Determination of the critical size for stability analysis of soil-rock mixture slopes

Soil-rock mixture (SRM) slopes usually exhibit a significant heterogeneity due to distinct strength characteristics between rock aggregates and the soil matrix. The stability of SRM slopes relies on the coarse fraction, the nature of rock aggregates (particle size distribution and shape), and the relative size between the slope and the aggregates. However, the size effect of rock aggregates on the SRM stability is seldom reported, and its mechanism remains unclear. To this end, a total of 550 numerical simulations are performed to determine the critical sizes for evaluating the stability of SRM slope based on finite element methods. The critical sizes are subsequently analyzed considering the influences of coarse fraction, the aggregate shape, and the gradation. There is obvious variation in plastic weak zones among samples with the same mechanical properties, induced by the nature and spatial positions of rock aggregates, resulting in the oscillation of safety factors in parallel tests. Our study suggests that the critical size is positively correlated with coarse fraction and the coefficient of uniformity (Cu). An empirical equation is developed to predict the critical size from both coarse fraction and Cu. These findings provide a reference for critical size determination and reliable design of SRM slopes.