| When underground structure engineering traverses in water-rich environment,a series of engineering problems caused by the groundwater occur from time to time.Therefore,properly handling the relationship between underground structure and the groundwater is the most basic problem and prerequisite in the design and construction of underground structure engineering,and it is also one of the basic scientific problems in the field of underground structure engineering.The seepage characteristic of the surrounding rock of hydraulic tunnel and the external water pressure distribution of the lining structure are two important foundations for the design of hydraulic tunnel in waterrich environment.Seepage prevention and drainage are the keys to the success or failure of the construction of hydraulic tunnel.At present,the research on the distribution of groundwater seepage field in hydraulic tunnel is mostly based on circular tunnel engineering,and the anti-seepage and drainage measures of the surrounding rock of hydraulic tunnel mainly refer to road tunnel.Therefore,in this paper hydraulic tunnels with different cross-section shapes in water-rich areas are used as the research object,using a combination of theoretical analysis,numerical simulation and on-site monitoring to study the distribution of seepage field of hydraulic tunnel and the external water pressure acting on the tunnel lining.The main research contents and results are as follows:(1)Based on the theory of well-flow in infinite aquifer and the conformal mapping method of complex variable function,an analytical calculation method of tunnel seepage field distribution and seepage velocity considering the shape of the section is proposed;The analysis of the factors affecting the seepage characteristic of hydraulic tunnel in three aspects of tunnel section height width ratio,the groundwater and the characteristic of the surrounding rock shows that for a rectangular tunnel,the seepage velocity at the corner point is the largest,and the seepage velocity gradually decreases as the distance from the corner point;for a straight-walled round-arch tunnel,the seepage velocity at the foot of the wall is the largest,followed by the seepage velocity at the top-arch,the seepage velocity gradually decreases with the distance from the foot of the side-wall and reaches a low value in the middle of the side-wall and the bottom-plate.(2)Using the finite difference method,a three-dimensional numerical simulation of the seepage characteristic of hydraulic tunnel in water-rich environment was carried out,and the distribution law of the tunnel seepage field obtained by the numerical simulation was compared with the analytical calculation result,and the results are in good agreement.On this basis,numerical simulation is used to explore the seepage of surrounding rock and the force characteristic of the supporting structure under different external water pressures and internal water pressures under different external water pressure and different internal water pressure in straight-walled circular-arch tunnel.The results show that with the continuous advancement of excavation face of tunnel construction,the groundwater seeps into the cave,and the porewater pressure of the surrounding rock drops,a funnel-shaped water pressure distribution curve is formed around the tunnel due to the difference in water pressure.(3)Aiming at the pre-grouting technique before excavation used in hydraulic tunnel to reduce water inflow during construction,an analytical solution for water inflow of circular tunnel in semi-infinite aquifer is derived.Through the correlation analysis of the analytical solution,a simplified solution of the ratio of water inflow of ungrouted tunnel to water inflow of probe hole is obtained;at the same time,the correlation between the ratio of water inflow of grouting tunnel to water inflow of ungrouted tunnel(grouting anti-seepage effect)and hole sealing efficiency are analyzed.On this basis,the thickness of the grouting circle is determined according to the allowable drainage of hydraulic tunnel and sealing efficiency of on-site pre-grouting technology.(4)Based on the theory of well-flow in infinite-aquifer,theoretical derivation and analysis of the external water pressure distribution of lining structure of circular tunnel are carried out.The analysis results show that as the thickness of the grouting circle increases,the permeability coefficient of the grouting circle decreases,and the tunnel drainage volume increases,the external water pressure of lining structure decreases;when the drainage volume of the tunnel drainage system can be greater than the seepage flow through the grouting anti-seepage ring,the external water pressure value of lining structure can be reduced to a relatively small value.(5)Numerical experiments are used to simulate the external water pressure distribution under the conditions of the deterioration of the anti-seepage performance of lining structure in horseshoe-shaped tunnel and the failure of the drainage system.The simulation results show that when considering the anti-seepage of the lining,the influence of the deterioration of the lining on the external water pressure distribution is closely related to the degree of the deterioration of the lining,with the increase of the permeability coefficient of the lining,the external water pressure decreases.In the failure state of the drainage system,compared with the external water pressure in the normal state of the anti-seepage drainage,the external water pressure at the top of the vault increases significantly when the circular permeable blind pipe is clogged and fails to block;the external water pressure in the middle of the side wall increases greatly when the longitudinal drainage pipe fails to block;the external water pressure in the middle of the invert is increased greatly when the circular permeable blind pipe or the longitudinal drainage pipe is blocked and fails.(6)Taking the straight-wall round-arch diversion tunnel support project as the research background,on-site monitoring and data analysis were carried out.The results showed that the backfill grouting and consolidation grouting to block the groundwater passage reduced the water inflow of hydraulic tunnel and the external water pressure acting on the lining was reduced;When using drainage holes penetrating the consolidated grouting layer and the central drainage ditch under the bottom plate for drainage,the external water pressure of the lining is further reduced.The numerical simulation analysis results are basically consistent with the on-site monitoring results. |
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