Long-term stability analysis of loess cutting shallow slope based on wet-dry cycle test

To evaluate the shallow soil strength deterioration effect of loess slope under wet-dry cycle, the laboratory direct shear tests were carried out under different wet-dry cycle paths on Q₃ undisturbed loess from Dingxi, Gansu Province. The effects of cycling times, cycling amplitude and lower bound water content on the shear strength of the soil were analyzed. A strength degradation model considering three parameters of wet-dry cycle was established, and the long-term stabilities of loess cutting shallow slope under different wet-dry cycle paths were compared by the strength reduction method. Test results show that the cohesion of undisturbed loess first decreases and then tends to be stable with the increase of wet-dry cycles, which can be fitted by the hyperbolic function. The internal friction angle decreases linearly. After 10 cycles, the maximum deterioration degrees of cohesion and internal friction angle are 27.64% and 9.88%, respectively. Under the same wet-dry cycles, the degradation effects of the cycling amplitude on the cohesion and internal friction angle of undisturbed loess are greater than that of the lower bound water content. The long-term stability coefficient of loess cutting shallow slope follows an exponentially decreasing function during the wet-dry cycle. The maximum reduction of slope stability coefficient under different wet-dry cycle paths is 61.5%, and the reduction of stability coefficient accounts for 85% of the total reduction after 6 cycles. The stability of loess cutting shallow slope is affected by the cycling amplitude and lower bound water content in the wet-dry cycle, which shows that the slope stability increases first and then tends to be stable with the increase of lower bound water content. However, with the increase of cycling amplitude, the stability coefficient decreases linearly. In engineering practice, the water content varies with the depth in the slope, and the wet-dry cycle paths are different, so the layering effect of wet-dry cycle should be considered in long-term stability analysis of loess cutting slope.