Mechanical Study And Application On Tunnel With The Intermediate Principal Stress

The stress analysis of tunnel and underground engineering is an important field of civil engineering research.The excavation model of tunnel engineering can be simplified to the plane strain circular axisymmetric model as the hole expansion.The hole expansion theory can be applied to the deep research of tunnel engineering.The theory of cavity expansion can solve many complicated geotechnical problems through simple and practical methods,and is widely used in the practical engineering problems,such as the results interpretation of soil site in situ test,tunnel and underground excavation analysis,and so on.Neglecting the elastic deformation of the plastic deformation zone,the relationship between the pore pressure and the pore deformation is relatively simplified.It is particularly important for the soil with relatively large internal friction angle,dilation angle and relatively small elastic stiffness.Different strength criteria have great influence on the theoretical solution of reaming problem.Considering the intermediate principal stress,the strength potential of material can be exerted to a greater degree.take the intermediate principal stress into account,the theoretical solution of reaming problem and its application in hydraulic tunnel are studied in this paper.The main contents are as follows:(1)Based on the unified strength theory and the no phase associated flow rule,and considering the influence of the softening characteristics and the dilation characteristics.The theoretical solution of the plastic zone radius and the ultimate reaming pressure in the process of dilatation is derived,according to the small deformation in plastic zone and the large deformation in plastic zone.Based on the theoretical solution of the small deformation in the plastic zone and the elastic region,the effect of the elastic strain in the plastic zone is considered,but the analytical solution neglects the effect of the deformation on the position of the middle point of the material,and is only suitable for the small reaming problem.For the theoretical solution based on the large deformation in plastic zone,the prediction limit of reaming pressure is more accurate.The unified solution provides theoretical basis for the solution of cylindrical cavity problem,and has reference value for engineering design.(2)A simplified excavation model which is similar to the expansion of cylindrical holes is adopted.based on the double shear unified strength theory and the three shear strength criterion,cosidering seepage,dilation,softening and elastic modulus of plastic zone,the unified solution of the plastic zone displacement of hydraulic tunnel containing five factors is derived.When the parameters are taken from different values,the displacement solution can be degenerated into a series of solutions.The value of the parameters can be reasonably selected according to the concrete engineering example,and it has extensive applicability.The correctness of the theoretical solution is further verified by comparing with the existing literature,and the difference between the two principal stress parameters under the strength theory is analyzed.(3)The ABAQUS finite element software is used to simulate the cone static penetration test,and the deformation maps of the soil in 4 different stages of the sinking process are given,and the stress curves and displacement curves under the two paths of the penetration process along the radial direction and the depth direction are also given.This paper also analyzes the influence of shear expansion,cohesion and internal friction Angle on the stress and displacement.