Experimental And Theoretical Study On Seepage Characteristics Of Waterproof And Drainage System Of Composite Lining

Waterproof and drainage system is an important part of composite lining tunnel.The conventional estimation methods of groundwater inflow and external water pressure on lining often neglect some factors associated with the fracture of surround rock and waterproofing and drainage system,which may lead to a gap between the actual engineering observations and estimations.Considering all the components of waterproof and drainage system,the experimental and theoretical methods are carried out to research on the permeability characteristics of the waterproof and drainage system.A three-dimensional waterproof and drainage seepage model is put forward,and the analytical solutions of groundwater inflow and external water pressure on lining are derived.Secondly,a characterization formula of equivalent permeability coefficient of composite lining and a formula of relationship between drainage rate and external water pressure reduction coefficient are proposed.Then,an optimal design method of tunnel waterproof and drainage system is proposed,which provides theoretical method for the optimal design of lining structure and waterproof and drainage system.The main research contents and results are as follows:(1)According to the similarity criterion,the similar materials of surrounding rock and model experimental device are developed,and the tunnel seepage model test including surrounding rock,initial lining,secondary lining,circular drainage pipe,geotextile and waterproof membrane is designed.According to the model test,the trend of the waterproof and drainage system on groundwater inflow and external water pressure is explored,and the permeability characteristics of"surrounding rock-waterproof and drainage system"are revealed.(2)According to the model test results,a three-dimensional waterproof and drainage seepage model(WDSee model)is proposed.Then,the analytical solutions of groundwater inflow and external water pressure on composite lining are derived,considering all the components of waterproof and drainage system.The derived analytical solutions are verified using model test and numerical method.Secondly,the influencing factors of groundwater inflow and external water pressure are analyzed,and the effects of the distance between two adjacent circular drainage pipes,the layer number of geotextile and its permeability coefficient,and the waterproof performance of waterproof membrane on groundwater inflow and water pressure are obtained.(3)Based on the WDSee model,the FWDSee model of waterproof and drainage seepage in fractured rock mass is further proposed,the semi-analytical solution of gronndwater inflow and external water pressure of fractured rock mass tunnel with horseshoe section is derived,and the influence of fracture width and orientation is analyzed Finally,the analytical solution is applied to an engineering example to test its accuracy.(4)A characterization method of equivalent permeability characteristics on composite lining considering circular drainage pipe,geotextile and waterproof membrane is proposed,which provides a simplified calculation method of equivalent permeability coefficient for theoretical and numerical analysis of tunnel groundwater inflow and external water pressure.(5)In order to balance the relationship between the limited groundwater inflow and the external water pressure on composite lining,the relationship between tunnel drainage rate(ratio of groundwater inflow of composite lining to that of unlined tunnel)and the reduction coefficient of external water pressure on lining is established.Taking the minimum external water pressure loaded on the initial lining and secondary lining as the optimization objective,the optimization method of tunnel waterproof and drainage system and grouting zone is proposed,which reachs the requirements of limited discharge and allowable bearing capacity of lining.Finally,based on the Baoshiling Tunnel in Anhui province,the groundwater inflow and the external water pressure on composiye lining are estiamted and analyzed,and the optimal parameter range of the waterproof and drainage system and grouting zone are given.Combined with the on-site initial lining and grouting construction technology,the optimal parameters are selected to treat the grouting sections of the tunnel.The results show that the amount of groundwater inflow decreases from12.53m~3/d/m to 2.41m~3/d/m after grouting,decreased by 80.8%.The external water pressure on initial lining and secondary lining decreased by 68.6%and 96.5%respectively.The groundwater table rises from less than-20m to-15m after grouting.The resules indicate the rationality and reliability of the proposed optimization method,which can be applyied in the optimization design in practical tunnel engineering.