Risk Assessment Of Rain-induced Unstable Slope In Danjia

As early as in the early 1950 s,China noticed the importance of disaster prevention and reduction,and began to study the mechanism and prevention of landslides.With the improvement of landslide hazard theory and control technology,the system of group measurement and mass prevention is gradually improved,but there are still many unstable slopes with a tendency to develop into landslides,which threaten personal safety and property loss.Because the instability of unstable slope is characterized by high uncertainty,it is a difficult problem to study its risk assessment.Therefore,it is of great significance to study the impact scale of human risk and economic risk from the perspective of the unstable slope itself and its inducing factors.Western Sichuan mountain gorge area is the key geological disaster prevention area in Sichuan Province.In recent years,the western Sichuan area has been affected by extreme climatic conditions,seismic activities and human engineering activities,and the number of unstable slopes has increased sharply.Rainfall is the most common natural inducement factor for instability of unstable slopes,among which short-term and high-intensity rainfall is the most common type.Therefore,it is of certain practical significance to carry out risk assessment research on unstable slopes under such rainfall conditions.Taking Danjia unstable slope as an example,this paper summarized and established a unique risk assessment system based on the theories and methods of landslide hazard risk assessment from domestic and overseas,and combined with the factors of the slope itself.The analysis contents included three parts: risk,vulnerability and risk estimation,and the ideas had certain reference significance for the risk assessment of similar slopes.The evaluation results can provide reference for the management and planning of this hidden danger point.Based on the results of the 2005 Vancouver International Conference,the risk estimation model is divided into two parts: human casualty risk and economic loss risk.Two numerical methods,ABAQUS and MASSFLOW,were used to simulate the instability process of Danjia unstable slope,and the output results were combined with mathematical statistics to conduct quantitative analysis of slope risks.The specific results are as follows:(1)Summarize the basic characteristics of the slope and analyze the deformation characteristics of the slope through field investigation data and survey data.The strength reduction method based on ABAQUS is used to reduce soil parameters to calculate the stability of slopes under two working conditions.The seepage field,displacement field,stress field and plastic zone of slopes are analyzed in combination with the seepage theory of unsaturated soil,and the curve of dependent variables such as pore pressure and displacement over time is output.Finally,the stability coefficients of Danjia unstable slope under natural conditions and rainstorm conditions are 1.15 and 1.025,respectively.The two conditions are defined as stable state and understable state according to the standard table of landslide stability classification.At the same time,the probability of landslide occurrence is calculated by conditional probability statistics method.It is considered that the probability of occurrence of Danjia unstable slope under natural condition and rainfall condition is 0.35 and 0.475 respectively.(2)The slip surface results of ABAQUS simulation of two working conditions were used as reference for the source determination of the sliding body in MASSFLOW simulation,and the threat range under two working conditions was determined according to the output velocity and accumulation thickness.The range of potential hazards to Danjia’s unstable slopes is then divided into three zones.(3)According to the characteristics of Danjia unstable slope,a unique risk assessment system is constructed.Among them,the slope stability,instability probability and threat range are used to analyze the risk,and the population vulnerability probability value of high-speed landslide is obtained by combining the population vulnerability formula with the survey data.Then the comprehensive vulnerability probability value of each zone is obtained according to the vulnerability evaluation formula of the landslide action intensity and the vulnerability of the disaster bearing body itself.Finally,the economic risk values of Danjia unstable slope under natural conditions and rainstorm conditions are 57,000 yuan and 7,746,500 yuan respectively,and the population risk values are 1 people/year and 44people/year,according to the calculation formula of individual landslide disaster risk value.This paper takes Danjia unstable slope as an example to establish a unique risk assessment system combined with its own factors.The thought of this analysis has certain reference significance for the risk assessment of similar slopes,and the evaluation results provide reference basis for the management and planning of this hidden danger point.