DDA Analysis On Creep Deformation Of Slope Triggered By Reservoir Impoundment

In recent years,the hydropower construction of China has obtained rapid development,a large number of high dams such as Jinping I,Xiaowan,Xiluodu,Dagangshan,Laxiwa,have been built and put into use.However,the reservoir impoundment has broken the original balance state of the rock mass in the reservoir area,making the geological environment and hydrologic conditions in the reservoir area unprecedented changes.After the reservoir impoundment,the bank slopes of these reservoirs all deformed with varying degrees and different types,and the deformation continues to grow with time,showing a strong time-dependent feature.The bank slope deformation caused by the uplift of the reservoir water level is becoming more and more prominent.The research on the triggering factor of the deformation and the mechanism of time-dependent deformation can provide an important basis for the long-term stability evaluation and the reinforcement of the bank slope.It can also be of great significance to ensure the normal operation of the hydropower project and maintain the social stability.The discontinuous deformation analysis(DDA)method has special advantages in simulating large deformation of discontinuous medium such as rock mass.Therefore,the DDA method is used as the main analytical tool to explain the deformation triggering factor and time-dependent deformation behavior of bank slope.In view of application demands,this paper improves the contact search algorithm and the method to determine the strength parameters of DDA.The analysis method of seepage-stress coupling effect and nonlinear creep of fractured rock mass have also been studied.Based on the results of the regression analysis of monitoring data,two practical projects are simulated and analyzed,and their deformation mechanism and failure modes are revealed.The specific contents of this article include:(1)The improvement of DDA's contact search algorithm.A contact search method based on angular bisector is presented in this paper.Based on the existing contact search method,the contact judgement is further made according to the location relation between the angle bisector of the entry angle and the invaded edge.The algorithm proposed in this paper improves the accuracy of the judgment in extreme cases.(2)Improvement of the method to determine the strength parameters of DDA.The random strength model of the rock mass is introduced to the DDA method,and the random strength is generated for each joint in the rock mass.Based on the random intensity of each joint,DDA simulation is carried out,so that the strength parameter is closer to the actual situation of rock mass,and the calculation and analysis results are more accurate and real.(3)Study on the seepage-stress coupling of jointed rock mass with DDA method.Based on the hydraulic characteristics of single fracture,a hydraulic model for seepage analysis of fractured rock mass is established by using discrete fissure network.The result of seepage analysis is applied to the element of DDA in the form of surface load,and the coupling relationship between "stress-opening-seepage" is established.Based on the principle of minimum potential energy,the general equilibrium equation of DDA considering the seepage load is derived The validity of the method is verified by comparison with the experimental results.(4)Study on the creep property of jointed rock mass with DDA method.The main form of slope and mountain deformation is "creeping and loosening".As one of the inherent mechanical properties of rock mass,creep is the phenomenon that the deformation of rock mass increases with time under the action of long term loads.The study on the creep characteristics of rock mass has great significance to reveal the mechanism of time-dependent deformation of rock mass.Aiming at the characteristics of rock creep,this paper introduces a function reflecting the overall stress state to improve the existing creep model,and the improved model could well reflect the linear and nonlinear creep characteristics of rock mass.In order to introduce the improved creep model into the DDA method,a recursive formula for creep strain increment is constructed,and the DDA sub matrix of block creep and contact creep is deduced respectively.Then the DDA equilibrium equation considering creep deformation is established.The corresponding numerical program is also developed.The validity of the program is verified by the creep test curve of rock mass at different stress levels.(5)The DDA simulation of a slope's toppling creep deformation has been carried out.Toppling deforamtion is one of the main instability types of layered rock slope.This paper takes the slope of a hydropower station as the research object,and establishes the DDA model based on the 3#ridge of the slope.Based on the monitoring data and regression analysis results of the bank slope,taking full account of the coupling characteristics of water and rock and the creep characteristics of the joint,the DDA simulation has been carried out.The form,the volume and the process of the deformation has been analyzed.(6)The DDA simulation of valley deformation of the Xiluodu arch dam has been carried out.With the rapid development of hydropower construction,a number of high arch dams have been built.In the short term after water storage,the valleys of these arch dams are all deformed in varying degrees,and the deformation has a tendency to increase continuously.This paper takes the valley of the Xiluodu arch dam as the research object,and makes a DDA simulation of the changes in the hydrogeological conditions on the two sides of the river valley.The change of the seepage field in the bank slope before and after the impoundment and its influence on the stress state of the bank slope are analyzed.The trigger factor of the deformation and the mechanism of time-dependent deformation have also been studied.