Abstract： Unloading effect of the deep excavation would decrease the pile’s bearing capacity and increase the tensile in pile shaft. A novel test system which can control the soil stress state was developed to study the pilesoil interactive behavior. In this novel system, the normal stress on the pilesoil interface is applied by the air pressure in the triaxial cell. The soil stress along the pile axis and the movement of model pile are controlled by the double piston. The pore pressure and water flow in the soil sample are adjusted by the two water cannels on the test cell. With the monitoring part of the system, the total shear force on the interface, the relative movement of the pile, and the deformation of the soil layer can be measured during tests. The triaxial interface tests show that the limit friction resistance and friction coefficient increase with the increase of the confining pressure, and the displacement of soil also increases with the increase of the confininig pressure.
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