Study On Vertical Deformation Mechanism Of Cracked Lining In Rich-water Mountain Tunnel

With the continuous development of China’s engineering construction,the number of built and under construction tunnels is increasing.Deep buried long mountain tunnels have become one of the main focuses.Tunnel construction in high-pressure and water-rich mountainous areas is the top priority.From the past engineering examples,with the increase of service time,this underground structure located in complex engineering geology and hydrogeology will appear different degrees of structural diseases.In this paper,based on the project of Liaozi tunnel in Chengkou,following the waterproof and drainage principle of’mainly blocking and limited discharge’,using the method of combining theoretical analysis and numerical simulation,the distribution law and deformation law of water pressure outside the lining structure with joints are studied,and the waterproof and drainage design is deeply analyzed.The relationship between the drainage system pressure,drainage volume and the safety factor of the lining structure is studied.The research results are as follows:（1）The basic theory of groundwater seepage is expounded,and the two functions of seepage water pressure in porous media and the coupling principle of seepage and stress are briefly introduced.Based on single fracture seepage theory,the theoretical solution of equivalent seepage parameters of lining structure with cracks is derived.This paper introduces the method of fluid-solid coupling analysis in FLAC^3D,and the analysis steps of fluid-solid coupling.（2）The stress redistribution of lining structure occurs under the condition of cracks,and the permeability coefficient of lining structure changes,which has a certain impact on the water pressure distribution and deformation of lining structure.In addition,based on numerical simulation,the external water pressure distribution and lining structure deformation of single crack under different water level,different permeability coefficient and different crack position are studied.It is concluded that the groundwater level has the greatest influence on the lining structure,followed by the change of crack position and permeability coefficient.（3）The influence of symmetrical combined cracks and asymmetrical combined cracks on the lateral water pressure distribution and structural stress of the lining is studied by numerical simulation.Among them,in the case of symmetrical combined cracks,the lateral water pressure and deformation of the lining structure are roughly symmetrical with respect to the axial direction of the tunnel.In the case of asymmetric combined cracks,the external water pressure and structural stress of lining structure show great differences in the area near the crack and the area far from the crack.The cracks at the inverted arch of the tunnel are the most unfavorable to the stress of the tunnel structure,and the most unfavorable combination is the combination of‘the right side of the inverted arch+the bottom of the inverted arch’.（4）Based on the waterproof and drainage principle of“water plugging and limited drainage”,FLAC^3Dnumerical simulation software was used to study the distribution of water pressure outside the lining and the internal force distribution of the lining structure by changing the different pressure relief values of the drainage pipe.It is concluded that when the pressure relief value increases,the water pressure borne by the lining structure increases,the internal force of the lining structure at all positions increases,the drainage volume decreases,and the safety factor of the lining structure decreases.When the discharge pressure is 0.4 MPa,the drainage volume is 1.022 m³/m/d and the safety factor is 11.96.