Study On Strain Softening Mechanism And Stability Control Of Deep Roadway Surrounding Rock

Under the influence of high temperature and high pressure and excavation disturbance,there are some non-linear mechanical behaviors of the deep rock mass,which is characterized by elastic-plastic coupling,strain softening and plastic failure.For deep underground excavation engineering,the surrounding rock near the excavation surface was usually in a post-peak strain softening state.However it still has a certain carrying capacity.Therefore,its mechanical properties including own-bearing capacity,deformation character and stability character were important for deep rock excavation project.It is necessary to carry out relevant research,in order to reveal its related mechanical behavior,and thus carry out theoretical calculations and numerical simulation work.In this paper,based on the three-axis cyclic loading-unloading test data,a new strain softening model considering the elastic-plastic coupling effect was developed,and a new true-triaxial rock strength criteria considering intrinsic material characteristics was proposed.Besides,the new model was took into the elasto-plastic analytical solution for circular cavity problem.At last,an elastic-plastic coupling strain softening model was developed in the FLAC.The main contents of the work are as follows:Firstly,the rock strength criteria was studied considering the characteristics of the three-direction stress bearing situation of the deep rock mass.Based on the analysis of the true triaxial test results,the deficiencies of the existing 2D strength criteria were discussed.The impaction of the three principal stresses on the rock strength criteria was analyzed:(a)rock strength increased with the minimum principal stress,however,its increasing amplitude gradually decreased and trends to be zero;(b)the ratio between generalized compression and extension strength first increase then reduced,and finally trends to be one with the increasing minimum principal stress.So,the envelope of strength criterion on deviatoric plane varies from approximate triangle to circular;(c)during the process of intermediate principal stress increasing from minimum principal stress to maximum principal stress,rock strength firstly increased and then decreased.Based on the influence induced by the three principal on the rock strength and the advantages of the true triaxial criterion on the meridian surface,the LWW,LMN and LYMH functions are introduced to discrube the influence of the intermediate principal stress on the rock strength.The true triaxial strength criterion of EWW,EMN and EYMH which accord with the three characteristics of rock strength is deduced.Secondly,the strain softening model was studied considering the elastoplastic coupling characteristics of deep rock mass and the influence of high confining pressure.It is suggested that the mechanical properties of the surrounding rock should consider the influence of the current stress state and the plastic strain history.Based on the analysis of the existing three-axis cyclic loading-unloading test data,the variation of the strength parameters,deformation parameters and the dilatancy angle of the surrounding rock during the softening stage of the surrounding rock are studied under the influence of confining pressure and plastic strain.The results show that,Cohesion,internal friction angle,elastic modulus and dilatancy angle could be described by constructing a two-dimensional function on the surface composed of the confining pressure-equivalent plastic shear strain,which has a higher fitting accuracy with the experimental results.Then it was applied into the FLAC numerical program.Thirdly,the circular cavity elasto-plastic analytical solution base on the rock strain softening model.The strength and deformation parameters of the rock are shown strain softening and confining pressure dependence effect.For this nonlinear effect,the rock parameters decreases with the plastic strain and improves with the confining pressure.The elastic zone and the softening zone are divided into n-1 rings,and each ring is divided into three parts: the rupture zone,the softening zone and the elastic zone.The material properties are assumed the same,and then the elasto-plastic coupling analysis method of circular tunnel excavation considering strain softening is proposed.Using M-C criterion and H-B criterion,the method of solving the circular tunnel stress and deformation is obtained.The method proposed in this paper is proved to has good accuracy by comparison with the results of the elastic rock mass,conventional strain softening rock mass and elasto-plastic coupling strain-softening(EPCSS)rock masses published by predecessors.Fourthly,Secondary development of the FLAC numerical analysis program: UDM is the secondary development program interfaceprovided by FLAC 3D.Through the Visual Studio which is a software development platform,the constitutive model builtin FLAC with C + + language was compiled into dynamic linkage file”.dll”.The proposed constitutive model is embedded into FLAC 3D for numerical simulation.The correctness of the model was verified by simulating the triaxial test and the actual test data.Finally,by simulating the excavation of the circular tunnel,the comparison with the MC model and the SS model showed that the EPCSS model better reflects the confining pressure of the surrounding rock.Destruction and deformation characteristics due to plastic accumulation.In the study of underground engineering excavation,the influence of different constitutive models on the deformation and plastic zone of surrounding rock was analyzed.The numerical simulation shows that the constitutive model constructed can more accurately reflect the mechanical behavior of the surrounding rock after fracture,and has good convergence and stability.Finally,The elastic-plastic coupled strain-softening model is applied to the stability analysis of a deep soft rock roadway,and the displacement field and stress field distribution of roadway roof,two and bottom slab are studied by numerical simulation with the step excavation process method using the proposed model.It is showed that the model can reflect the plastic deterioration deformation characteristics of roadway.Based on the calculation results,the scheme of the composite support structure for controlling the plastic deformation of surrounding rock and improving the stress state of the surrounding rock is proposed,which achieve a prefered results.