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Soil–rock mixture (SRM) shows complicated mechanical behaviors and hydraulic characteristics, which lead to challenging deposit landslides and debris problems in southwestern China. Previous studies have shown, based on several mechanical tests, that the strength parameters of natural SRM are sensitive to water content. Therefore, the complex mechanical characteristics during rainfall are vital when analyzing the deposit slope failure mechanism. This study aims to investigate the stability of a typical deposit slope in Yunnan, China that is subjected to different rainfall conditions given the parameter deteriorations and crack effect. A large scale mechanical laboratory is generally adopted to obtain the strength parameters of natural SRM to avoid the scale and boundary effects due to the particle size of the rock blocks inside that involves the consumption of time, materials, and money. Nonlinear empirical formulas to predict the deteriorated values for the cohesion and friction angles of natural SRM with a variety of water contents will be proposed in this study to address the shortage of laboratory tests. The accuracy of the formulas will be proved by comparing the estimated and measured values from previous studies. A series of two-dimensional (2D) numerical analyses will be conducted to study the effect of rainfall conditions and crack depths on deposit slope stability by considering the deteriorated strength parameters. The results indicate that the deposit slope stability gradually decreased during rainfall and the decreasing rate of the factor of safety increased as rainfall intensity increased. The comparisons between a slope with and without parameter deteriorations demonstrated that the weak resistance of SRM to water is a negligible factor in slope failures. The simulations of the cracking slope reveal that cracks could provide preferential flow channels for rainfall infiltration, which lead to the appearance of an increasing pore water pressure area and groundwater level fluctuations, which increases the probability of slope failure. As the crack depth increases, the influence of cracks on pore water pressure distribution and slope stability becomes more apparent. The combined effects of rainfall and crack depth on slope stability will be analyzed according to the simulation results. The results from this study could provide a reference to estimate deposit slope stability by considering parameter deteriorations that are subjected to rainfall and expand the understanding of the relationship between rainfall intensity, duration, and crack depth. [ABSTRACT FROM AUTHOR]