Research On Stress-strain Characteristics And Reinforcement Measures For Soft Rock Tunnel Under High Geo-stress And Seepage Action

During the construction of deep buried tunnels in the western region,the deformation problem of soft rock tunnels under high geo-stress is very prominent,and the effect of groundwater will not only change the stress field in the tunnel,but also make the mechanical properties of soft rock change,further aggravating the surrounding rock deformation.To address such problems,this thesis takes a tunnel project in the western region of China as the basis,and studies the stress-strain characteristics of high groundstress soft rock tunnel under the action of seepage by means of theoretical analysis,statistical analysis,numerical simulation,etc.,and on this basis,the reinforcement measures are studied.The main research results and conclusions are as follows:(1)Through statistical analysis and research of uniaxial and triaxial test data at home and abroad,the deformation characteristics of soft rocks under the action of water-force coupling are summarized and data fitting is carried out by using MATLAB to obtain the influence law of surrounding pressure on soft rock deformation parameters under two water-bearing states,and the concepts of instantaneous friction angle and instantaneous cohesion are introduced to obtain the change law of soft rock shear strength parameters and surrounding pressure under two water-bearing states.The results show that the shear strength parameters of soft rocks in the water-bearing state are not affected by the surrounding pressure.The results show that the soft rocks in the waterlogged state show ductile deformation characteristics,and the increase of the surrounding pressure will make the ductile characteristics more obvious.The modulus of elasticity of soft rocks in both water-bearing states increases with the increase of surrounding pressure,and the effect of water decreases the growth rate of modulus of elasticity with surrounding pressure,while Poisson’s ratio is less sensitive to the change of surrounding pressure.The friction angle of soft rocks in both water-bearing states decreases with the increase of surrounding pressure,and the cohesion increases with the increase of surrounding pressure.The cohesion of soft rocks in full water state is lower under the effect of zero surrounding pressure,and is more obviously affected by the surrounding pressure.The friction angle of soft rock in full water state is lower under the effect of zero surrounding pressure,and the magnitude of decrease with surrounding pressure is larger.(2)The numerical model is established by the law of change of parameters of surrounding pressure and soft rock,and the FISH language is written to control the changes of parameters of surrounding rock by radial stress,and the comparative analysis is carried out in four working conditions.The calculation results show that when the influence of surrounding pressure and water on the parameters of surrounding rock is considered simultaneously,the displacement generated by the tunnel excavation is the largest and the area of plastic zone is the largest.(3)Numerical simulations of the three-stage excavation of a soft rock tunnel with high ground stress were carried out by means of flow-solid coupling analysis to study the influence of different initial pore water pressure and different initial ground stress on the seepage field,displacement field,plastic zone and support forces.The results show that the maximum flow rate of groundwater occurs at the foot of the arch,and the increase of initial pore water pressure and initial ground stress will increase the tunnel water surge,surrounding rock deformation and deformation growth rate.The deformation at the bottom of the tunnel arch is the largest,and is most obviously affected by the growth of initial ground stress and initial pore water pressure.The largest extrusion deformation at the palm face is located at the lower step,which requires strengthening the support measures for the palm face and the tunnel arch bottom.(4)The influence law of grouting circle thickness and grouting circle permeability coefficient on seepage field,displacement field,plastic zone and support force situation was studied by numerical simulation.The results show that: a reasonable increase in the thickness of the grouting circle can reduce the amount of water in the tunnel excavation surface,reduce the surrounding rock deformation and plastic zone range.Grouting circle permeability coefficient reduction can reduce the tunnel excavation surface water,but will increase the surrounding rock deformation.