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Commentary |
Sir William Halcrow & Partners, 3 Shortlands, London W6 8BT.
The author is to be congratulated on a most interesting paper, but with regard to the use of the computerized data bank of borehole records for the Jubilee Line investigation it should be emphasized that the data bank was not programmed to include such detail as the presence of hard limestone bands, flint beds and minor lithological variations along the route. This detail was added from existing borehole information.
Furthermore, since the computer was not programmed to include a break and known throw across faulted areas, faults were represented by steep monoclinal gradients between definitive boreholes. For example, Fig. 1, which is based on approximately 2500 boreholes covering the London area, shows the Raynes Park and Greenwich faults south of the Thames river as monoclinal flexures superimposed on the general geology.
Some of the differences between the real and predicted geologies for the Jubilee Line can be explained by lack of previous borehole data along certain sections of the route and this was taken into account in the siting of the investigation boreholes.
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