Development of pore pressures in quasi-static penetration tests in sensitive clay

Abstract

The static cone penetration test is a valuable tool for the investigation of soil deposits but its potential may be further improved in the future if the pore pressures generated around the cone tip during the penetration are measured.A new sounding instrument called a piezocone was built at Université Laval to investigate the magnitude, effects of rates of penetration, and rate of dissipation of the excess pore pressures according to the location of the porous stone on the apparatus.The magnitude of the pore pressures induced during driving is a maximum at the cone tip and then decreases along the shaft as measured by porous stones located behind the cone tip. Induced pore pressures at the tip are independent of the rate of penetration, but a very small rate effect may influence the pore pressures measured behind the cone tip. The results show that the use of the ratio u/qc for soil characterisation may be considered only after adoption of standards regarding the location of the sensing element and the rate of penetration.The new sounding tool models the penetration of a single pile relatively well and its use is suggested for the study of pore pressures during the penetration of piles and their dissipation with time.