Characteristics of cumulative plastic strain and critical dynamic stress of frozen clay under principal stress rotation

As the foundation of cold region projects and the supporting wall of artificial freezing projects, the frozen soil often bears the disturbance of dynamic loads. Studying the cumulative plastic strain and the critical dynamic stress under the dynamic loads provide an important reference for the deformation design and stability evaluation of the cold region and artificial freezing projects. To reveal the influences of the principal stress rotation on the cumulative plastic strain and the critical dynamic stress characteristics of the frozen clay, a series of dynamic triaxial tests and pure principal stress rotation tests considering the influences of confining pressure are carried out by FHCA-300, and the characteristics of the cumulative plastic strain, the cumulative plastic strain rate and the critical dynamic stress of the frozen clay are analyzed. The results show that the axial cumulative plastic strain of the frozen clay increases with the increase of cycles, the increase of the confining pressure will restrain the development of its axial cumulative plastic strain, and the principal stress rotation will accelerate the development of its axial cumulative plastic strain. The evolution of the axial cumulative plastic strain rate of the frozen clay shows three different trends. The division criterion of plastic deformation behavior of the frozen clay based on the cumulative plastic strain rate is proposed, and the expressions for the critical dynamic stress of the plastic shakedown and plastic creep of the frozen clay are established. It is confirmed that the critical dynamic stress of the frozen clay decreases significantly under the rotation of the principal stress axis. The research results are of important guiding significance for the design, construction and stability evaluation of the frozen soil projects and the development of the resources in cold regions.