Application Of Discontinuous Deformation Method (DDA) In Analysis Of Toppling Rock Slope Under River Erosion

The toppling of anti-dip layered rock slope is a typical mode of rock slope failure.Because this kind of deformation phenomenon is very common in hydraulic engineering and highway engineering,it has been paid more and more attention by the engineering community.The theoretical research on toppling rock slopes was mainly based on the analysis method of limit equilibrium proposed by Goodman and Bray(abbreviated as G-B method).In the later period,people used centrifuge to study the process of toppling deformation,but all of the models are relatively simple and can not realistically simulate the actual shape and mechanical state of the rock mass.so,the conclusions are only a preliminary understanding of toppling deformation,and they are difficult to play a good role in the engineering project.The numerical simulation method is a new research method developed in recent years,because the establishment of model and the setting of parameter are simple,and the conclusions are straightforward,so it is widely used in practical engineering analysis.In view of the well-developed joints in the toppling slope,the rock mass are cut into blocks,and this type of slope is often accompanied by large deformation problems such as collapse and dumping.Therefore,the discontinuous deformation analysis method(DDA)is selected in the paper for the research of deformation process and the deformation mechanism to this type of slope.Based on the research status of toppling deformation at home and abroad,this paper selects two areas which has more toppling slopes in Zhen'an County,Shangluo City,Shaanxi Province and Heihe Reservoir District,Xi'an City,Shaanxi Province,and selects two typical bending dumps as the research object,and uses discontinuous deformation analysis method(DDA)to research the toppling deformation phenomenon under river erosion.By analyzing the data of slope displacement field and stress field,the slope deformation process and deformation mechanism of this kind of slope are obtained.The main research contents and conclusions are as follows:(1)In view of the inability of DDA to calculate different operating conditions,this paper uses the method of extracting model slopes data?joint data and extracting unit stress field data to solve this problem,and applies this method into calculating toppling slope under the effect of river erosion.(2)According to the actual observation and geological analysis on the site,the geological causes of the bending toppling deformation of the Zhen'an County is the joint action of tectonic action,surface rainfall infiltration,and river erosion;the main factors of bending toppling in the Heihe reservoir area are the river erosion,rock mechanical properties,and layer thickness.(3)Using Batton's roughness-based structural plane strength calculation method,this paper analyzes the geometric parameters of Bartton's standard curve,and proposes a calculation method of the structural surface roughness based on the Batton's reference curve geometric parameters,and applies this method into calculating the strength parameters of the structural plane in this paper.The results of structural plane strength parameters proved that the proposed method has certain accuracy and can be applied in the project.(4)Using DDA method to study the deformation process and deformation mechanism of the bending toppling slope in thin rock mass and medium-thick layer rock mass.It is concluded that the deformation process of the thin rock mass slope is divided into five stages: the stress recombination stage,the slope top crack deformation stage,the initial toppling deformation stage,the dump-slip deformation stage,and the destruction stage.Because of the stress concentration of river erosion,the normal stress of the structural plane of the slope foot rock mass is increased,which increases the shear strength of the structural plane.The upper rock mass is accompanied by stress release and the deflection of the principal stress direction is the occurrence of dumping deformation;The deformation process of the medium-thick layer rock mass slope is divided into five stages: the stress recombination stage,the initial bending stage,the bending mutation stage,the bending stabilization stage,and the destruction stage.The shear stress concentration near the bending zone and the deflection of the main stress direction above the bending zone is the cause of the rock bending.