Abstract: The principal stress axis rotation will accelerate the accumulation of pore pressure and plastic strain and influence the mechanical properties of soil. The cyclic triaxial test and cyclic torsional shear tests were carried out by using GDS-HCA test system. The influence of continuous cyclic rotation of principal stress on the accumulative plastic strain and pore pressure of saturated silty clay under consolidation were investigated. The amplitude of the dynamic shear stress, the area surrounded by the stress path of the heart, the amplitude of the cyclic stress amplitude increase with the increase of the cyclic shear stress ratio and cyclic stress ratio. The pore pressure ratio increases as vibration load cycles increasing before specimen damaged. The pore pressure dissipates rapidly after the specimen failure, and then the pores pressure ratio declines sharply. The axial cumulative plastic strain which produced by cyclic torsion shear tests is always greater than the cyclic triaxial tests. This indicates that the axial cyclic rotation of the principal stress axis will accelerate the accumulation of the axial strain of the specimen. The cumulative plastic strain increases with the increase of cyclic shear stress ratio and cyclic stress ratio. Large cyclic stress ratio results in significant cumulative plastic strain caused by the rotation of the shaft. The accumulated plastic strain of saturated silty clay under consolidation and the cyclic rotation conditions of principal stress is established basing on the Monismith power function model. The reliability of the model is analyzed and verified.

Key words: rotation of principal stress, consolidated saturated silty, cyclic torsion shear tests, pore pressure ratio, axial cumulative plastic strain