Study On Stability Of Tunnel Surrounding Rock Based On Strain Softening Of Rock Mass

China is a mountainous country,with the road construction gradually into the mountains, mountain road tunnels began to appear and gradually to a longer, larger direction,in the tunnel design and construction process of correctly judging the stability of surrounding rock is the key. For rock, especially in soft rock or hard rock under high stress, most of which are with strain softening and plastic dilatancy characteristics. At present, there are more and more researches on the theory and numerical simulation of strain softening model of rock mass, but the research on strain softening of tunnel surrounding rock is still lacking.This paper takes the Muzhailing tunnel in Gansu Province as the project, based on the theory of tunnel mechanics and strain softening,by using Flac3D to establish numerical model for simulation,and combined with field monitoring measurement for comparative analysis, the stability of tunnel surrounding rock based on strain softening is studied. The specific research contents and results are summarized as follows:?The application of Mohr-Coulomb strength criterion, the axial plastic shear strain?1p as the strain softening parameters, and it is expressed as a function of friction angle? and cohesion of c, the conversion as a function of axial strain, in order to obtain expressions for the deformation modulus and stress-strain relationship of rock after peak.Compared with the experimental data of Z.Fang and J.P.Harrison, the results show that the post peak curve of the rock is well fitted.? Combined with example,and discussed the different deformation stages of post peak softening parameters namely cohesion c and internal friction angle ?, softening dilatancy angle ? of stress-strain curves of rock after peak through orthogonal simulation, that the cohesion deterioration was the most important factor affecting the stability of tunnel surrounding rock; the internal friction angle of inferior the influence of the influence of dilatancy angle; deterioration of the minimum. Increasing the residual strength of broken rock can effectively control the deformation and failure of tunnel.?According to Muzhailing Tunnel Project in Gansu Province, strain softening of this article using the Flac3D software model with conventional Mohr-Coulomb model to simulation of tunnel excavation, the area of plastic zone of strain softening model is larger, and the vault of the settlement and horizontal convergence value are larger than the Mohr-Coulomb model. Therefore, considering the influence of strain softening, it is possible to make the appropriate amount of deformation reserve and improve the supporting strength in the construction process, which has a good guiding role in engineering.?The amount of dome settlement and the horizontal convergence value of the on-site monitoring and measurement are about 70% ?80% of the deformation calculated by numerical simulation. The results are relatively close, indicating that the selected research methods and the results of the overall more reliable. According to the results of the deformation of the surrounding rock, it is suggested that the secondary lining should be carried out after 20 days of excavation of the surface of the face (from the tunnel face 40 ?50m).