冻融作用对兰州黄土力学性质的影响

以兰州黄土为研究对象，让土样在封闭系统下经历一个冻融循环，再考察土的强度参数（c,φ）和前期固结压力（Pc）在冻融作用下的变化规律。试验表明，冻融循环对不同干容重的土具有强化和弱化的双重作用，并由此导致其力学性质发生相应的变化。相同冻结温度梯度下，随着土样干容重的增大，冻融后Pc和c具有首先增大然后减小的规律，并存在一个临界干容重，在这个干容重下，土样经过冻融后Pc和c不发生变化；干容重较小时，冻融后φ变化不大，随着干容重的逐渐增大，φ有少许增大。同一干容重下，随着冻结温度梯度的增大，冻融后Pc变化量减小，c的变化量增大，而φ的变化不大（呈逐渐增大趋势）。冻结温度梯度对力学性质的影响，主要是孔隙水的不同冻结方式造成的。

Influence of freeze-thaw on mechanical properties of Lanzhou loess

It has become a common understanding that freeze-thaw cycling is a kind of weathering process which considerably changes geotechnical properties of soils due to cryogenic actions. Therefore, the influence of freeze-thaw must be taken into account when selecting soil parameters for stability and deformation analysis of many geotechnical engineering problems in cold regions where newly exposed soil layers are bound to be submitted to freeze-thaw cycling. The changes in strength parameters (c, φ) and pre-consolidation pressure (Pc) due to freeze-thaw are investigated through testing on a frost-susceptible soil, Lanzhou loess within a wide range of dry density and temperature. The soil samples have all experienced one freeze-thaw cycle. Direct shear and 1-D compression tests are carried out on the samples before and after freeze-thaw. Testing results before and after freeze-thaw are then comparatively analyzed. It is shown that the pre-consolidation pressures and strength parameters are influenced by freeze-thaw.