冻融对粉砂土力学特性及路堤边坡稳定性的影响

Effects of freeze-thaw cycles on mechanical properties of silty sand and subgrade slope stability

为研究粉砂土路堤在冻融循环作用下的力学特性以及采用粉砂土填筑的路堤边坡稳定性,基于静三轴试验,研究了不同含水量状态下,季冻区粉砂土在经历不同次数冻融循环后的粘聚力、内摩擦角等宏观力学特性的变化规律。以此为依据,采用有限元数值模型,针对不同坡度和不同填土高度对应的粉砂土填方路基,进行了冻融循环作用对边坡稳定系数的影响规律研究。研究结果表明:随含水量增大,冻融循环次数对粉砂土粘聚力的影响程度逐渐增强,当含水量较大时,粘聚力下降70%~80%;随冻融循环次数增加,粉砂土内摩擦角先降低,后略有增大;随含水量增大,冻融循环对粉砂土内摩擦角的影响有减弱趋势;冻融循环作用可使粉砂土路堤边坡稳定系数明显降低,冻融后的边坡稳定系数最大降幅可达到冻融前的49%;季冻区粉砂土路堤的最大填土高度不应超过4 m,小于3 m的填方路堤,极限坡度不应陡于1∶1.5,超过3 m的极限坡度不应超过1∶2.5。

In order to study the mechanical properties of silty subgrade and the silt subgrade slope stability under the freeze-thaw cycles,the static triaxial test was conducted with different water contents to study the variation law of the cohesion and the internal friction angle of silty sand after different numbers of freezethaw cycles in seasonally frozen area. The influences of freeze-thaw cycle on silt subgrade slope stability coefficient of the different slopes and different fill heights were analyzed by the finite element numerical model based on the test results. The results show that the influence of freeze-thaw cycle on cohesion of silty sand is gradually enhanced with the increase in water content,the cohesion can be reduced 70%-80%when the water content is large. The internal friction angle decreases firstly and then increases slightly with the increase in the number of freeze-thaw cycles,the influence of freeze-thaw cycles on the internal friction angle of silty sand is weakened with the increase in water content. The silt subgrade slope stability coefficient is decreased by the freeze-thaw cycles and the largest decrease after freeze-thaw cycles can reach49% of stability coefficient without freeze-thaw cycles. The maximum fill height of silt subgrade should not exceed 4 meters in seasonally frozen area. If the subgrade fill height is less than 3 meters,the limit slope should not be steeper than 1∶1.5. If the fill height is more than 3 meters,the limit slope should not exceed 1∶2.5.