| The South to North Water Transfer Project is taken as the engineering background of this thesis and the excavation disturbed zone and damage zone,deformation characteristics, stress evolution law and rock mechanical behaviors in surrounding rock of tunnel by TBM driving are studied.The Major works of this thesis are summarized as follows:(1) Base on the comprehensive investigation of the complicated existing environment of the South to North Water Transfer Project,the formation lithology,geological structure, distribution of in-situ stress field and complicated construction scheme are studied,and it is indicated that the key influence factors on stability of surrounding rock of tunnel are deeply buried,big length,complicated distribution of in-situ stress field and developing of joint fissures.(2) The uniaxial compression test of slate,the triaxial compression test of slate and the loading and unloading triaxial tests of different surrounding rock in varied unloading rate have been finished,and the Hoek-Brown empirical strength criterion is used to fit the rock mechanics parameters of slate.The mechanical properties and failure characteristics of slate indicate that the slate presents as brittle failure and has post-peak residual.The failure strength of slate is related to the unloading rate,the unloading rate is faster,the strength is higher,and the failure confining pressure is less.(3) The computing program is compiled to reach the theoretical solutions of surrounding rock deformation,stress and plastic zone after circular tunnel excavation.The numerical simulation method is applied to analyze the deformation,principal stress, variation law of principal stress orientation and size of plastic zone of surrounding rock in the traditional excavation.The work theory of TBM driving is that the incremental launching action makes the cutter head embedded in rock,and the rotation of cutter head makes the rock excavated.So in the numerical simulation,three direction velocities are used to simulate the TBM driving process,the axial velocity is to simulate the incremental launching action of the cutter head,the tangential and radial velocity are used to simulate the cutting action of the cutter head,and the plastic zone is assumed to be excavated.In the same conditions,the three results of theoretical solutions,traditional excavation and TBM driving are compared and show that the displacements value in TBM driving are about 65% of theoretical solution and traditional excavation method,and the plastic zone is only 58% of the theoretical solution,70%of the traditional excavation method.However the general deformation tendency is close for the three methods.(4) On the basis of the results of the loading and unloading triaxial tests in varied unloading rate,Hoek-Brown empirical strength criterion is used to fit the slate mechanical parameters including cohesion and friction angle.The FLAC3D program which contains the loading and unloading criterion is adopted to analyze the excavation disturbed zone and stability in surrounding rock of tunnel in varied TBM driving speed.The results show that the driving speed is faster,the excavation disturbed zone in surrounding rock is smaller,and the stability of surrounding rock is better;the deformations of surrounding rock are uniformly distributed after excavation;in the radial direction of tunnel,three zones are obviously shown for the displacement and stress variation:strongly varied zone,weakly varied zone and stable zone;along the tunnel radial direction,the maximum principal stress gradually vary from uniaxial to biaxial and triaxial,and the second deviatoric stress invariant forms a closed stress concentration zone which is called "stress dike" and is great helpful to rock breaking;the excavation disturbed zone of tunnel varies with TBM driving speed,when the speed increases 100%,the excavation disturbed zone decreases 64%,from 1.1 meter to 0.4 meter.(5) Considering the rock post-yield damage,a new constitutive model based on the CWFS brittle model is proposed in this thesis and is implanted to FLAC3D program by debugging dll in VC++.Based on the results of triaxial compression tests,this constitutive model is verified through parameter back analyzing by optimization algorithm such as neural network and genetic algorithm.The results show that the model can reflect the elastic characteristic,post-yield characteristic,brittle failure and post-failure residual strength characteristic of slate.Based on this model,the surrounding rock damage characteristic of TBM driving of the South to North Water Transfer Project are studied and also compared with the results by Mohr-Coulomb constitutive model.And the conclusion is drawn that the constitutive model in this thesis can better reflect the damage rule of the surrounding rock in TBM driving,that damage develops along the weak zone.(6) The process of rock damage by cutting head in TBM driving is studied in condition of varied buried depth,joint inclination and spacing with the UDEC2D code.The conclusions are drawn that the formation of rock fracture goes through three stages, generation,development and transfixion;two main fractures are generated in the damage process,one parallels to the direction of joint,the other intersects to the joint and form a closed fracture.The relationship of cutting head penetration value and the number of cutting head is also evaluated.On the basis of joint statistical law of the South to North Water Transfer Project,it is assumed that joint distribution accords with the normal distribution,and the relative joint generation program is compiled to UDEC.Using random joint distribution model,the excavation damage characteristic in the surrounding rock of tunnel are studied.The results show that part block falling occurs around the tunnel and integral uplift occurs at the bottom of tunnel.The surrounding rock failure of tunnel presents as tension failure around the tunnel and converts to shear failure along the radial direction of tunnel.
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