OR/16/004 Modelled datasets

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Barron, A J M. 2016. GSI3D model metadata report for HS2 Area 3 (Newton Purcell to Thorpe Mandeville). British Geological Survey Internal Report, OR/16/004.

All data is contained within this folder:

W:\Teams\GLE\GLETeamLeader\Data\HS2\HS2\GSI3D_Modelling_files\Area3, except for the GVS/GLEG (which is an overarching HS2 project file) which is located here: W:\Teams\GLE\GLETeamLeader\Data\HS2\HS2\GSI3D_Modelling_files.

GVS and GLEG files

The generalised vertical section (.GVS) and geological legend (.GLEG) files were assembled in a combination of Notepad, Wordpad and Excel and iterated as the model expanded and new units were encountered. A regional catch all approach was adopted from the very start. The GVS was created by S Thorpe using DiGMapGB-50 data. The GLEG files were also created by Steve Thorpe by clipping data from the BGS corporate DiGMapGB-10 and DiGMapGB-50 datasets along the route of the HS2 corridor, as defined by a 5 km buffer. Generic 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 HS2 GLEG file.

Borehole construction

S Thorpe 31/7/12: extracted Area 3 borehole subset from SOBI to W:\Teams\GLE\ GLETeamLeader\Data\HS2\HS2\ModelArea_3_MAB_JT\HS2_ModelArea3_Boreholes.xlsx.

A J M Barron 21/1/13-12/3/13: coding boreholes for Area 3 directly into the corporate BoGe data entry application and updating progress in above spread-sheet including (as per project guidance of S Thorpe 14/12/12), recording content code and coder (pre-existing and new), a rationale for inclusion/rejection, an indication of stratigraphical range proved, and an indication of whether to route a cross-section through. Bores were coded with bedrock units LEX from the project GVS, and RCS as appropriate to log lithology but from a preferred limited set (Table 2). ROCK may be used for ‘stone’ and UKNOWN where no lithology inferable. Where there were very dense clusters (including linear clusters) generally a subset of the deepest were examined and coded if required, with a view to a reasonable scatter and the likely layout of the sections, but in places the shallower logs were found to contain better detail. In the north-west around Middleton Cheney (SP44SE, SP54SW) there are a dense grid of bores for ironstone, into the Marlstone Rock Formation. Base of MRB was taken at the base of the lowest significant ironstone bed (>0.15 m) (also agreed with J Thompson who is coding Area 4 bores).

Table 2 Preferred RCS codes for lithology variants.
Formation Lex Log lithology or name Preferred RCS RCS translation
Northampton Sand Formation NS FLIR FERRUGINOUS LIMESTONE AND IRONSTONE
Marlstone Rock Formation MRB Mixed ferruginous lithologies FGLS FERRUGINOUS LIMESTONE AND FERRUGINOUS SANDSTONE
Marlstone Rock Formation MRB Ironstone FEST IRONSTONE
Marlstone Rock Formation MRB Beds of ironstone separated by clay MDFEST MUDSTONE AND IRONSTONE
Dyrham Formation DYS ‘Sandy clay’ etc. SAMDST MUDSTONE, SANDY
Dyrham Formation DYS Mixed siliciclastics MDSS MUDSTONE, SILTSTONE AND SANDSTONE
Dyrham Formation DYS ‘Middle Lias Clay’ — probably mudstone and siltstone MDST MUDSTONE
Dyrham Formation DYS Mixed siliciclastics, sandstone dominant SDSM SANDSTONE, SILTSTONE AND MUDSTONE
Dyrham Formation DYS SIMD SILTSTONE AND MUDSTONE, INTERBEDDED

Specific decisions about certain borehole logs are listed in Table 3.

Table 3 Boreholes used in the model on which decisions were made.
Borehole SOBI id Decision
SP53NE/165 Use log on p2
SP54SE/1 Used R J Wyatt log pp 1–2
SP53SE/3 Had to be hung from the DTM for EWrung_5
SP53NE/3 Had to be hung from the DTM for EWrung_8
SP54NW/23 Beyond a fault at end of NWSE_2: ignore
SP54NW?/331 Unclassifiable vs mapping
SP52NE/32 Log not trusted: ignore
SP62NW/32 Log not trusted: ignore
SP63SW/4 Site incorrect, thicknesses ok but ignore for correlation

S Thorpe 14th March 2013 — After boreholes coding was completed by Mark Barron (AJMB) the boreholes were extracted from the SOBI and BoGe databases by Steve Thorpe (ST) using a set of queries. The BLG needed to be de-duplicated and the Borehole Filter Tool was used to address this. The following priorities were applied to borehole records that were coded by more than one project. The records at the top of this list have a higher priority and the filter tool keeps these records and discards other matching records.

OR16004figa.jpg

This left a total of 337 boreholes coded (area3_bid_coded.bid) out of a total borehole count in Area 3 of 973 (Figure 3), generating the file Area3_BLG_coded_deduped.blg.

Figure 3 All boreholes in Area 3 set.
Coded boreholes over 10 m depth in green, under 10 m in black, uncoded boreholes in red.

The boreholes which AJMB identified as being useful for routing cross-sections through (total of 65) have also been generated as an additional BID file (area3_route_xs_through_bid.bid; Figure 4).

Digital Terrain Model

S Thorpe 18/3/13: 20 m DTM obtained from the BaldEarth model and trimmed to the project area (5 km buffer of the route shapefile).

Cross-sections

S Thorpe 18/3/13: Rung_16 and cross-sections running NW_SE were imported from Area 2. Buckingham 1:50 000 map cross-sections were imported from Area 2 with raster backdrops.

Geology and other shape files

S Thorpe 18/3/13: Bedrock, Superficial and AMG geological DiGMapGB-50 shapefiles loaded. No mass movement mapped within project area.

ST handed over to AJMB 14th Mar 2013 for review and subsequent changes in base data will be recorded in this section.

Other datasets

  • Mine plan data — none known or used
  • Seismic data — none used
  • Geophysical data — none used
  • Previous models used by this model — none used. The London Lithoframe 250 model (2007) models only the base of the Lias Group with a 1000 m mesh spacing — too coarse for the current purposes.
  • Chipping Norton memoir (Horton et al., 1987)[1] figure 15 (Lower Lias isopachyte map = CHAM), figure 19 (Middle Lias Silts and Clays isopachyte map = DYS) and figure 21 (Upper Lias isopachyte map = WHM) were scanned and georegistered.

Reference

  1. HORTON, A, POOLE, E G, WILLIAMS, B J, ILLING, V C, and HOBSON, G D. 1987. Geology of the country around Chipping Norton. Memoir of the British Geological Survey, Sheet 218 (England and Wales).