The Research Of Shear Strength Tests Of Expansive Soil With Dry-wet Cycle Simulation And Lower Stress Condition

Shallow layer is a main characteristic of expansive soil slope failure under the effect of atmospheric dry-wet circulation. The cut slope surface collapse sliding frequently occurred where highway across the expansive soil area after a rainy season, it brought a great economic and ecological loss. So it is very important to evaluate the law of shallow layer failure about expansive soil slope and put forward a theory of effective treatment. This paper based on the national science foundation and project of expansive soil embankment treatment in Nanning outer ring expressway, and to develop the research of shear strength tests of expansive soil with dry-wet cycle simulation and lower stress condition.Firstly, the depth of sliding surface is generally not more than 3 meters, so it is necessary to discuss the soil strength under lower stress. In addition, conventional dry-wet circulation process does not take into account different position of slope on overlying pressure, only by improving test plan and controlling conditions can we more closely to simulate actual site situation. The sample preparation instrument was self-made and the correctness of the slow shear was verified.The expansive soil of Nanning outer ring was carried out slow shear on the direct shear apparatus according to the experimental plans. It obtained the test results of undisturbed and remolded samples after dry-wet cycles. The sectional double line method is adopted to approximate reflect the nonlinear characteristics of expansive soil strength, and it also can use the method to calculate the section index of shear strength c and (p. Furthermore, it also studied dry-wet circulation effect to the influence of strength reduced, and the reasonable effectiveness of new test method was verified.In order to further inspect common rationality of the new test, choose the expansive soil of Baise and Beijing to do the same test. By analysis of strength data of 3 kinds of expansive soil, the results show that:dry-wet circulation effect has a similar influence on all types of expansive soil, and shear strength is suitable for using sectional double line to describe; the final strength of different expansive soil types will fall to the same range as long as the outside climate condition are the same; the data fitting of cohesive force reduction and dry-wet circulation times is closely to exponential function relationship, and the internal friction angle changes within a certain range; the basic cause of strength reduction of expansive soil is discussed.Finally, a slope of Nanning outer ring was carried on a numerical simulation, and then put the strength parameters into the FLAC2D modle, the result of shallow layer failure was correspond to the actual. In addition, the factors affecting cohesive force reduction was analysed by the theory of grey correlation. All these results have an important reference to analyzing the stability of expansive soil slope.