Analytical Research On The Surrounding Rock Pressure And Deformation Induced By Excavation Of Soil Tunnels

The property, size and distribution of surrounding rock pressure provide valuable basis of tunnel support, structure design and construction project. It ensures the stability of surrounding rock by freeing some deformation, which allows adjustment of stress in the rock, reduces the thickness of lining at the same time. This paper studies the surrounding rock pressure and deformation for soil tunnels by analytical analysis and numerical simulation, and the following main research results are made:1) Considering the supporting pressure, physical and mechanical parameters of surrounding rock and geometric parameter of the tunnel, an analytical solution of stress and displacement of surrounding rock is derived based on the circular tunnel analysis model and stress function method. Along the vertical direction, radial stress of surrounding rock at the crown will appears the minimum value point, between this point and the roof of the tunnel are the major distribution region of release stress, namely the excavation disturbed zone. The disturbed boundary due to excavation at various supporting pressure are provided, which indicates that the disturbed zone is reduced with increasing of supporting pressure.2) Analytic function of surface settlement trough is derived on the basis of the analytical solution of surrounding rock displacement. With this function, regularities of inner surface supporting pressure of the tunnel, physical and mechanical parameters of surrounding rock and geometric parameter of the tunnel on surface center point and surface settlement trough range can be achieved. The analytical solution of plastic boundary that considers re-distribution influence of plastic stress is derived by combining the analytical solution of surrounding rock and Mohr-Coulomb strength criterion. The critical plastic support pressure is defined by the inner uniform support pressure When the plastic zone boundary is the excavation face, as well as the equation of critical plastic support pressure is derived. Effects of the inner surface supporting pressure of the tunnel, physical and mechanical parameters of surrounding rock and geometric parameter of the tunnel on the size and distribution of plastic zone are analyzed by applying the analytical solution of plastic zone. Moreover, the results are compared with the solution derived by Kastner.3) The numerical simulation results are compared with a test results of a stratum deformation mode conducted by our research group. The comparisons indicate that the numerical model based on stress path constitutive model agrees well with the regularity of model experiment. Therefore, a great number of simulation with various buried depth and excavation radius are established by using the stress path constitutive model. Analysis results indicate that when the ratio of tunnel buried depth measured from top of the arch to its radius beyond 7, the vertical displacement of the crown in steady state without support has nothing to do with buried depth, while it is related to tunnel radius and mechanical parameters of surrounding rock.4) With the help of elastic theory and numerical model, vertical displacement expression of the crown in steady state without support is obtained. Inflection point of elasto-plastic deformation is achieved by combination of analytical solution of surrounding rock and Mohr-Coulomb strength criterion, then the inflection point is modified by numerical result, thus the deformation-pressure relation of surrounding rock is achieved. It can be used for tunnel excavation scheme formulation and technical measures implementation to provide scientific support.