考虑水分迁移影响的浅层膨胀土抗剪强度冻融劣化特征

冻融作用下的水分迁移及其伴生现象会使浅层膨胀土的抗剪强度发生劣化,探明水分迁移对浅层膨胀土抗剪强度的影响对于膨胀土工程冻融病害的防治是必要的。首先,模拟实际冻融边界条件开展膨胀土在单向冻结–双向融化作用下的水分迁移试验,在此基础上进一步开展膨胀土的直剪试验;试验过程中对土样的水分场、温度场、竖向变形均加以监测。研究结果表明:(1)冻结温度梯度对水分迁移量的影响较大,冻融后膨胀土表现出冻胀融沉的特点且融沉量略大于冻胀量;(2)抗剪强度的变化与含水量的重分布沿深度方向上表现出了高度的相关性,抗剪强度在含水量增高的冻土区均表现出衰减的特点,在含水量降低的未冻区则表现出小幅度增加的特点,抗剪强度变化幅度随含水量变化幅度的增加而增大;(3)沿土样深度方向上抗剪强度指标的变化特征与含水量的变化特征也表现出了较高的相关性,含水量降低区的抗剪强度指标均有小幅增加,含水量增高区中基本上都呈现出衰减趋势,黏聚力的大幅减小是膨胀土抗剪强度冻融劣化的主要原因。

Shear strength degradation characteristics of expansive soil during freeze-thaw process considering moisture migration

The shear strength of soil would be deteriorated by moisture migration and the accompanying phenomenon during freeze-thaw process. For the prevention and treatment of freeze-thaw diseases in expansive soil engineering,it is necessary to ascertain the degradation effect of moisture migration on the shear strength of expansive soil. By simulating real freeze-thaw boundary conditions,the moisture migration experiments of expansive soil under the axial freezing and bidirectional thawing action were carried out,and direct shear tests were conducted. The moisture field,temperature field and vertical deformation of expansive soil were monitored during the test. The research results show that the moisture migration quantity is influenced by the freezing temperature gradient,and that the expansive soil during freezing-thawing shows frost heave and thawing settlement characteristics and the thawing settlement is slightly larger than the frost heave. The variation of the shear strength has a high consistency with the water content redistribution along the depth direction. For specific performance,the shear strength of frozen soil attenuates when the water content increases,while the shear strength of unfrozen soil increases mildly with decreasing the water content. The variations of shear strength indexes and moisture field redistribution also show a high consistency along the depth direction. Specifically,shear strength indexes decrease when the water content increases. The attenuation degree of the cohesive force is significantly greater than that of the internal friction angle. The decrease of the cohesive force is the main reason of freeze-thaw deterioration the shear strength for expansive soil.