Description For The Nonlinear Characterisitc Of Tunnel Surrounding Rock Mass And Its Stability Analysis By Numerical Method

Tunnel is mainly built in the rock mass with some degree of stress and tectonic structure. Interpreting and mastering the basic characteristic of rock mass, and making the correct estimation of the surrounding rock mass stability, are not only related to the tunnel designing and construction, but also related to the whole tunneling engineering cost. The former linear describing criterion has some certain limitation, so it is important to study the nonlinear failure model for describing the rock mass strength, and the stability of rock mass under the nonlinear failure criterion, which has great engineering meanings.The former research materials are collected in the present paper, while the theoretical analysis method and numerical simulation method are adopted. The following studies are done, the nonlinear failure model of the tunnel surrounding rock mass, the obtaining method for its parameters, tunnel stability under the nonlinear failure criterion, stress deformation characteristic, determination method of the roof thickness, etc, which can give some guidance for the real practice.The transferring method of the parameters between Hoek-Brown criterion and Mohr-Coulomb criterion as well as the parameters between Barton-Bandis criterion and Mohr-Coulomb criterion are presented, and the effect of each nonlinear failure criterion parameter to the shear strength parameters are analyzed.According to the numerical calculation model based on the linear failure criterion and the nonlinear failure criterion, the numerical realization method of the Mohr-Coulomb linear criterion and Hoek-Brown nonlinear failure criterion are introduced. The tri-axial compressive tests are done by the both numerical method, the results validate the correctness of the numerical method based on the Hoek-Brown nonlinear failure criterion, and shows its advantages.The relationship between the parameters of Hoek-Brown criterion and Mohr-Coulomb criterion is founded by the theoretical method, the yielding approach index based on the Hoek-Brown criterion is deduced; Then a three dimensional calculation model is founded for the tunnel, the program for calculating the yielding approach index based on the Hoek-Brown criterion is compiled, and the validation of the program is done.The failure characteristic of the tunnel surrounding rock mass is described by the Hoek-Brown criterion, and the theoretical analysis is done for the stress and deformation situation of rock mass after tunnel excavation; Then the numerical calculation model is founded by FLAC3D, to study the displacement, shear strain distribution and plastic zone distribution, whose results are compared with the theoretical result.The stratified tunnel excavation model is founded by the FLAC3D, the deformation and failure situation of the stratified rock mass are analyzed, while the deformation and stress characteristic of rock mass based on the nonlinear failure criterion are presented.The calculation method for the safety thickness of the roof after excavation in tunnel is proposed based on the Hoek-Brown nonlinear failure criterion, the relationship of the span of tunnel and the safety roof thickness is analyzed as well as the stress deformation and failure situation of tunnel surrounding rock mass.The results of the studies are applied in the engineering practice, the comparisons are done for the settlement of tunnel roof in the real situation and the numerical situation, which shows that their differences are very small, and validates the correctness of the numerical calculation method. Finally, the results from the studies can give guidance for the real practice.