Miniature Piezocone Penetration Test Results in Cohesive Soils

The effects of penetration rate and filter element locations on the piezocone penetration and dissipation test results were experimentally studied. Ten piezocone tests were conducted utilizing U1 (filter element at the cone tip) and U2 (filter element above the cone base) miniature piezocone penetrometers. The calibration chamber tests were conducted on normally consolidated and heavily over-consolidated K33 specimens (mixture of 33 % kaolin and 67 % fine sand) under Ko conditions, and at penetration rates of 0.3, 0.6 and 2.0 cm/sec. The corrected net cone resistance and excess pore water pressure increased with the increase in penetration rate. The excess pore water pressure generated during penetration at U1 was larger than that generated at U2. The immediate (instantaneous) drop of excess pore water pressure at U1 and U2 locations, when penetration is arrested for pore pressure dissipation, was clearly identified by using a digital oscilloscope. The magnitude of the instantaneous drop in excess pore pressure affects the so-called “initial” pore pressures, and is influenced by pore pressure element location, speed of penetration and state of stress.