Study On Mechanism Of Rockfall Rainfall Initiation In Granite Residual Slope Based On Continuous-Discontinuous Coupling Method

With the great progress of poverty alleviation in China in recent years,the planning and construction of railways and highways in complex mountainous areas are also in full swing.In this process,the threat of falling stones distributed on various slopes along the line to human engineering activities has attracted more and more attention.This dissertation focuses on the rockfall problem in the coastal areas of South China,taking into account the climate and the characteristics of the surface rock and soil mass,in the dissertation,the granite residual soil slope and rockfall distributed on the slope in South China were selected as the research object.In view of the particularity of the coupled model,the research object is divided into two parts:residual soil slope and rockfall.Firstly,the rainfall infiltration characteristics of the slope foundation are studied based on the finite element method,Then,based on the rainfall results of the continuous model and the calibrated discrete domain parameters,the coupling calculation model is established after placing the rockfall.Based on FLAC^3D,considering the characteristics of regional meteorological conditions,this paper focuses on the impact of rainfall conditions and slope gradient on rockfall initiation,set up 30°?40°?50°slope to conduct the saturated and unsaturated seepage analysis,which is carried out under the condition of rainstorm and severe rainstorm.Considering that granite residual soil has the identity of cohesion reduction which is different from other soils,the softening effect correction module is written in FISH language on the basis of previous laboratory tests,the advantage of saturated-unsaturated seepage calculation based on FLAC^3Dis fully developed.The results of displacement field before and after adding the module are compared,and the necessity of adding the module and the validity of the correction are confirmed.The coupled computation of continuous-discrete elements requires the accuracy of the meso-parameters in the discrete domain,in this dissertation,the iterative method is used to carry out numerical experiments on the samples which are generated by modifying the grading parameters based on the limited computer performance,so as to carry out the macro and Meso parameter calibration,compared with the parameters and Stress–strain curve obtained from laboratory test,this method avoided the tedious and non-standard work of‘test parameters',and the calibration result is reliable.In this dissertation,five common rockfall models,such as flat body,cuboid body,rectangular plate body,cylinder body and near sphere body,are established.Based on the continuum-discrete element theory,a coupled calculation model is established,in which the effect of rainfall on the discrete domain is applied to the discrete domain particles in the form of equivalent force,the relationship between the start-up form and start-up time of rockfall and the shape of rockfall and slope gradient was discussed.The results show that the start-up form of rockfall is closely related to its burial mode,and with the increasement of slope,the start-up time of rockfall on the slope is greatly delayed.Based on the above research results,the relationship between rockfall initiation and rockfall shape and slope gradient is obtained,which can provide reference for rockfall prevention and Control Engineering.