干湿循环效应对南宁外环膨胀土抗剪强度的影响

针对膨胀土边坡滑坍多呈浅层破坏的现状,选取南宁外环膨胀土原状样与重塑样开展对比试验,精心设计试验方案,改进常规直剪试样制备条件和试验方法,使模拟土体季节性干缩湿胀过程更接近实际,探究了2种土样经历多次干湿循环作用后抗剪强度的衰减规律。结果表明：试样制备中有上覆荷载作用,实测土样经历同样干湿循环次数后的强度衰减幅度比无荷条件下的小,再次验证荷载对抑制强度衰减作用明显；不管原状还是重塑样经干湿循环后的强度衰减主要是c值大幅降低,其值虽也减小但降幅都不大；此外,计入边坡浅层破坏时滑面的低应力条件开展试验并分析测试结果,得到做边坡浅层稳定性分析时合理的抗剪强度参数,研究结果可供工程设计参考。

Influence of wetting-drying cycles on strength characteristics of Nanning expansive soils

Since most of expansive soil slopes exhibit shallow landslide, undisturbed and remoulded expansive soils of Nanning outer ring are specially selected to carry out contrast tests. Through the well-designed test program, by improving the conventional sample preparation conditions and methods of direct shear tests, laboratory simulation of soils under seasonal drying shrinkage and wetting expansion is made closer to the actual situation. Meanwhile, the rules of strength reduction of the two kinds of soil samples subjected to wetting-drying cycles are studied. The results show that the strength reduction ratio of the soil samples with loading is smaller than that of the soil samples without loading after experiencing the same wetting-drying cycles, which verifies that the loading has an obvious inhibitory effect on the shear strength reduction. Whether it is undisturbed or remoulded samples, the strength reduction is mainly owing to the decrease of c after experiencing wetting-drying cycles and the reduction of φ is not obvious. Moreover, taking the low stress of slope shallow layer sliding into consideration when conducting tests, by analyzing the test results, reasonable shear strength parameters can be determined to analyze the stability of shallow slope. The research conclusions can be used for reference in engineering design.