Xing-guo Yang

A Mathematical Model for Forecasting the Dam-Break Flood Routing Process of a Landslide Dam

Once a landslide dam bursts, its reservoir discharges quickly in a flood which will cause catastrophic damage to life and property downstream. For a specific landslide dam, the peak flow rate and the evolution of downstream flood are influenced by the shape and size of the dike breach when dam-break occurs. According to the general nature of landslide dams and field observations of dike-breach development patterns, a dike-breach propagation mode has been determined. By combining an improved empirical equation with knowledge of the dike-breach propagation mode, a mathematical model for forecasting dam-break flood routing has been developed and is presented here. Sensitivity analysis was then carried out based on the computed results for peak flow rate and the flood evolution curve under different parameters. The computed results showed that the width coefficient and the depth coefficient had similar effects on the dam-break flood but that the impact of the depth coefficient was more significant than that of the width coefficient. Finally, the proposed model was used to calculate the flood evolution for the Tangjiashan landslide dam. The computed results showed that the error between the simulated result and the measured data was less than 5%.

Experimental study of the impact factors of natural dam failure introduced by a landslide surge

A large amount of loose deposit between the sides of a landslide lake may slide into a reservoir at any time because of influences such as earthquakes, heavy rainfall or other triggering factors. These factors can cause the formation of a huge surge and result in the instantaneous failure of a landslide dam. The failure of a landslide dam can threaten people’s lives and property downstream. This paper analyzes the destruction mechanism of landslide dams because of a surge and the impact of the contact area, the landslide height, and the distance between the entry point and the dam site for a dam break through physical experiment and compares the experimental results with the calculated values. Experimental results show that the contact area and the landslide height have a significant impact on the dam-break surge. A measure based on the previously mentioned factors can be made to reduce the dam failure risk caused by a landslide surge. Two empirical methods (Pan’s method and Miller’s method) are used to predict the landslide surge wave and compared with the experimental results; the simulated results show that the Miller’s method used for predicting the landslide surge wave is more reasonable.

A reliability analysis method for rock slope controlled by weak structural surface

Catastrophic landslides maybe occur in rock slope due to the effect of strong earthquakes or heavy rainfall. The stability of rock slope is usually controlled by different scales of weak structural surfaces, which are uncertain and randomly exist in the rock slope. According to the geological characteristics of rock slope, two typical failure modes – plane and wedge are possible. A second-order second-moment (SOSM) method is presented to calculate the reliability index and the failure probability of rock slope, which is an improvement over the first-order second-moment (FOSM) method, and performance functions are built up with the classic limit equilibrium method. The presented method is applied to analyze the failure probability of two rock slopes at the Jinping I Hydropower Station and is compared with the Monte Carlo method and the FOSM method. The computed results show that for plane failure, the reliability index and the failure probability determined by the presented method are 0.563 and 28.7%, respectively, and the reliability index and the failure probability determined by Monte Carlo method are 0.677 and 24.9%, respectively. However, for the FOSM method, the reliability index and failure probability are –0.025 and 51.0%, respectively. For both plane failure and wedge failure, the difference between the presented method and the Monte Carlo method is very small, but the failure probability of plane failure determined by FOSM method is larger than that of the other two methods. The presented method can provide a useful tool to evaluate the failure probability of rock slope.

Experimental study of the fragmentation characteristics of brittle rocks by the effect of a freefall round hammer

The dynamic fragmentation of brittle rocks (slate, granite, marble and limestone) under low-velocity impact was investigated using freefall round hammer experiments. A three-parameter generalized extreme value distribution was used to characterize the fragment sizes, and the finest particles were neglected. A

Determining the Critical Slip Surface of Three-Dimensional Soil Slopes from the Stress Fields Solved Using the Finite Element Method

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An empirical approach for evaluation of the potential of debris flow occurrence in mountainous areas

log10 transformation of fragment size was adopted to overcome the problem that the interval of adjacent fragments size increases as the fragment size grows. The results reveal that the frequency distributions and num-based cumulative frequency distributions based on number have a certain change law with variations in impact energy and hammer size; the frequency distribution curve became narrower, and the cumulative frequency distribution curve moved toward the left as the impact energy increased, and the hammer size decreased. Marble was most easily broken followed by granite, limestone and slate, which was proved by scanning electron microscope images of the fracture surfaces of the four rocks. Because fragmentation is a stochastic process, the equivalent diameters of the fragments always had a more obvious regularity than the major and minor axes in the histograms. Therefore, the mean value of the equivalent diameter was used as the experimental average fragment size. Comparing the experimental results with the theoretical results of average fragment sizes that were predicted by four normalized models, it was determined that Levy and Molinari’s model and Zhou et al.’s model better forecasted the fragment sizes.

Dam-break flood risk assessment and mitigation measures for the Hongshiyan landslide-dammed lake triggered by the 2014 Ludian earthquake

Cracks in rock mass have always posed a big threat on the durability of fractured rocks in shear zone. Cracking of rock mass in shear zone is a random process, highly variable and influenced by many factors. Cracks in fractured rocks can be repaired by injection of epoxy resin in order to bond the crack and restore its structural integrity. Epoxy resins are used to repairing the shear zone at the Jinping Hydropower Station. An improved polymer grouting material is adopted and the polymerization process is determined. The polymer grouting materials is consisted of resin (component A) and hardener (component B). Polarizing microscopy (PM) tests and mechanical experiments are adopted to evaluate the filling situation of epoxy resin in rock and the mechanical properties of epoxy-repaired rock, respectively. Experimental test results show that, the cracks and pores are filled by epoxy resin, and also the crack surface are boned. The mechanical properties of epoxy-repaired rock are improved by the polymer grouting and the permeability coefficient is decreased.

Two-dimensional stability analysis of a soil slope using the finite element method and the limit equilibrium principle

The slope stability problem is an important issue for the safety of human beings and structures. The stability analysis of the three-dimensional (3D) slope is essential to prevent landslides, but the most important and difficult problem is how to determine the 3D critical slip surface with the minimum factor of safety in earth slopes. Basing on the slope stress field with the finite element method, a stability analysis method is proposed to determine the critical slip surface and the corresponding safety factor of 3D soil slopes. Spherical and ellipsoidal slip surfaces are considered through the analysis. The moment equilibrium is used to compute the safety factor combined with the Mohr-Coulomb criteria and the limit equilibrium principle. Some assumptions are introduced to reduce the search range of center points and the radius of spheres or ellipsoids. The proposed method is validated by a classical 3D benchmark soil slope. Simulated results indicate that the safety factor of the benchmark slope is 2.14 using the spherical slip surface and 2.19 using the ellipsoidal slip surface, which is close to the results of previous methods. The simulated results indicate that the proposed method can be used for the stability analysis of a 3D soil slope.