Multiaxial creep of frozen loess

• Three types of tests were conducted on frozen loess under complex thermo-mechanical conditions in order to investigate the rate-dependent strength and deformation behavior.
• Hyperplasticity theory is applied and further extended to rate-dependent materials for establishing the constitutive model of frozen loess.
• The predictive capability of the developed constitutive model is verified by the multiaxial creep response of the frozen loess under three temperatures.

A series of triaxial compression and creep tests were conducted on frozen loess under different confining pressure and temperature conditions in order to study the rate-dependent mechanical behaviors. Experimental results illustrate that uniaxial instantaneous strength and long-term strength both follow the same variation rule with change of temperature over the range studied. The frozen loess exhibits prominent dilatancy behavior under low confining pressures. When the stress level exceeds the long-term strength, the mean dilatancy coefficient has a tendency to constant value in stable creep stage. The parabola-shape strength loci of frozen loess in mean stress-effective stress space were determinated experimentally. This testing result is more in agreement with the Ma's yield criterion for frozen soils (Ma et al., 1993). In order to establish the rate-dependent constitutive model of frozen loess, the hyperplasticity theory with multiple internal variables is applied and further extended to rate-dependent materials in this investigation. The predictive capability of this theoretical model, considering the effect of the pressure crushing and melting phenomena, is verified by the stress–strain-time behavior of the frozen loess in triaxial creep tests.