Experimental research on pile-soil interface shear behaviors of super-long bored pile

A series of shear tests is carried out on the interfaces between concrete and silty clay, fine sand to study pile-soil interface shear behaviors of super-long bored pile using large-scale interfacial shear apparatus. Bentonite mudcake or bentonite mudcake and cement slurry are installed on the interfaces between fine sand and concrete to study the influence of mudcake and post grouting on the shear behavior of pile-soil interface. The results show that the shear stress increases nonlinearly with the increase of the shear displacement. After the shear stress reaches an ultimate value, the shear stress retains mainly a constant value or shows a softening tendency. The shear behaviors of the interface are significantly influenced by the soil type and the normal stress on the interface. The friction angle of interface between fine sand and concrete is close to the effective internal friction angle of the soil. The friction angle of the interface reduces 40% when the mudcake exists, showing that the lubrication action of the mudcake can greatly weaken the shear performance of interface. By grouting the cement slurry into the interface with mudcake, the friction angle of the interface increases nearly by one time that of the mudcake interface. It is shown that grouting not only can eliminate the adverse effects of mud cake, but also can further improve the shear properties of the interface. Furthermore, the relation between shear stress and shear deformation of the interface is closely related to mudcake and cement slurry. Due to the interface shear in the soils, a shear band is found to form gradually in soil near the interface. The phase of shear displacement gradually transforms into the phase of shear slipping during shear process. Moreover, there is great difference in the shear deformations of soils with different types of interface during shearing.