DISCUSSIONS

Anisotropic consolidation of Leda Clay: Discussion

R. J. MITCHELL AND C. B. CRAWFORD Division of Building Research, National Research Council of Canada, Ottawa, Canada

Received October 7, 1969

Accepted for publication October 14, 1969

Walker and Raymond (1969) discuss a factor that may have considerable influence on the consolidation of soft clays under field load- ings: the variation of shearing stresses through- out the soil mass. Their experimental results on Leda Clay show only a small increase in compression index due to an increase in de- viatoric stress (Fig. 2 of the paper) indicating that this material may not exhibit a state boundary surface (or yield surfaces) of the shape implied by the idealization presented in Fig. 1 of the paper. The effect of increased deviatoric stress on the rate of pore pressure dissipation (Fig. 4 of the paper), however, ap- pears to be of major significance but is a result isolated from the theoretical considerations ~resented. The writers find the data and dis- I

cussion presented in the paper both informa- tive and interesting, but would like to make the following points with regard to the interpre- tation of the results:

In an oedometer test the condition of no lateral strain requires that the dilatancy d v / d ~ = 1 S. If this value is used in conjunction with stress-dilatancy relations presented in Fig.

8 of the paper it might be inferred that 7 varies. from a value greater than unity to about 0.75 as p increases from 0.6 kg/cmVo 4 kg/cm2. Since KO = u ' ~ / u ' ~ = (3 - 7) / (3 + 27) the stress-dilatancy relations appear to predict that KO would increase roughly from 0.3 to 0.5 over the same range of mean normal stress. Do the authors support this interpretation? It would seem that KO should decrease with increased pressure for a lightly overconsolidated soil.

The writers do not agree with the conclusion, drawn by the authors with reference to Fig. 9, that "the plastic strain-increment ratio was shown to be a unique function of effective stress ratio." The irrecoverable deformations during the undrained phase of the tests are not con- sidered and the possible effect of stress path has not been investigated. The experimental data in Fig. 9 appear to represent a particular flow relation during secondary compression and may be useful in predicting secondary deforma- tions in situ.

WALKER, L. K. and RAYMOND, G. P. 1969. Aniso- tropic consolidation of Leda Clay. Can. Geotech. J . 6, pp. 271-286.

Canadian Geotechnical Journal, 7, 92 (1970)

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