Study On Bearing Characteristics Of Different Lining Structures Of Circular Hydraulic Tunnel

Hydraulic tunnels play an important role in regional water transfer,hydropower generation,diversion,flood discharge,etc.Because of the internal water pressure,the lining structure mostly adopts multi-layer,composite,and prestressed lining.At present,there is a lack of practical calculation theory and bearing characteristics research of circular hydraulic tunnels.In this paper,the internal force,deformation,and bearing characteristics of circular hydraulic tunnel lining structure are theoretically deduced and analyzed by combining analytical solution derivation with numerical simulation,and the parameter influence analysis is carried out for actual case projects.The main research contents and conclusion of this paper are as follows:(1)By establishing the internal force calculation model of a single-layer lining hydraulic tunnel,and considering different water delivery pressures and water level heights,the internal force calculation formula of lining is derived.Using this formula,the influence law of water level and pressure on the internal force and distribution of tunnel lining is studied.In addition,two typical hydraulic tunnel projects are analyzed,and the changing law of lining internal force is obtained.(2)A simplified mechanical model of the composite double-layer lining structure(type 1)of a hydraulic tunnel is proposed.Considering the influence of the transition layer and the combined force of the inner and outer lining,the formulas for calculating stress,deformation,and internal force of the lining structure are derived by using elastic theory.The correctness of the analytical solution is verified by finite element analysis,and the influence of the thickness of the transition layer and lining material on the internal force and deformation of the lining structure is analyzed.(3)A simplified analysis model of a new composite lining structure(type 2)of "steel lining-SCC-segment" for hydraulic tunnels under the action of uniformly distributed internal water pressure is established.The segment,bolt,and joint gasket of the shield assembled lining are regarded as stress springs,and the formula for calculating the equivalent elastic modulus of the whole structure when the joint of the lining is partially tensioned and partially compressed is given.Based on the load structure method and the thick-walled cylinder theory,a calculation method for solving the stress and coordinated deformation of lining structures in each layer is proposed.The rationality of the calculation method is verified by finite element analysis of an engineering example,and then the influence of the thickness and material parameters of each layer lining structure on the stress and deformation of the structure is explored.(4)To reveal the bearing characteristics of the grouting prestressed lining structure,a stress analysis model considering grouting pressure is established,and the stress and deformation of the structure are calculated.The mechanism of prestressed grouting to improve the bearing capacity of the lining structure is revealed by comparing whether grouting prestress is applied or not.Based on the analysis of a three-dimensional numerical model based on engineering examples,the stress and deformation laws of tunnel structures in different stages of construction and operation are studied.Compared with the analytical solution,the correctness of the theoretical method is verified.Finally,the influence law of grouting prestress on the deformation,stress,and bearing capacity of the lining structure is analyzed by using this calculation method.