The interfacial force of the precast pile with different roughness was measured by indoor direct shear test in clayey soil. The changes of the pore water pressure and soil pressure on the pile-soil interface were monitored by miniature piezo-resistive sensors. The influences of interfacial roughness on interface shear strength parameter

interface resistance-shearing displacement curves were qualitatively analyzed. The results show that the percentage of normal stress accounted by pore water stress on pile-soil interface is about 10%

which is supposed to be taken into consideration in practical projects. The concept of pile-soil interface resistance is presented and the resistance is contributed by adhesive force and friction force between clayey soil and concrete. the friction force is the product of the normal effective soil stress and friction coefficient on the interface. As the interfacial roughness of the concrete increases

the interfacial adhesive force increases and gradually closes to clayey soil’s inherent adhesive force. The interfacial roughness slightly impacts on interfacial friction coefficient and interface resistance: the ultimate interface resistance and shearing displacement increase with the increase of the roughness. The results provide references to the design

construction and detection of the pile foundation engineering.