A biaxial compression device has been developed to investigate the strain softening and failure characteristics of overconsolidated clay. Cell pressure from the triaxial compression test apparatus and a rigid loading platen are used to apply the minor and major principal stresses, respectively, to the clay specimen. The specimen is mounted inside the device, which fully restrains any out-of-plane deformation by means of a pair of thick perspex confining plates. Some results of testing are presented and compared with corresponding critical state model prediction.


Constitutive relations form an important basis of soil mechanics. In this connection, the failure of soil is a significant aspect of its mechanical behaviour. Localized failure which is commonly observed in foundation, slope and retaining wall works is manifested by large shearing deformations within a thin layer of material, known as the shear band, which is often accompanied by dilation. Heavily overconsolidated clays fall on the dry side of critical state and develop discontinuities when loaded to failure. The occurrence of such failure zones affects the numerical implementation of the constitutive equations of soils and the experimental techniques for determining the corresponding material parameters. Even though localized failure zones have been observed frequently during the failure of geotechnical structures, as well as following the peak loading of soil test specimens, it was only fairly recently that systematic studies were undertaken to analyze and describe their occurrence and patterns (Drescher et al., 1990). The theoretical studies focus on predicting shear-band initiation (Vardoulakis, 1980). The experimental efforts are an even earlier stage of development and concentrate on reproducing shear bands under laboratory-controlled conditions. Consequently, the database for localized failure in soils is rather limited and pertains to particular soils and loading conditions only (Vardoulakis and Goldscheider, 1981).

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