Abstract
Experimental studies were conducted to investigate the effect of disturbance due to sample preparation on the shear strength of cohesive soils. The variation of the pore-water pressure was monitored during consolidation, extrusion and trimming with an embedded small porewater pressure transducer. The unconsolidated and undrained compression tests and unconfined compression tests were carried out on trimmed samples and the pore-water pressure during shearing was also observed with the probe.The negative pore-water pressure observed immediately after the removal of the consolidation pressure of 98 kN/m2 compared well with the theoretical prediction. The negative pore-water pressure, the mean effective stress, decreased with the progress of sample preparation and remained at the constant value of about 30 and 20 kN/m2 for soil with plasticity index equal to 50 and 30 respectively. This is equivalent to the overconsolidation ratio of 3 and 5. The stress paths for shearing tests are analogous to those of overconsolidated samples. The comparison of the strength of trimmed samples with that of ideal samples shows that the mechanical disturbance reduced the undrained strength more than swelling. Due to the sample preparation the undrained strength reduced by 15% and 30% for soil with plastcity index of 50 and 30 respectively.
