OR/16/034 Model datasets
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
All Area 9 cross sections are located within BGS 1:50 000 Sheet 168 (Birmingham), surveyed between 1978 and 1992, published in 1996 and accompanied by a memoir (Powell et al., 2000[1]). The cross-sections use DiGMap 1:50 000 scale geological map data.
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
Borehole records examined included both Keyworth and Wallingford held logs. Closely clustered sets of boreholes were not all coded but the deepest and most representative were included. Any significant local variation in sequence was also recorded by coding. Entries were all made directly into the corporate BGS Borehole Geology database (BoGe). However, many of the boreholes were either very shallow and thus did not provide any data on the bedrock geology, or did not contain sufficient information to be coded in any meaningful way.
After borehole coding was completed, the boreholes were extracted from the BGS Single Onshore Borehole Index (SOBI) database 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. Figure 7 shows the distribution of the 105 boreholes used to constrain the Area 9 cross-sections that inform the route section.
Borehole locations are shows as blue dots; black line is the HS2 Birmingham Spur route section; red lines are cross-sections constructed to inform the route section. Contains Ordnance Survey data © Crown Copyright and database rights 2016.
Raster images
Information from BGS Birmingham memoir (Powell et al., 2000[1]), including comments about rock types and unit thicknesses was used to inform the cross-section construction. Memoir figures 20a and 20c (Contour map for the base of the Bromsgrove Sandstone Formation, and for the base of the Mercia Mudstone Group, respectively, covering the west and centre of the Spur) and 27 (Rockhead contours for part of central Birmingham) were georegistered and added to the project (see below).