A thesis submitted in partial fulfillment of the requirements for degree of Master of Engineering in Asian Institute of Technology, Bangkok, Thailand

Thesis (M.Eng.) - Asian Institute of Technology, 1975

An investigation of the shear strength characteristics and stress-strain behaviour of Soft Nong Ngoo Hao Clay in extension was performed on isotopically consolidated triaxial specimens under undrained and drained conditions. All tests were divided into two types; one is the loading test (wherein the lateral pressure was increased keeping the axial pressure constant), the other was the unloading test (wherein the lateral pressure was kept constant while the axial stress was decreased). All tests were carried out under strain controlled conditions. Comparison of the stress-strain behaviour and the strength characteristics between the loading and the unloading tests are made for undrained tests. The results from the undrained loading tests on soft clay under extension was also compared with the corresponding data obtained under compression by other research workers. Similarly comparisons were also made between the drained loading tests under compression and extension conditions. The normalized stress-strain behaviour and the state paths followed by the specimens are found to be unique for all specimens sheared under similar applied stress paths. For each series of specimens tested under similar condition, unique water content strength relationship are al so obtained. For undrained loading tests, the angle of internal friction in compression and in extension are 27.0° and 19.6° respectively. Similarly for drained loading tests, the value of J in compression and in extension are 23.6° and 26.2° respectively. For unloading extension tests the value of c and under undrained condition are 8.5 psi and 20.2° respectively, the corresponding values under drained condition are 4.6 psi and 23.5° respectively. Finally, wherever possible the experimentally observed strains are com pared with the theoretical predictions.