Study On Treatment Measures Of External Water Pressure On Lining Of Hydraulic Tunnel In Water-rich Area

Long-buried hydraulic tunnel is the key subject in the construction of national water network,which has the characteristics of large buried depth and large hole diameter.The method of using external water pressure reduction coefficient in the Code for Design of Hydraulic Tunnel(SL279-2016)to determine that external water pressure is directly used for lining design has restricted the development of hydraulic tunnels in deep-buried water-rich areas.To solve this problem,taking the typical water-rich tunnel sections of"Yin Chao Ji Liao"project 2~#and 5~#as examples,this paper makes an in-depth analysis and research on the change of groundwater seepage field in the initial,excavation,mixing and operation periods,the influence of external water pressure reduction coefficient of permanent lining and tunnel seepage flow by means of theoretical analysis,field monitoring and numerical simulation.And carried out the simulation study on the optimization scheme of the tunnel blocking and drainage structure.Finally,considering the reduction coefficient of external water pressure of the tunnel lining and the tunnel seepage flow,the new measures to deal with the high external water pressure in the water-rich section were put forward.The main research contents and results are as follows:1.Based on the seepage theory,the theoretical calculation formulas of external water pressure reduction coefficient of composite lining and tunnel seepage flow are deduced,which are verified by Midas GTS NX software,and the influence law of grouting circle change on external water pressure reduction coefficient of lining and tunnel seepage flow is summarized.2.Through the combination of field monitoring and numerical simulation,the evolution law of seepage field in tunnel excavation period,mixing period and operation period is studied,and the evolution law of groundwater seepage field in typical tunnel sections during tunnel excavation and construction period and the influence of tunnel construction on groundwater are revealed.3.Midas GTS NX software is used to study and reveal the evolution law of seepage field and the change of external water pressure reduction coefficient of lining under the existing tunnel design scheme of the project.The influence of drainage holes and grouting rings on the reduction coefficient of external water pressure of lining and the seepage flow of tunnel is studied,and the law that the reduction coefficient of external water pressure of lining and seepage flow change with the drainage measures is summarized.4.In order to solve the risk of lining bias damage caused by external water pressure,a new treatment measure for high external water pressure in the water-rich section with a water-collecting layer between the surrounding rock and the lining is put forward,and the influence of the thickness and permeability coefficient of the water-collecting layer on external water pressure and seepage flow is revealed.