Dynamic Analysis Of Transient Unloading Of Deep-buried Rock Mass Based On Elasto-plastic Cellular Automaton

Due to underground rock mass frequently exposed to in situ stress,Tunnel Boring Machine(TBM)or Drill Blasting(DB)excavation may cause the damage of surrounding rock mass and then physical characteristics of rock mass are affected.Rock mass excavation presents a process of unloading,thus influence of further investigation with regard to various excavation methods on the physical characteristics of rock mass can provide theoretical basis and technical guideline for practical engineering.Due to the heterogeneity and complexity of rock mass,it is difficult to obtain analytical solution for the process of transient unloading of rock mass,while numerical simulation is a powerful tool for analyzing dynamic response triggered by rock mass excavation.The existing numerical methods are based on the overall idea for conducting dynamic analysis,while it is time-consuming for the investigation of large geological body.Based on cellular automaton software of failure process of rock mass(CASRock),which means Elasto-Plastic Cellular Automaton,EPCA,this paper utilizes local principle of the cellular automaton,establishes its dynamic updating rules and develops dynamic computational part discretized on both spatial and temporal scales by using the cellular automaton technique and the Newmark time integration scheme,respectively.Validation of EPCA is tested based on analytical solution and other numerical results,and then it is employed to analyze dynamic response of transient unloading of deep-buried rock mass.The main work and research results are as follows:(1)The agreement of propagation of elastic wave between EPCA and analytical solution validates the feasibility of dynamic analysis with EPCA.Time histories regarding displacement are same as analytical results,while counterparts with regard to stress oscillate so that errors between them appear.Based on the error distribution obtained by EPCA,HHT method and TDG scheme,it reveals that the computational accuracy of EPCA is good.The agreement of elasto-plastic analysis based on EPCA,ABAQUS and BEM validates the non-linear dynamic simulation for EPCA.(2)Implementing Laplace transform for governing equation and constitutive equation,frequency-domain solutions for stress,displacement,velocity and acceleration can be obtained.Based on the Den Iseger numerical inverse transform,corresponding time-domain results can be obtained.Comparing error between analytical solution and the Den Iseger numerical inverse results,it reveals that the Den Iseger numerical inverse method keeps high precision and stability.Moreover,time histories obtained by the Den Iseger approach are same as the characteristics of method,it further indicates high precision and stability of the Den Iseger method.(3)Results for transient excavation between EPCA and the Den Iseger method are in good agreement.Findings are as follows: the bigger in situ stress is,the more remarkable vibration rock mass around tunnel is.Pronounced difference occurs due to various unloading paths,the bigger unloading rate and excavation radius are,the more remarkable vibration is.With the increase of lateral pressure coefficient,failure of two sidewalls around tunnel moves to the roof and floor.The smaller heterogeneity coefficient is,the severer failure around the tunnel.As the coefficient increases,symmetrical failure around the tunnel appears.The existence of joint deteriorates the failure at the edge of tunnel.