基于核磁共振下的冻土–结构正融过程界面特性研究

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

升温解冻导致冻土–结构相互作用发生劣化,为探究正融过程中冻土–结构相互作用,基于NMR分层测试技术对正融过程中界面未冻水含量进行测试,得到界面温度–未冻水含量变化规律;同时开展不同法向压力下界面剪切试验,得到界面温度–抗剪强度相关关系,从而进一步探究界面温度–未冻水含量–抗剪强度之间的内在联系。结果表明:NMR分层测试T2曲线可从微观尺度对界面融化过程进行表征,即正融过程界面小孔隙冰晶体融化开始,随着融化程度的加深大孔隙的冰也开始融化,最后直至界面处冰完全融化。根据界面温度–未冻水含量–抗剪强度的变化特征可将整个正融过程划分为冻结阶段、相变阶段、融化阶段3个阶段。依据莫尔–库仑破坏准则分析可知,正融过程中界面内摩擦角、黏聚力呈"此消彼长"的变化特征,其中随着解冻程度加深界面内摩擦角呈先减小后增大,而界面黏聚力呈现先增大后相对减小。

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.