Strain- and stress-controlled shear strength behaviour of Kolkata clays

Shear strength of soil plays a crucial role in the estimation of bearing capacity of foundations and also for assessing the stability of slopes, dams and embankments, excavations, retaining structures and highway pavements. In this paper strain-controlled and stress-controlled consolidated undrained and drained triaxial tests were conducted on remoulded inorganic and organic clay available in Kolkata to examine and understand the variations in shear strength parameters due to testing procedures. The results show that the maximum deviator stress is higher for drained tests than that of undrained tests whereas the effective friction angle in case of undrained tests is greater than the drained tests by 4 degrees to 6 degrees for inorganic clays and 5 degrees to 8 degrees for organic clays. However, the effective friction angle in the case of stress-controlled tests are significantly higher than those obtained during strain-controlled tests for both inorganic and organic clays under-undrained conditions only.