Creep characteristics and constitutive model for frozen mixed soils

The uniform settle caused by the permafrost creep is still the primary problem of engineering construction in cold region. To investigate the creep characteristics of frozen soils mixed with silty clay and coarse-grained sand, several triaxial creep tests of frozen mixed soils under different conditions (temperature, confining pressure, coarse-grained particle content) were performed, and the effects of the temperature, confining pressure and coarse particle content on the creep characteristics of frozen mixed soils were also analyzed. The results of the experiments indicated that when the confining pressure was low, the specimen exhibited an attenuation creep under a low-stress level (0.4–0.7) and a non-attenuation creep under a high-stress level (0.7–0.9). In contrast, when the confining pressure was high, the specimen had both initial and stable creep stages, but no the accelerated creep stage. The higher the content of coarse grains, the shorter the stable creep stage, and the easier to enter the accelerated creep stage for the specimen. Further, the long-term strength of frozen soils decreased with an increase in the content of coarse grains. Finally, a newly improved Nishihara model was proposed to consider both the hardening effect and damage effect by introducing both the hardening and damage variables, which can model the entire creep process of frozen soils modeled relatively easily. It was found that with the increasing content of coarse particle, both the strengthening and damaged effects in the creep process are reduced