Study Of Dynamic Process Of Earthquake-induced Landslides Using Improved Discontinuous Deformation Analysis

Earthquake-induced landslides,especially the large-scale high-speed and long-runout landslides induced by earthquakes,are different from ordinary gravity-induced landslides.The catastrophic loss caused by earthquake-induced landslides is huge generally,and the dynamic mechanism of the landslide formation process is quite complicated,which has always been a hotspot in academic research.The instability mechanism and the low friction phenomenon during high-speed sliding process of the earthquake-induced landslides are more concerned.Scientific understanding of the dynamic mechanism is of great practical significance to the disaster prevention and control of the earthquake-induced landslides.In this thesis,the aim is to simulate the whole process of earthquake-induced landslide and analyze its instability and movement mechanism,the Discontinuous Deformation Analysis(DDA)method is used as a research tool.In view of some problems existing in the simulating process of earthquake-induced landslides: treatment of the dynamic boundary,simulation of the analysis model from continuous to discontinuous and introduction of the strength weakening constitutive.Some improvements have been made to the DDA method in order to achieve the numerical simulation of the whole dynamic process of earthquake-induced landslides including cracking,progressive failure,instability,initiation,high-speed sliding,and deposition.The dynamic response mechanism in the process of earthquake-induced landslide formation is analyzed.The research results in this thesis will provide a new idea for the study of the entire dynamic process of earthquake-induced landslides.The main research contents and achievements obtained in this work are as follows:(1)The theoretical basis of the numerical method(DDA)was introduced,including the derivation of potential energy of the system,the establishment of governing equations,and the handling of contacts.The input method of ground motion in DDA was improved.The viscous boundary and free field boundary were introduced into the DDA method,and the seismic wave was input as the nodal force,so that the improved DDA method could simulate the propagation of seismic wave in the rock body.Some numerical exampls were used to verify the improvement.(2)The joint parameter definition and determination in the original DDA is not suitable for the simulation of block systems with multiple joint parameters.So,based on the actual physical meaning of joints,a joint parameter definition and determination method determined by the contact blocks on both sides of the joint was proposed.The new definition and determination method of joint parameters can adapt to the fracture and movement process simulation of earthquake-induced landslide composed of multiple rock masses.The corresponding program was written and integrated into the original DDA program,and three sliding models of blocks and a landslide case were taken as examples to verify the applicability and effectiveness of the improved DDA method.(3)The multi-spring edge to edge contact model was introduced to improve the original DDA program,and the application of virtual joints was added.So that the problem of tensile failure of joints can be delt better,and the progressive failure of joints and the fracture of rock mass can be realized.Then the improvement can be used in the simulation of the cracking process of earthquake-induced landslides.The influence of the number of spring pairs applied on the edge-to-edge contact on the accuracy of the calculation result was discussed.In the simulation,11 pairs of spring pairs applied to an edge-to-edge contact can achieve sufficient accuracy.(4)The B-B model considering the attenuation of shear strength with roughness of the joints was introduced.In this model,the joint roughness will be gradually degraded with the relative shear displacement of the joint between the two contact blocks,so that the DDA can simulate the friction attenuation characteristics of the joint surface and sliding surface during the shearing process,and realize the simulation of low friction during the landslide sliding.This model was added to the DDA code,so that the roughness coefficient between joints can be updated in every time step with the relative sliding displacement between the contact blocks.The validity of the attenuation model was verified by comparing the simulation results with the relevant experimental results of a shear model with two blocks.A single-slider sliding model was simulated which slided along a inclined plane under the dynamic load,and the influences of the dynamic loading amplitude and loading time on the stability of the slider were discussed.(5)The above improvements are integrated into the DDA method.The Donghekou landslide induced by 5?12 Wenchuan earthquake in 2008 was took as an example,and the dynamic process of the Donghekou landslide was numerically simulated.The entire process of Donghekou landslide including cracking,progressive failure,instability and initiation,high-speed sliding and deposition was reproduced by the simulations,and the entire dynamic process of Donghekou landslide was obtained.Due to the introduction of the dynamic boundary,the mountain body has a significant amplification effect on the seismic wave,and the peak ground velocity(PGV)at the toe and the back part of the sliding body are obviously large,indicating that these places are prone to damage.A large tensile crack is formed at the trailing edge of the landslide,then the sliding surface at the front edge of the sliding mass is sheared through,and the whole landslide shows a tension-cracking and shearing sliding failure mode.At about the 15 th second of the action of the ground motion,the cracks in the slope began to rapidly expand,and several major crack propagation zones were formed.At about 23 th second,the sliding surface was completely penetrated and the landslide began to slide.The friction coefficient of the sliding surface decreased sharply during the period of formation of the sliding surface,and then the landslide body collapsed at high speed.The movement distance and the final deposition state of the Donghekou landslide simulated by the Improved DDA are in good agreement with the actual conditions of the local topography.