EXPERIMENTAL STUDY ON EXCESS PORE PRESSURE AND EFFECTIVE STRESS IN COHESIVE SOIL AFTER PILE FORMATION

For the soil compaction effect in a precast pile, the variation with time of excess pore water pressure and vertical effective stress at the pile-soil interface is analyzed by means of in-situ test and numerical simulation. The hydraulic fracturing theory, cavity expansion theory and modified Cam-clay (MCC) model are used in this study. The distribution of excess pore water pressure along the pile length during the consolidation process of soil around the pile is revealed. The results show that the excess pore pressure around the pile is proportional to the depth of the sensor, just like the pore pressure. Under the action of external load, the excess pore pressure and vertical effective stress in cohesive soil show a three-stage trend of “increase–decrease–level” and “level–increase–level” respectively with time. About 25 days after the pile is formed, the excess pore pressure is basically dissipated, and the vertical effective stress tends to the maximum value of stability. Based on the numerical model of the modified theoretical formula, under different loads, negative excess pore pressure appears in the middle and lower part of the pile side. The smaller the horizontal distance from the pile and the vertical distance from the pile end are, the greater the excess pore pressure is. It can provide reference for similar problems of soil squeezing effect of static pressure pile driving.