处在季节性冻土区的膨胀土渠道极易受到冻融循环作用的影响，影响工程的稳定安全。为了探究冻融循环作用对膨胀土物理力学特性的影响，以南阳膨胀土为研究对象，开展了不同含水率条件下膨胀土试样的冻融循环试验，对经历不同冻融循环次数作用后的试样进行了变形测量、无侧限压缩试验和微细结构试验。结果表明，在冻融循环过程中含水率低的膨胀土体积变化规律表现为“冻缩融胀”，含水率高的膨胀土体积变化规律表现为“冻胀融缩”；冻融循环作用对膨胀土的应力应变曲线、强度和弹性模量有着显著的影响，尤其是第1次冻融循环作用；试样的含水率越高，膨胀土的力学参数受冻融循环作用的影响越大；试样的面孔隙度和孔隙定向度的变化规律与力学参数的大致呈负相关，说明冻融循环作用下土体内部微细结构的变化直接影响着膨胀土的力学性质。

Expansive soil channel in seasonal frozen region is easy to be affected by freeze-thaw cycles, so as to will affect its stability and safety. In order to explore the effect of freeze-thaw cycles on the physico-mechanical properties of expansive soil, Nanyang expansive soil is taken as an example, which is prepared with different water contents and then on which deformation measurement, unconfined compressive test and microstructure test are carried out after different freeze-thaw cycles. The results show that in the progress of freeze-thaw cycles, the volume change of expansive soil samples with low water content could be expressed as “frost shrinking and thaw expanding”, in contrast, the samples with high water content could be expressed as “frost expanding and thaw shrinking”. Freeze-thaw cycles affected heavily the stress-strain curve, strength and elastic modulus of expansive soil, especially the first freeze-thaw cycle. The higher the water content of the expansive soil sample is, the greater the degree of its mechanical parameters affected by freeze-thaw cycles is. The relationship between porosity and pore orientation and mechanical parameters of expansive soil samples is generally negatively correlated, which can be inferred that the change of microstructure of expansive soil affected its mechanical parameters directly in the progress of freeze-thaw cycles.