冻融循环下压实度对粉质黏土力学性质影响的试验研究

 冻融循环是冻土地区路基填料性能劣化的主要因素之一。以压实度和冻融循环次数为主要变量，对青藏高原粉质黏土力学性质的变化规律进行三轴试验研究。试验结果表明：初始压实度对粉质黏土力学性质的冻融效应具有显著影响。不同压实度试样的应力–应变曲线形式随冻融次数的增加趋于接近，并由应变软化型向硬化型过渡。封闭系统中试样的水分迁移会引起含水率的增减分区分布，低压实度有利于增大水分迁移量和含水率增高区的分布范围。冻融过程对高压实试样的破坏强度以降低为主，对低压实度试样则相反。在最优含水率附近，土体抗剪强度随含水率呈非线性变化规律，因此试样内部水分重分布也可能会导致强度的改变，且其作用效果受压实度影响具有不确定性，压实度较高时会导致试样黏聚力减小，压实度较低时则相反；不同压实度下内摩擦角均呈现增大的趋势，且压实度越低，变化幅度越大。冻融过程中，土体干密度和含水率变化对力学性质的影响是同时存在的，由于初始压实度和冻融次数的不同，对强度变化起主导作用的因素也不同。水分重分布是不同压实度土体力学性质冻融循环效应的整体趋势和具体过程呈现多样化的原因之一。

Experimental study on the effect of cyclic freezing-thawing on mechanical properties of silty clay with different degrees of compaction

The cyclic freezing-thawing is one of the main factors causing the performance deterioration of the subgrade filling material in cold regions. In order to identify the effect of the original compaction degree on the variation of mechanical properties of silty clay in Qinghai—Tibet Plateau，a series of triaxial tests were performed with different degrees of compaction under freezing-thawing cycles. The results show that the levels of original compaction degree affect considerably the freezing and thawing effect on soil mechanical properties. The forms of stress-strain relation of samples with different degrees of compaction are similar，changing from the strain softening to hardening after several freezing-thawing cycles. The water migration inside samples under the closed condition during the freezing and thawing lead to the partition of zones with the moisture content increase and decrease respectively. The sample with the lower compaction degree has a bigger zone with the moisture content increasing. The effect of freeze-thaw cycles on the failure strength decrease for the samples with high compaction degree，and increase for those with low compaction degree. The relationship between the shear strength and the moisture content can be expressed as a nonlinear function，and the redistribution of the moisture content inside the samples leads the change of overall shear strength. After the repeated cyclic freezing-thawing，the cohesion of samples with the high compaction degree decreases，while that with the low compaction degree increases. The internal angle of friction always increases after the redistribution of moisture content，and the lower compaction degree causes the higher increasing rate. Hence both the dry density and water redistribution affect the mechanical properties of samples，and their effects exist simultaneously during the freezing-thawing cycles. Which of these two factors played the leading role depends on the original compaction degree and the number of freezing-thawing cycles.