as the model expanded and new units were encountered. The GVS was based on DiGMapGB-50 data by identifying all those geological units that are within a 5 km area of the HS2 route. However some units occur only in subcrop, so additional units in the GVS had to be appended as modelling progressed. The GLEG files were created using the standard BGS colours from DigMap-50. Overall GVS and GLEG files were created for the whole HS2 route, rather than for each individual model area. Thus the units used in this model are only a subset of those available in the overall HS2 GVS file.

Geological linework

Figure 2 and Figure 4 show the 1:50 000 scale mapped bedrock geology and superficial cover respectively. This, and the artificially modified ground data (Made Ground etc.), is generalised from the survey-scale 1:10 000 scale data. Lenticular beds were modelled by constructing projected boundaries to separate upper and lower units where a lenticular unit is absent, e.g. the Wolston Sand and Gravel Member within the Wolston Clay. Additional LEX-RCS codes were required (e.g. GLLMP1-XCZ, GFDMP0-XSV, WOC1-XCZ; Figure 7) in order to allow instances of the otherwise same superficial LEX-RCS code to be used at more than one stratigraphical level.

Digital terrain model

The terrain model used in this model was the BGS Bald Earth 20 m DTM obtained from the BaldEarth model and trimmed to the project area (5 km buffer of the route shapefile). A NextMap DTM was also included, but not used for modelling.

Borehole data

The distribution of borehole logs held in the BGS Single Onshore Borehole Index (SOBI) is generally concentrated in the central eastern section of the model (around southwest Coventry) and poor elsewhere (Figure 9). However, elsewhere some useful deeper boreholes are available, originally drilled for the Warwickshire Coalfield.

Figure 9 SOBI borehole distribution for HS2 Area 6. Boreholes are coloured according to their drilled depth. Green boreholes have drilled depths of 0–10 m, blue are 10–30 m and red are over 30 m. Black boreholes have unknown drilled depths.

A review of borehole records in the BGS Single Onshore Borehole Index (SOBI) in the model area was carried out and those that held sufficient geological information were selected for coding in the BGS Borehole Geology database (BoGe). After borehole coding was completed, the boreholes were extracted from the BGS Single Onshore Borehole Index (SOBI) database for use in the 3D modelling software using a set of queries. The borehole log file (.blg) needed to be deduplicated and a borehole filter tool was used to address this. A set of priorities were applied to borehole records that were coded by more than one project.

Some borehole records included now redundant stratigraphy, notably the use of the Keele Formation, now named Alveley Member (ALY), part of the Salop Formation (Waters et al., 2009), but in all cases, current stratigraphy was coded in the Borehole Geology database.

Other datasets

• Cross sections from BGS 1:50 000-scale maps