The shear strength behaviour of granular soils is affected by several factors such as void ratio, confining stress, soil fabric, strain history, loading mode and drainage conditions. In the current geotechnical design practice, the design soil parameters are obtained from laboratory tests either under fully undrained or fully drained drainage conditions. It is presumed that these two drainage conditions represent the extremes of soil response under shearing. This assumption of fully undrained or drained drainage conditions is possible only if the soil deposit is homogeneous and there is no pore pressure gradient exists within the soil deposit. But the actual soil encountered in-situ is highly heterogenous and this heterogeneity could result in a partially drained condition which involves simultaneous change in pore pressure and pore volume during shear loading.  This partially drained condition could trigger strain softening response of soil and might be more critical than the undrained conditions which is normally assumed for liquefaction analysis.

 Keywords: Hollow Cylinder Torsional shear test, Partially drained behaviour, Generalized loading
Considering the importance of the problem, this paper aims to investigate the partially drained response of Fraser River sand through hollow cylinder torsional shear tests.  The isotropically consolidated Fraser River sand specimens are sheared along target non-linear strain paths, with a fixed direction of principal stress axes and intermediate principal strain parameter. The non-linear paths adopted in this study expose the sand specimen to various drainage conditions, ranging from contractive to expansive drainage. The experimental results demonstrated that the softening tendency of soil is higher under expansive volumetric strain path which is more critical than the undrained drainage condition.