Pore pressure characteristics of an extrasensitive clay

The results of a laboratory Investigation into the pore pressure characteristics of an extrasensitive marine clay are presented. The soil samples were obtained from the Port Mann area of British Columbia. Experimental work consisted of the performance of long-duration triaxial shear tests with pore-pressure measurements. A stress-controlled triaxial machine equipped with a null-indicating type pore-pressure device was employed for all shear tests. The observed data show that for this soil a slow build-up of pore pressure occurs for both increases in cell pressure and axial stresses in the triaxial test. Even in saturated specimens the slow build-up effect prevailed. The rates of build-up observed for changes in axial stress were slower than those recorded for changes in cell pressure. Measurements at the upper end of some specimens, and at the centre of others, indicated that the pore pressure required more time to reach equilibrium, at the ends of cylindrical specimens. The hypothesis is put forward that the observations can be explained by plastic deformations of the adsorbed layers surrounding the particles. Strength and pore pressure parameters have been obtained for the soil. An automatic control has been developed to assist in the performance of long-duration tests. The apparatus employs the photo-electric effect to control movements of pore water. A detailed description of this device is presented.Applied Science, Faculty ofCivil Engineering, Department ofGraduat