Rainfall Infiltration Process of a Rock Slope with Considering the Heterogeneity of Saturated Hydraulic Conductivity

In order to analyze the effects of rainfall events on the stability of an open-pit rock slope, with considering the spatial variability of saturated hydraulic conductivity, based on the unsaturated seepage theory and the random filed theory, modified functions of the unit saturation, the hydraulic conductivity (k), and the shear strength parameters are established for unsaturated slope, by using FISH and the non-intrusive stochastic method. A saturated-unsaturated seepage random field model is proposed. And then the impacts of the rainfall intensity, the rainfall duration, and the spatial variability of saturated hydraulic conductivity (ks) on the infiltration process and stability of the unsaturated rock slope are analyzed. The results show that the proposed model can estimate rainfall infiltration of rock slope accurately. Rainfall mainly affects the seepage field in the shallow layer of the slope, where a transient saturated zone can be formed. With the development of the rainfall duration, the weight of the rock mass increased, the matric suction reduced, the negative pore pressure, the degree of saturation, and the infiltration depth of the rock slope increased, and the water in the slope root connects with the initial water table gradually, the unsaturated zone shrinks, which causes the safety factor of the model decreases, but the trend of change slows down gradually. As the rainfall intensity strengthened, the infiltration depth increased and the safety factor of the slope reduced, while the changing rate increases first and then decreases. Increasing the correlation length of k can reduces the infiltration depth and safety factor of the slope. Increasing the variation coefficient of k will increase the infiltration depth, while the safety factor of the slope decreases. The infiltration depth and safety factor of the slope are most affected by rainfall duration, but its sensitivity to the variability coefficient of k will be strengthened when the rainfall intensity exceeds the infiltration capacity. This conclusion can provide reference significance for the risk estimation of slope geological hazards, which are induced by the rainfall infiltration.

Soil-Water Characteristics and Creep Deformation of Unsaturated Expansive Subgrade Soil: Experimental Test and Simulation

The creep deformation of expansive soil has been considered as a vital threat to the safety in engineering construction because it may cause serious slope diseases in geological engineering. Meanwhile, since expansive soil usually remains in unsaturated state, its mechanical property is significantly affected by the seasonal environment. Therefore, the nonlinear deformation of expansive soil has received increasing attention, especially the humidity-dependent creep properties. This study focused on the stability of the unsaturated expansive soil subgrade considering rainfall and the creep behavior. Pressure plate extractor and direct shear tests were performed to investigate the hydro-mechanical and creep characteristics of the unsaturated expansive soil. Both the Van-Genuchten and Burgers models were applied to analyze the test results and inserted into the numerical model of the slope under rainfall infiltration. Results show that the compaction degree and the stress state was closely related to the water holding capacity of the expansive soil. The nonlinearity of the creep behavior became increasingly obvious with the increase of time and the stress level. The safety factor of the slope decreased as the rainfall time increased, and the most dangerous slide of the slope moved toward the foot of the slope. Considering the long-term creep process, there was a period of rapid growth in horizontal displacement that is detrimental to the stability of the slope. Besides, the rainfall infiltration could accelerate the slope failure before and after this creep process.