It’s important to study the variation of shear strength and parameters of pile-soil interface for clayey soil with the excess pore water pressure in engineering practice. A series of direct shear test with different interface roughness

water contents and shearing rates is performed using the large-scale direct shear apparatus with constant normal stiffness. The effect on excess pore water pressure is examined under different test conditions. Influence of excess pore water pressure on shear strength of pile-soil interface in clayey soil is obtained. The results show that the excess pore water pressure decreases

and the shear strengths of pile-soil interface

effective cohesion and effective coefficients of friction increase with the increasing interface roughness. The excess pore water pressure increases and the shear strength of pile-soil interface decreases with the increasing water content. The main influence of increasing water content on shear strength of pile-soil interface is changing the cohesion. The cohesion first increases and then decreases. The influence on the coefficients of friction of pile-soil interface is little. The excess pore water pressure increases and the shear strengths of pile-soil interface also decrease with the increasing shear rate. The cohesion of pile-soil interface first increases and then decreases

but the variation is less than 2 kPa

and the little influence on the coefficients of friction of pile-soil interface. The change of shear strength and parameters is influenced by variation of excess pore water pressure

depending on interface roughness

water contents and shear rates. This experimental research is useful for relative engineering design.