冻融循环下非饱和膨胀土一维土柱模型试验研究

Experimental study on one dimensional soil column model of unsaturated expansive soil under freeze-thaw cycles

通过一维土柱模型对非饱和膨胀土进行冻融循环试验,分析了冻融循环过程中不同深度处温湿度、土压力、孔隙水压力和竖向位移的变化规律.试验结果表明:(1)土体在冻结过程中温度可分为过冷、跳跃、恒定、递降和稳定5个不同的变化阶段,存在明显跳跃点和冻结点,而升温过程并无明显的过热或突变现象出现.(2)冻结过程中,未冻水含量随温度下降逐渐降低,土体冻结点之后未冻水含量降低速度变快,整个冻融过程始终有未冻水存在.整个冻融过程中不同深度处的土体的温度和未冻水含量的变化均存在滞后现象.(3)温度场和水分场的变化会导致土体应力状态的改变,从而导致土压力和孔隙水压力的变化.其中第一次冻融对土压力和孔隙水压力的影响最大,随着冻融循环次数的增加变化渐缓.(4)冻融过程土体的竖向位移会发生波浪形变化,其中水分相态的转变对位移的影响最大,土颗粒及矿物成分的热胀冷缩带来的影响最小.

This paper uses a one-dimensional soil column model to carry out freeze-thaw cycle tests on unsaturated expansive soils,and analyzes the changes in temperature and humidity,earth pressure,pore water pressure and vertical displacement at different depths during the freeze-thaw cycle.The test results show that:(1)During the freezing process,the soil temperature can be divided into five different stages:supercooling,jumping,constant,descending,and stable,and there are obvious jumping points and freezing points.There is no obvious overheating or sudden change during the heating process.(2)During the freezing process,the unfrozen water content gradually decreases with the decrease of temperature.After the freezing point of the soil,the unfrozen water content decreases faster,and there is always unfrozen water throughout the freezing and thawing process.There is a hysteresis phenomenon in the changes of soil temperature and unfrozen water content at different depths throughout the freeze-thaw process.(3)Changes in the temperature field and moisture field will cause changes in the stress state of the soil,which will lead to changes in earth pressure and pore water pressure.Among them,the first freeze-thaw has the greatest influence on these two pressures,and the changes gradually become slow with the increase of the number of freeze-thaw cycles.(4)During the freezing and thawing process,the vertical displacement of the soil will change in a wave shape.The transformation of the water phase has the greatest influence on the displacement,and the thermal expansion and contraction of soil particles and mineral components have the least influence.