The Discontinuous Deformation And Displacement(DDD)Method And Its Engineering Application

This thesis focuses on developing the discontinuous deformation and displacement(DDD)method to model the nonlinear deformation and failure behaviors of jointed rock masses based on the continuum mechanics,statistical damage theory and contact theory.By hybridizing the classical RFPA and DDA methods,the proposed DDD method can inherit the advantages of both and is able to provide a complete and unified description for not only the entire rock deformation process(including crack initiation and propagation),but also the rock body movement(including translation,rotation and interaction).In the DDD method,by deducing a unified global equilibrium equation,the continuous and discontinuous problems can be solved jointly,and the mechanical behaviors of continuous regions and discontinuous structural planes can be simulated simultaneously by using a unified computational model;the automatic transformation of rock materials from continuous medium to discontinuous medium can be realized by constructing the specific fracture sequence to communicate continuous medium with discontinuous medium;by establishing a unified analytical framework,the cracking process of rocks in small deformation stage and the movement and contact process in large displacement stage can be fully captured,and the whole process simulation of rock failure and instability can be realized.Furthermore,to improve the deformation results and refine the stress distributions within blocks,finite elements are introduced into model blocks.Because of the embedded finite elements,the stress and strain fields of a single block can be calculated more precisely.In the traditional DDA method,the stress and strain of a single block is constant regardless of the shape of the block.Obviously,such treatment is not appropriate for blocks with sharp angles.Although it can be improved by reducing the average block size of block systems,the computational cost will increase significantly.Simultaneously,the ability of an intact block to fracture is determined by these finite elements,i.e.,the rock blocks containing a number of finite elements are deformable and may split into smaller pieces if the strength criteria are satisfied continuously.The grid lines of damaged elements represent newly formed joints,and sliding and opening may occur along the new joints,i.e.,mechanical interaction is allowed between adjacent blocks.Additionally,the correctness and validity of the proposed method are verified through a series of benchmark tests.The stress field,bending deformation,dynamic sliding,and strength characteristics and crack propagation are further analyzed to validate the effectiveness of the code.The simulated results are found to be consistent with the analytical solutions,previous studies and experimental observations.In conclusion,for the proposed coupled RFPA/DDA method,the analysis region can be modelled using a unified formulation,allowing rock-like quasi-brittle materials to transform from continuum into discontinuum materials when the failure criteria are triggered in the model.Although many challenges remain,the proposed method proves to be effective and reliable to model the nonlinear mechanical behaviors of jointed rock masses and has shown its particular advantages over the conventional numerical methods.