冻融循环下滑坡古土壤细微观结构及力学性能研究

黄土与红黏土这一地层结构组合在黑方台地区普遍存在，黄土与红黏土之间存在渗透差，在持续灌溉条件下红黏土层会出现滞水效应，从而发生层带软化现象，最终诱发滑坡。本文分别开展室内土工试验、核磁共振试验(NMR)以及颗分试验，进而研究增湿条件下黄土-红黏土界面处非饱和入渗情况以及充水孔隙变化规律。得出以下结论：(1)在入渗过程中充水孔隙体积分布曲线中峰值不断向右迁移，充水孔隙半径不断增大且分布范围逐渐变广。黄土-红黏土组合样与纯黄土相比，充水孔隙体积分布曲线中最大峰值向右迁移较慢且分布范围较窄，入渗结束后红黏土层富含水分。(2)在相同流量条件下，黄土-红黏土组合样初始含水率越高，充水孔隙体积分布曲线中最大峰值向右迁移得越慢，所对应的充水孔隙半径变化越小且在界面处滞水效应越不明显。在相同初始含水率条件下，流量越大，充水孔隙体积分布曲线中峰值向右迁移得越快，水分进入中大孔隙越多且在界面处滞水现象越明显。(3)黄土-红黏土组合样在增湿过程中发生颗粒运移，导致颗粒间接触方式发生改变，最终试样底部细颗粒含量较多，界面处粗颗粒含量较多。

Study on changes of fine microstructure and macro-mechanical properties of landslide paleosoil under freeze-thaw cycle

The stratum structure combination of loess and red clay is common in Heifangtai area. Loess and red clay have penetration differences. Under continuous irrigation conditions,the red clay layer will have a water stagnation effect,which can cause layer softening and eventually induce landslides. In this paper,indoor geotechnical tests,NMR and particle fractionation tests were carried out respectively to study the unsaturated infiltration situation and pore change law at the interface between loess and red clay. The analysis of the test results show the following findings. (1)During the infiltration process,the peak value of the water-filled pore volume distribution map keeps moving to the right. The radius of the water-filled pore increases and the distribution range gradually becomes wider. Compared with pure loess,the maximum peak value in the water-filled pore volume distribution curve of the loess-red clay composite sample migrates more slowly to the right and has a narrower distribution range. The red clay layer is rich in water after the end of infiltration. (2)Under the same flow conditions,the higher the initial water content of the loess-red clay composite sample,the slower the peak value in the water-filled pore volume distribution curve shifts to the right,the smaller the change of the corresponding water-filled pore radius,and the water entering the medium and large. The fewer the pores,the less obvious the water stagnation effect at the interface. Under the condition of the same initial water content,the larger the flow rate,the faster the peak value in the water-filled pore volume distribution curve shifts to the right,and the corresponding water-filled pore radius is larger. The more water enters the medium and large pores,and the more obvious the phenomenon of water stagnation at the interface. (3)Particle migration occurs during the humidification process of the loess and red clay composite samples,which leads to changes in the contact mode between particles and the pore structure. The final sample contains more fine particles at the bottom and more coarse particles at the interface.