Analysis Of Seepage Tunnel With High External Water Pressure And Study On Stress Of Composite Lining

In the western provinces and regions of my country,the topography is rich and diverse,and the geological structure is complex and changeable.While building water delivery tunnels to achieve cross-regional water transfer,the tunnels cross large faults,the rock formations are complex,and there are local water-rich zones,which are inevitably affected by highlands.During the construction and operation of the tunnel,the effects of stress and high external water pressure seriously threatened the stability of the structure.Therefore,it is very important to investigate changes in infiltration and external water pressure during tunnel construction and operation;analyze the characteristics of the surrounding rock and composite lining and propose load shedding measures to ensure the safety of the project.This paper studies the Liupanshan 1# tunnel,uses a simplified model to derive the seepage flow of the tunnel,analyzes the seepage flow in the secondary lining during the construction period of the tunnel and the internal seepage flow of the segment during the operation period with the height of the water head,the grouting circle,the initial support,the Variation law of permeability and thickness of lining;based on the theory of fluid-solid coupling,a numerical model of the permeability field of the 1# tunnel rupture zone was established using ABAQUS finite element software.The influence of head height,grouting circle,initial support,permeability and lining thickness on the external water pressure of the lining and pipe section is analyzed.Influence and obtain the relationship curve between seepage flow rate and external water pressure;five special sections are selected to establish a numerical model to analyze the stress field of the surrounding rock and tunnel structure,Analyzed whether the surrounding rock and each part of the tunnel force meets the design requirements;based on the pea gravel triaxial test simulation,analyzed the backfill pea gravel grouting thickness change of the load reduction effect.The main research conclusions are as follows:(1)The results of the study on the tunnel seepage flow show that with the continuous increase of the water head height,the seepage flow in the tunnel gradually increases,showing a linear relationship.The method of applying grout to strengthen the surrounding rocks can effectively reduce the penetration of the tunnel and in the process of increasing the thickness of the grout circle,the seepage flow tends to be stable and hardly changes;reduce the initial support and transfer coefficient of the lining,and increase the thickness of the lining.Reducing the seepage flow in the tunnel has obvious help.During construction,increase the thickness of the initial support and grout ring,or reduce the hydraulic conductivity of the initial support and grouting circle can reduce the external water pressure on the tunnel and reduce the internal seepage flow of the tunnel.(2)Using ABAQUS software to build a three-dimensional model of tunnel and analyze the external water pressure of tunnel,it can be concluded that: the seepage flow in lining and segment is inversely proportional to the external water pressure,and the water pressure decreases with the increase of the seepage flow.Grouting circle of permeability coefficient is less than 1 x 10-10 m/s,web of pressure bear completely by the grouting circle,lining segment web of pressure and close to zero,grouting circle thickness is more than 7 m,lining and segment web of pressure change is not obvious,the comprehensive analysis of grouting circle thickness 5 m,1 x 10 to 9 m/s permeability coefficient when the tunnel seepage flow to meet the standard,lining,segment force meets the requirements,the best effect.(3)Five special sections are selected for stress and deformation analysis.The results show that the deformation of surrounding rock varies greatly due to the difference in buried depth.The maximum deformation of the surrounding rock at a depth of 300 meters is 4.5cm;The maximum deformation of the surrounding rock increases to 13.9cm at a depth of 1080 meters.Due to the influence of the section shape,the lining and the initial support arch foot position are subject to greater force.Great care should be taken in the structure to prevent danger.The upper and lower parts of the arch are the concentrated force area.The increase in the buried depth of the tunnel leads to a gradually increase in the maximum stress.Due to ground stress change again during the excavation of the tunnel,when the tunnel is buried When the depth is greater than 500 meters,the stress value of the tube segment increases slightly,and it is basically in a stable state.(4)Analysis of the load reduction effect of the backfilled bean gravel grouting shows that the anti-deformation ability of the bean gravel is inversely proportional to its own porosity.Before being compacted,it can effectively offset the deformation of the surrounding rock or lining and protect the pipe from damage.The backfill grouting has obvious effect on the load reduction of the tunnel,and the load reduction effect of the backfill layer is the best when the backfill layer is 15～30cm.