Triaxial tests were performed on undisturbed samples from the same depth of organic clay w...

Triaxial tests were performed on undisturbed samples from the same depth of organic clay whose preconsol idation load, determined from consolidation tests, was in the range 90 to 160 kPa. The principal stresses at failure of two CD tests were

Test No. 1: σ3 = 200 kPa, σ1 = 704 kPa

Test No. 2; σ3 = 278 kPa, σ1 = 979 kPa

Data from one CD test on the same clay are shown below. The effective consolidation pressure was 330 kPa and the specimen was loaded in axial compression.

(a) Plot the Mohr circles at tailure and determine b trom the LU tests tor the normally consolidated portion of the failure envelope.

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(b) For the CU test, plot curves of principal stress difference and pore pressure versus strain.

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(c) Assuming that the single CU test for which data are given is representative for CU tests run at pressures well above the preconsolidation stress:

(a) What is ɸ in terms of total stresses above the effects of preconsolidation? (b) What is ɸdetermined by the CU test above the effects of preconsolidation?

(After A. Casagrande.)