Interface characteristics of frozen soil-structure thawing process based on nuclear magnetic resonance

The temperature-thawing causes the permafrost-structure interaction to deteriorate. In order to explore the frozen-soil interaction laws during the thawing process, based on the NMR stratification test technology, the interface unfrozen water content in the process of thawing is tested, and the change of interface temperature-unfrozen water content is obtained along with its variety law. At the same time, the interface shear tests under different normal pressures are carried out to obtain the relationship between interface temperature and shear strength, and further to explore the intrinsic link among interface temperature, unfrozen water content and shear strength. The results show that the T2 curve of NMR stratification can characterize the interface thawing process from the microscopic scale, in other words, the melting of small pore ice crystals begins at the interface of the thawing process. As the melting depth deepens, the ice of the large pores begins to melt until the ice which is at the final interface completely melts. According to the change characteristics of the interface temperature-unfrozen water content-shear strength, the whole thawing process can be divided into three stages: freezing stage, phase change stage and melting stage. The analysis based on the Mohr-Coulomb failure criterion suggests that the internal friction angle and cohesive force of the interface during the thawing process change, which follows the law “as one falls, another rises”. And the internal friction angle decreases first and then increases with the degree of thawing, while the interface cohesive force first increases and then decreases relatively.