Experimental and numerical investigations on the multi-stage creep behavior of frozen sand under stepwise loading and unloading

As temporary support in geotechnical and tunneling scenarios, frozen soil bodies are often subjected to varying stress states during different construction stages and techniques and, thus, exhibit stepwise loading and unloading, leading to multi-stage creep. However, experimental and numerical investigations on frozen soil creep behavior have focused primarily on monotonic loading, i.e., single-stage creep. This study expands an existing experimental database on stepwise loaded creep and introduces a unique test series focusing on the uniaxial creep behavior of frozen sand under stepwise unloading and load-unload cycles. Here, similar to stepwise loaded creep, the minimum creep rate is found to remain mostly independent of the loading history, while the corresponding frozen soil lifetime depends on the latter. In contrast to equivalent single-stage creep scenarios, the lifetime becomes longer for stepwise loaded creep and shorter for stepwise unloaded creep. To consider multi-stage creep in the geotechnical design of frozen soil bodies, based on our experimental database and literature data, we test the ability of two versions of an advanced constitutive model to capture the frozen soil creep behavior under varying stress states. Comparison of the extended version, called EVPFROZEN, with the original highlights the advantages of EVPFROZEN in consistently capturing the creep rate evolution and the practically important frozen soil lifetime under complex loading histories. Combining the insights from the novel experimental database with testing and validation of the advanced constitutive model EVPFROZEN advances the efficient and sustainable design of frozen soil bodies in geotechnical applications under multi-stage loading conditions.