Research on the stability analysis and design of soil tunnel surrounding rock

The paper first analyzes the failure mechanism and mode of tunnel according to model experiments and mechanical calculation and then discusses the deficiency of taking the limit value of displacement around the tunnel and the size of the plastic zone of surrounding rock as the criterion of stability. So the writers put forward the idea that the safety factor of surrounding rock calculated through strength reduction FEM(finit element method) should be regarded as the criterion of stability,which has strict mechanical basis and unified standard and would not be influenced by other factors. The paper also studies the safety factors of tunnel surrounding rock (safety factors of shear and tension failure) and lining and some methods of designing and calculating tunnels. At last,the writers take the loess tunnel for instance and show the design and calculation results of two-lane railway tunnel.

Frost heaving force considering synchronous damage to tunnel lining and surrounding rocks under freeze—thaw cycles

In areas with seasonal freezing,when the tunnel lining concrete is saturated with water infiltrating the interior,the lining and the surrounding rocks will simultaneously freeze.However,the current calculation of the frost heaving force fails to consider the synchronous damage to the lining and surrounding rocks under freeze-thaw cycles.Therefore,as per the elastic calculation model of the frost heaving force and model of steady-state heat transfer of circular tunnels,this study introduces the frost heaving rate of lining and surrounding rocks.First,the analytical solution of frost heaving force is obtained for simultaneous frost heaving of lining and surrounding rocks under any steady-state temperature field.Then,based on the fracture theory and meso-damage mechanics,the damage variables of lining and surrounding rocks under freeze-thaw cycles are extracted,representing their elastic modulus and porosity.Finally,the formula of frost heaving force for synchronous damage to the lining and surrounding rocks at any steady-state temperature field is obtained.The calculation results demonstrate that the lower the temperature inside the lining,the greater the frost heaving force.With the increasing number of freeze-thaw cycles,frost heaving force tends to gradually increase initially,reaching a peak value at 85 freeze-thaw cycles,decreasing to 80%of the peak value at 140 cycles before reaching a constant value.The lining participates in frost heaving,increasing the frost heaving force.The initial increase rate of frost heaving force is 15.7%.Changing the fitting coefficients s1 and s2 of the lining and surrounding rocks can effectively control the magnitude of the frost heaving force in the tunnels.

New methods of safety evaluation for rock/soil mass surrounding tunnel under earthquake

The objective of this work is to obtain the seismic safety coefficient and fracture surface and proceed with the seismic safety evaluation for the rock mass or soil mass surrounding a tunnel,and the limitation of evaluating seismic stability is considered using the pseudo-static strength reduction.By using the finite element software ANSYS and the strength reduction method,new methods of seismic safety evaluation for the rock mass or soil mass surrounding a tunnel are put forward,such as the dynamic finite element static shear strength reduction method and dynamic finite element shear strength reduction method.In order to prove the feasibility of the proposed methods,the results of numerical examples are compared with that of the pseudo-static strength reduction method.The results show that 1) the two methods are both feasible,and the plastic zone first appears near the bottom corners; 2) the safety factor of new method Ⅱ is smaller than that of new method I but generally,and the difference is very small.Therefore,in order to ensure the safety of the structure,two new methods are proposed to evaluate the seismic stability of the rock mass or soil mass surrounding a tunnel.A theoretical basis is provided for the seismic stability of the rock mass or soil mass and the lining surrounding a tunnel and also provided for the engineering application.

Excavation influence of triangular-distribution tunnels for wind pavilion group of a metro station

For the Guanshui Road Station tunnel project of Guiyang Metro Line 2,the wind pavilion group was moved out of the main tunnel to reduce the number of openings in the main tunnel,and the wind pavilion group was excavated in a triangular configuration at the entrance of the main tunnel.Based on the finite element software ABAQUS,a three-dimensional model is established to study the influence of different triangular-distribution tunnels excavation schemes on the surface settlement and tunnel stability.The objective of this study is to reveal the change rules of surface settlement,deformation and force in the support structures and the surrounding rock and identify the best excavation scheme for this tunnel configuration.Results show that to control the surface settlement and the deformation of the support structures,the optimal excavation sequence involves excavating the upper fresh air exhaust tunnel before the lower running tunnel.To control the stress of the support structures,the optimal excavation involves excavating the lower running tunnel before the upper fresh air exhaust tunnel.In this project,the most reasonable excavation sequence of the tunnel is from top to bottom.The most reasonable thickness of tunnel penetration is 5 m.

Analytical modeling of the direct tunneling current through high-k gate stacks for long-channel cylindrical surrounding-gate MOSFETs

An analytical direct tunneling gate current model for cylindrical surrounding gate（CSG） MOSFETs with high-k gate stacks is developed. It is found that the direct tunneling gate current is a strong function of the gate＇s oxide thickness, but that it is less affected by the change in channel radius. It is also revealed that when the thickness of the equivalent oxide is constant, the thinner the first layer, the smaller the direct tunneling gate current.Moreover, it can be seen that the dielectric with a higher dielectric constant shows a lower tunneling current than expected. The accuracy of the analytical model is verified by the good agreement of its results with those obtained by the three-dimensional numerical device simulator ISE.