Effects Of Stress Release Rate On Stability Of Soft Surrounding Rock In Highway Tunnels

In the construction process of the tunnel, the excavation boundary stress releasesgradually as the tunnel advances forward. The stress release rate of surrounding rock isdeeply affected by the factors such as the tunnel engineering geological conditions,structural dimension, construction method, supporting time, and so on. Particularly, how toselect the stress release rate of soft or rheological rock is directly related to the design oftunnel support structure. Therefore, it needs further analysis, which helps the optimizationof whole tunnel structure.Firstly, the formation process of the surrounding rock pressure and its influencingfactors are analyzed which are based on existing theoretical research. And the surroundingrock pressure theories and the surrounding rock-support structure interaction principle arereviewed. And it provides a theoretical foundation for establishing numerical analysismodel and choosing working conditions.Secondly, the three-dimensional elasto-plastic analysis model of tunnel portal sectionin soft rock is established by finite difference program package FLAC^3D. On the basis ofthis model, the deformation of surrounding rock and the mechanical characteristics ofsupporting structure under different conditions of the stress release rates are analyzedemphatically. The results show that the stress in soft surrounding rock is smaller, and toensure the stability of the tunnel structure the initial stress release rate should not be toolarge.Finally, based on FLAC^3Dnumerical simulation program, the stability of surroundingrock under different combinations of the distance between invert and tunnel face+stressrelease rate of surrounding rock is investigated, and stress release rates of surroundingrock under different geological conditions are optimized. The calculation results show thatwhen the distance between invert and tunnel face is1.2D （D means excavation clearanceof single-hole tunnel） the primary lining and surrounding rock can both play their fullyroles. Stress release rate predominates in controlling crown settlement and invert heaving.But to hance convergence displacement, stress release rate and distance between the invertand tunnel face play the same role. As improvement of the surrounding rock grade,stresses in the surrounding rock will increase gradually. The achievements in this thesis can be valuable for selecting proper stress release rateof the surrounding rock in tunnel construction and the global optimization of supportsystem.