Abstract: Principal stress rotation is a kind of typcial stress path supplied to the ground,when it is subjected to wave or vehicle loads.In order to study the strength characteristics of silt under different combinations of principal stress orientation, a series of hollow cylinder sample tests were performed with saturated silt of Dr = 70% from the sea entrance of the Yangtze river. The tests include cyclic principal stress rotation (CPSR), cyclic triaxial (CT) and cyclic torsional shear (CS) tests. It is found that isotropic consolidated samples under the above tests would collapse at minor strain and liquefaction, which is featured by the excess pore water pressure reached initial effective confining pressure. And the effective stress states at collapse points could be normalized by the parallel quasi-instable lines in the p’-q space. As to the liquefied and collapse cycles, CS had the maxium and CPSR had the minimum under the same peak values of shear stress. Furthermore the collapse energy is put forward to evaluate the dynamic strength under different paths. It is shown that the energy is related to the kinds of stress paths but not shear stress level. And the collapse energy decreased in CS, CT and CPSR in turns, which matched the characteristics of increased effective confining pressure at the collapse points under these three paths. The adoption of collapse energy overcame the interference of nonunified shear stress level on the failure criteria under complicated stress path, in which the shear stress might be constant or change cyclically.

Key words: principal stress orientation, silt, high relative density, collapse energy, isotropically consolidation