Stability Analysis For Surrounding Rockmass Based On CWFS Model

One of the purposes of rock mechanics analysis is to analyze the stability of surrounding rock of underground excavation,a great deal of research done with surrounding rock of underground excavation indicate that the cohesion-weakening and friction-strengthening(CWFS)model based on Mohr-Coulomb criterion can better predicate the rock deformation degree and scope than the traditional Mohr-Coulomb model which assumed that the cohesive and the frictional strength components are mobilized simultaneously.The main purpose of this paper is to use the CWFS model to analysis the stability of surrounding rockmass,to have a better understanding of the concepts of cohesion-weakening and friction-strengthening,So as to better guide the design and construction of underground excavation.First of all,this paper introduces the common theory of rock mass strength criterion,analysis the the damage process of geotechnical material in which that the cohesive and the frictional strength components are mobilized non-simultaneously,and introduces the CWFS model.Secondly,by using the FLAC3D,this paper uses the ideal elastic-plastic model,strain softening model,elastic brittle model and CWFS model to model the Mine-by circular test chamber the numerical simulation based on the theoretical analysis,and demonstrates the practicability of CWFS model by comparing the displacement,stress distribution and plastic zone of rockmasss;this paper studies the influence of various mechanics parameter by analyzing different mechanics parameters of the CWFS model,And introduce the concept of sluggish coefficient,The main conclusions include:(1)The traditional model assuming simultaneous mobilization of the cohesive and frictional strength cannot well predict the damage of the surrounding rockmass.(2)CWFS model can be represented with a bilinear envelope.In the damage process of rockmass,the cohesive strength original dominants the mobilized strength,and eventually the frictional gradually dominant the mobilized strength as the cohesion is consumed.(3)The horizontal and vertical displacement of the surrounding rock from CWFS results model's simulation significantly greater than other models.The stress field of CWFS model can more accurately response the feature that stress transfer and concentration to a deeper location when the damage zone form.(4)Compared with other traditional models,CWFS model can effectively predict the depth and range of failure zone,its result is more consistent with the measured date in situ.(5)The influence of different parameters on the CWFS model simulation results are different,in which the initial friction angle,peak friction angle,initial cohesive,the corresponding critical plastic strain of cohesive and friction strength(?_c~p and ?_f~p)have bigger influence on the CWFS model simulation results,and the residual cohesive and dilatation angle have a litter influence on it.(6)The depth and range of the failure zone is a function of the delay coefficient which is introduced in this paper.The delay coefficient is a function of plastic strain(?_f ~p and ?_c~p),and clearly considers the delay of frictional strength relative to cohesive strength during the brittle failure process.(7)The delay coefficient of rock is the critical factors in controlling the damage zone shape.To build a experience formula about the delay coefficient,can better predict the excavation failure zone and guide engineering project.Finally,this paper uses CWFS model to simulate the four diversion tunnel of the Jinping?Hydropower Station,and demonstrates the importance of excavation scheme to the stability of surrounding rock.