Fu-gang Xu

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%.

Geotechnical characteristics and stability analysis of rock-soil aggregate slope at the Gushui Hydropower Station, southwest China.

Two important features of the high slopes at Gushui Hydropower Station are layered accumulations (rock-soil aggregate) and multilevel toppling failures of plate rock masses; the Gendakan slope is selected for case study in this paper. Geological processes of the layered accumulation of rock and soil particles are carried out by the movement of water flow; the main reasons for the toppling failure of plate rock masses are the increasing weight of the upper rock-soil aggregate and mountain erosion by river water. Indoor triaxial compression test results show that, the cohesion and friction angle of the rock-soil aggregate decreased with the increasing water content; the cohesion and the friction angle for natural rock-soil aggregate are 57.7 kPa and 31.3° and 26.1 kPa and 29.1° for saturated rock-soil aggregate, respectively. The deformation and failure mechanism of the rock-soil aggregate slope is a progressive process, and local landslides will occur step by step. Three-dimensional limit equilibrium analysis results show that the minimum safety factor of Gendakan slope is 0.953 when the rock-soil aggregate is saturated, and small scale of landslide will happen at the lower slope.

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.

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

Debris flows can occur relatively suddenly and quickly in mountainous areas, resulting in major structural damage and loss of life. The establishment of a model to evaluate the occurrence probability of debris flows in mountainous areas is therefore of great value. The influence factors of debris flows are very complex; they can basically be divided into background factors and triggering factors. Background factors include the mechanical characteristics of geo-materials, topography and landscape, and soil vegetation; and triggering factors include hydrological and rainfall conditions, and human activities. By assessing the dynamic characteristics of debris flows in mountainous areas, some important influence factors are selected here for analysis of their impacts on the occurrence probability of debris flow. A mathematical model for evaluation of the occurrence probability of debris flows is presented and combined with probability analysis. Matlab software is used for the numerical implementation of the forecasting model, and the influences of rainfall, lithology and terrain conditions on the occurrence probability of debris flows are analyzed. Finally, the presented model is applied to forecast the occurrence probability of debris flows in the mountainous area around Qingping Town; the simulation results show that many loose landslide deposits and heavy rainfall are the key factors likely to trigger debris flows in this region.

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

ABSTRACT Landslide-dammed lake is a typical geological hazard induced by earthquakes in mountainous river areas that pose a great threat to human lives and property for reservoirs and downstream areas. In this paper, the 3 August 2014, Hongshiyan landslide-dammed lake induced by the Ludian earthquake (Mw 6.5) was taken as an example to study the dam-break risk and flood routing process. The fuzzy mathematics method was used to evaluate the risk level of the Hongshiyan landslide-dammed lake, and six main indicators were developed to classify its risk level. The assessment results indicated that the Hongshiyan landslide-dammed lake had an extremely high risk and very serious possible disaster consequences. Then, we analyzed the possible dam-break flood routing process by numerical simulation. The simulated results showed that a dam-break flood would pose a great threat to the downstream Tianhuaban Hydropower Station. Therefore, some effective artificial measures must be taken to control the scale of the disaster. The artificial measures included upstream interception, middle grooming, downstream emissions and subsequent treatments. Some emergency measures were implemented and prevented the failure of the landslide-dammed lake through 19:00, October 4 2014, and subsequent treatment even turned the potential harm into a benefit.

Experimental Research on the Dam-Break Mechanisms of the Jiadanwan Landslide Dam Triggered by the Wenchuan Earthquake in China

Dam breaks of landslide dams are always accompanied by large numbers of casualties, a large loss of property, and negative influences on the downstream ecology and environment. This study uses the Jiadanwan landslide dam, created by the Wenchuan earthquake, as a case study example. Several laboratory experiments are carried out to analyse the dam-break mechanism of the landslide dam. The different factors that impact the dam-break process include upstream flow, the boulder effect, dam size, and channel discharge. The development of the discharge channel and the failure of the landslide dam are monitored by digital video and still cameras. Experimental results show that the upstream inflow and the dam size are the main factors that impact the dam-break process. An excavated discharge channel, especially a trapezoidal discharge channel, has a positive effect on reducing peak flow. The depth of the discharge channel also has a significant impact on the dam-break process. The experimental results are significant for landslide dam management and flood disaster prevention and mitigation.

Effects of model parameters, topography, and scale on the mass movement processes of debris avalanches using the discrete element method

The mass movement process of a debris avalanche is a complex dynamic system and is influenced by topographic conditions, material composition, sliding-bed surface conditions and other factors. A discrete element method is used to simulate the mass movement process of debris avalanches and is validated by laboratory flume tests. Sensitivity analyses for the model parameters show that a low bond strength indicates that a small impact force can lead to slope failure. The friction coefficient has a little effect on the mass movement process. However, high particle stiffness and bond strength causes the sliding material to behave like a rigid block of rock; therefore low bond strength and particle stiffness are selected to simulate the laboratory flume tests. The velocity of the sliding material increases with the increasing slope of the flume. If the sliding material hits a barrier, the travel direction will change and energy dissipation will occur, resulting in the sudden decrease in velocity. With an increase in landslide volume, the model parameters particle stiffness and parallel bond strength should be increased to ensure the reasonableness of the simulated results. When the landslide volume is not large enough, the selection of those model parameters has no significant effect on the movement process. The proper selection of model parameters is very important for the reasonableness of the simulated results.

An Experimental Study on the Water-Induced Strength Reduction in Zigong Argillaceous Siltstone with Different Degree of Weathering

The water-softening property of soft rocks is a key problem in geotechnical engineering. A typical red-bed soft rock (the Zigong argillaceous siltstones) with different weathering degree is selected as an example to study the water-softening property and the influence of degree of weathering. A series of mechanical and microstructure tests are carried out to analyze the weathering characteristics and mechanism of the Zigong argillaceous siltstones. The results of mechanical experiments reveal that the water content and the weathering degree of rock specimens both have a weakening effect on the compressive and shear strengths. According to the results of present microstructure tests, the mechanical properties of the Zigong argillaceous siltstones are closely correlated with their physical properties, including internal microstructure and material composition for highly weathered rocks or moderately weathered rocks (in both natural and saturation conditions). Finally, experimental results indicate that the changes of microstructure and internal materials are two main factors that influence rock strength parameters after contacting with water and that these properties reflect the rock weathering degree. In a word, when red-bed soft rocks are encountered in geotechnical engineering, special attention should be paid to presence of water.

Exponential smoothing method based on wavelet transform for slope displacement prediction

It has important significance in engineering to analyze rock slopes evolution rule and forecast its development trend based on the safety monitoring displacement data. The actual slope monitoring sequence is non-stationary time series containing a number of errors, therefore, firstly discrete stationary wavelet transform (DSWT) are used to denoising for monitoring data, then the reconstruction series are transformed into a stationary sequence by first-order difference, finally exponential smoothing method is used to prediction for the stationary differential sequence. The combination forecasting model is applied to high slope displacement prediction on the left bank of Jinping I Hydropower Station, the calculation results show that the combined model have higher forecast accuracy compared with other prediction methods, most of the relative errors of the prediction results are less than 5%, meeting engineering prediction requirements.

A Slope Stability Analysis Method Combined with Limit Equilibrium and Finite Element Simulation

This paper presents a slope stability analysis method combined with the limit equilibrium and finite element simulation. Based on the simulated stress of a slope, the safety factory of one element can computed with Mohr-Coulomb criterion, and introduces the Dijkstra algorithm of graph theory to search the dangerous slide surface combined with limit equilibrium method. For an examine slope, the simulated results of safety factor and location of dangerous sliding surface is close to the strength reduction method. Sensitivity analysis results show that, the safety factor of slope is decreased with the increasing height and inclination of slope, but decreased with the decreasing cohesion and friction angle.