(1. School of Civil Engineering，Lanzhou Jiaotong University，Lanzhou，Gansu 730070，China；2. School of Railway Technology，Lanzhou Jiaotong University，Lanzhou，Gansu 730070，China；3. National and Provincial Joint Engineering Laboratory of Road and Bridge Disaster Prevention and Control，Lanzhou，Gansu 730070，China)
Abstract：The shear behavior of the contact interface between frozen soil and pile is an important basis for establishing the frost jacking calculation model of pile in frozen soil regions. A series of negative temperature direct shear tests of frozen sand soil and concrete with different ice film thickness at the contact interface were carried out to analyze the influence of ice film thickness on the shear mechanical deformation characteristics of the interface. Combined with multiple regression method，a trilinear shear constitutive model with multiple factors was established. Based on the shear-displacement method，the trilinear shear constitutive model is introduced to establish a theoretical calculation model for the frost jacking behaviour of single pile during the process of unidirectional freezing of seasonal frozen soil，and an example is analyzed. The results show that the ice film thickness has a significant effect on the shear behavior of the interface，and the relationship between the peak shear strength and the residual shear strength and the ice film thickness can be approximated as hyperbolic functions. The shear constitutive model can better reflect the effects of interface temperature，normal stress and ice film thickness on the shear behavior of frozen soil-concrete interface. Some pile-soil interface will slip during the freezing process of the soil around pile，and the peak position of tangential frost heaving force moves downward with the development of frost depth. The thickness of ice film has significant influence on the frost jacking effect of pile foundation. The frost jacking force does not increase linearly with the increase of frost heaving ratio，which is mainly affected by the shear strength between pile and frozen soil.
