Research On Calculation Method Of Rock Pressure Of Tunnel In Soil-thick/Rock-thin Stratum

In recent years, more and more highway tunnels and underground railway traffic have been constructed, resulting in complex stratum engineers may encounter. However, most theoretical studies and analysis methods is based on homogeneous layers, not comprehensively taking the difference of physical and mechanical parameters between the composite stratum into consideration, which is difficult to meet the demands of the construction of complex composite stratum, among of which tunnel in soil-thick/rock –thin stratum is one of the representatives. Due to the great difference of properties between rock and soil and lack of mature theoretical system and relevant reference specifications, research on characteristics of surrounding rock stress and displacement for the tunnel in soil-thick/rock-thin stratum is becoming an urgent problem to be solved.In the paper, with finite element analysis software, numerical simulation method has been used to do research on the characteristics of surrounding rock stress and displacement and make quantitative analysis of the vertical stress on the surface of soil and rock for the tunnel in soil-thick/rock-thin stratum. With the orthogonal test, the main influencing factors of the vertical stress on the surface of soil and rock can be determined, and then the relevant multivariant nonlinear regression model is established by the least square method. What’s more, through a combination of the vertical stress on the surface of soil and rock and classic calculation theories of rock pressure, the discussion on method of rock pressure for the tunnel in soil-thick/rock-thin stratum is carried out. The main results of this thesis are presented as follows:(1) For the tunnel in soil-thick/rock-thin stratum(V1-V1), along the vault path, the maximum principal stress direction and values are unique, and the distance from tunnel vault to the surface of soil and rock has effects on the change of maximum principal stress values and the maximum value of maximum principal stress. Besides, the crown settlements and horizontal displacements have a great difference between the tunnel in soil-thick/rock-thin stratum and the tunnel in the same grade rock, while the displacements of the arch bottom are approximately the same.(2) For the tunnel in soil-thick/rock-thin stratum(V1-V1), the vertical stress on the surface of soil and rock is greatly affected by soil thickness, the distance from tunnel vault to the surface of soil and rock, and the internal friction angle and cohesion of rock, what’s more, the relevant multivariant nonlinear regression model is established between them.(3) By using the vertical stress on the interface of soil and rock instead of gravels to establish equivalent model and applying the Terzaghi’s theory, Xiejiaxiao’s theory and Bill Bauman’s theory, the method of rock pressure calculation of the tunnel in soil-thick/rock-thin stratum can be discussed. According to the practical project, the theoretical calculation value is compared with measured value from the distribution along tunnel radial direction.