Abstract
A comprehensive laboratory program was carried out on specimens trimmed from 152 mm diameter piston samples of a soft silty clay and a varved clay at a tunnel site in Thunder Bay. Results of conventional triaxial tests as well as special tests for the determination of anisotropic elastic parameters, simple shear tests, and stress path tests are presented.Results indicate that the unloading moduli are about twice the loading moduli, the Poisson's ratios in unloading are about three times those in loading, but the independent shear modulus is relatively unaffected. While the modulus is sensitive to mode of consolidation, drainage, and direction of stress path, the stress states at failure of all the different types of tests fall close to a single envelope for compression and extension. The choice of soil parameters for the analysis of deformation in tunnelling in soft clays is discussed. Key words: clay, tunnelling, stress path, deformation modulus, shear modulus, anisotropic elastic parameters, failure envelope.
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