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In a strong earthquake, not only a large number of coseismic landslides are triggered, but relaxation and cracks in the rocks and soils are induced, which make these rocks and soils vulnerable to instability during subsequent rainfall; thus, strong earthquakes always have long-term effects on landslides. The geo-hazards along the Zhaotong-Qiaojia road in the 2014 Ludian earthquake (Ms 6.5) of Yunnan Province, China, were investigated, and the Ganjiazhai giant landslide was chosen as a case study. First, using the limit equilibrium analysis and Newmark method, the critical seismic intensity of the landslide before the earthquake was evaluated. Secondly, the dynamic failure process of the landslide under the measured ground motion was simulated with the discontinuous deformation analysis method. Lastly, based on stress–seepage coupling analysis and precipitation data from Ludian meteorological station, the stability of the landslide during subsequent rainfall after the earthquake was predicted. The results show that the critical seismic intensity was within degrees VIII–IX, which is consistent with the results of the earthquake damage investigation. The dynamic failure process can be divided into four stages, and four scarps formed; the potential sliding zones during the subsequent rainfall were at the first scarp and the fourth scarp, and their critical rainfall amounts were 35–40 mm and 55–60 mm, respectively. In this paper, failure process simulation and stability prediction of the landslide before, during, and after the strong earthquake are presented, which provide analysis methods for the dynamic stability of landslides in the meizoseismal area. [ABSTRACT FROM AUTHOR]

Earthquakes are a major landslide trigger, and evaluation of the dynamic stability of landslides under seismic action is very important. The Yanyangcun landslide, which is located at route marker K92 of the Xianggelila to Lijiang expressway in Yunnan Province, China, was chosen as a case study. Using the three-dimensional finite difference method and the unbalanced thrust method, three mechanical indices of the sliding zone, including the volume ratio of the elastic or plastic elements, the permanent displacement, and the residual thrusts of the slices, were calculated to evaluate the progressive failure and dynamic stability of the landslide when exposed to different intensities of seismicity. The safety factor of the landslide with reinforcement measures was also assessed. The critical peak seismic acceleration was about 2.29 m/s2, between earthquake intensity of VIII degree and IX degree. The landslide experienced progressive failure by means of shear at the leading edge, tension at the trailing edge, and immobilization of the middle part. The middle part of the sliding zone underwent a "locking effect," which could effectively resist the immobilization of the plastic zones of the leading edge and the trailing edge. With reinforcement measures, the dynamic stability of the landslide under VIII degree and IX degree events satisfied the allowable safety factor of the local specifications. The results provide guidance for disaster prevention and aseismic design for the Yanyangcun landslide, and can also be used as reference information for dynamic stability evaluation of other landslides threatened by earthquakes. [ABSTRACT FROM AUTHOR]

The stability of a colluvial slope, which is different from a rock or soil slope, is determined by the properties of both the bedrock and the colluvium. Coupled with artificial excavation and environmental effects, the stability factors of such slopes are complicated. To rapidly and effectively evaluate the risk of a colluvial cutting slope, a risk evaluation system for this type of slope is established herein. First, an evaluation index system is established, and reasonable risk evaluation indices are selected. Second, the fuzzy analytic hierarchy process (FAHP) is applied, a fuzzy pairwise comparison matrix, that must satisfy a consistency test, is constructed, and the weight of each index is determined. Third, the risk evaluation grades are divided into 4 risk grades, and the risk evaluation criteria for each basic index are determined. Finally, the three-level fuzzy comprehensive evaluation (FCE) method is applied, the membership function for each index is constructed, the membership degree is calculated, and the risk grade of the colluvial cutting slope is determined. This risk evaluation system is used to evaluate the risks of 148 colluvial cutting slopes along the Xiaomengyang-Mohan highway in Yunnan, China. The results show that there are 24 slopes of low risk (grade I), 85 of medium risk (grade II), 22 of high risk (grade III), and 17 of very high risk (grade IV). The evaluation results obtained are in good agreement with the actual slope instability states: failure occurred in 15 out of 85 slopes of risk grade II, 13 out of 22 slopes of risk grade III, and 16 out of 17 slopes of risk grade IV. This application demonstrates that the proposed risk evaluation system for colluvial cutting slopes is universal, and stable and that the calculation results are objective. [ABSTRACT FROM AUTHOR]

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]