True triaxial tests on frozen sandy soil under different intermediate principal stress coefficients and negative temperatures

To study the mechanical properties of frozen soil under complex stress paths, the effects of negative temperature and intermediate principal stress coefficient (b_f) on the strength and deformation characteristics of frozen sandy soil are studied by using the self-developed true triaxial apparatus. The test results show that the stress-strain relationship under different b_f values exhibits strain hardening characteristics under three dimensional stress states. The failure strength increases with b_f increasing from 0 to 0.5 and then decreases when b is in the range of 0.5~1. However, the values are still greater than those under the axial-symmetric stress state (b_f = 0). The strength increases linearly with the decline of the negative temperature. With the increase in b_f, the deformation in the direction of the intermediate principal stress changes from dilative to compressive and that in the direction of the minor principal stress remains dilative throughout. All the volumetric strain curves demonstrate the characteristics of shear shrinkage first and then dilatancy. The test points in the range of 30%~95% stress level are suitable for calculating the Duncan-Chang model parameters.