It is gratifying to the author that his paper has stimulated such interest, and he wishes to thank the discussers for their contributions.
In reply to Professor Hutchinson, it is agreed that the summary plot of residual strength data presented as Fig. 10 of the original paper was not a complete ‘state-of-the-art’ picture, although, in retrospect, the phrasing of the summary would tend to suggest that it should have been. This (apparent) claim is a relic of the first draft of the paper, which as it evolved, had to be made shorter, and material not central to the case shear, is accepted. In the context of the original paper, however , the phrasing is correct, since the ‘blue’ London clay is generally so much more deeply buried than the ‘brown’, and is subject to much higher levels of effective stress.
Dunbaven describes an interesting experiment. However, the author would like to point out that the ‘weak layer’ in the Herne Bay case is not the Oldhaven Beds, but a basal layer in the London Clay. Failure was in every case confined to the London Clay. This need not alter the general conclusions of the discusser, of course.
At Herne Bay, the underlying Oldhaven Beds are stronger than the London Clay, and the shape of the field failure surfaces appear to be controlled to a large extent by the depth of the Oldhaven Beds/London Clay interface below sea level. It would be extremely interesting to see whether this effect could be
- © The Geological Society, London 1980