Study On The Characteristics Of The Retractable Secondary Lining Structure Of Hydraulic Tunnels

During the water conveyance operation of hydraulic pressure tunnels,the secondary lining structure of hydraulic tunnels is simultaneously subjected to surrounding rock pressure and high internal water pressure,and under the action of complex stresses with dominant and secondary alternating characteristics,the lining surface often appears along the axis of the tunnel.Tension cracks that develop towards and develop radially.The appearance of such cracks will cause the water in the tunnel to seep out and form a certain seepage water pressure,the secondary lining structure and the surrounding rock stress state will worsen,and the tunnel will enter a vicious circle of working conditions until the whole is destroyed.In this regard,the improvement and reinforcement of the surrounding rock and the reinforcement of the secondary lining are used to deal with this limitedly,but it is difficult to work in the case of high internal water pressure and weak surrounding rock.Therefore,on the basis of proposing a new type of circularly flexible tunnel lining structure,the paper adopts theoretical calculation,numerical simulation analysis and model test to improve the stress state,deformation and displacement characteristics of the flexible tunnel lining structure.The adaptability of geotechnical engineering environment and hydraulic conditions are analyzed and studied.The main research work completed and the main results obtained are as follows:(1)Based on the theory of thick-walled cylinder in elastic mechanics and Winkler elastic foundation beam theory,theoretical calculation formulas for internal force and displacement of traditional hydraulic tunnel lining structure and retractable lining structure were established by theoretical analysis,and actual hydraulic tunnel engineering was used.The design parameters have been calculated and verified respectively and compared and analyzed.The results show that the hoop stress of the retractable lining structure is significantly smaller than that of the traditional lining structure.(2)Based on the numerical model of typical hydraulic tunnel surrounding rock,lining and its ancillary structure,the stress state and deformation displacement of tunnel lining are calculated and analyzed by using ABAQUS tool.The distribution characteristics of stress and deformation displacement of traditional tunnel lining structure and scalable tunnel lining structure and surrounding rock are obtained and compared.The results are in good agreement with the theoretical analysis.At the same time,according to different surrounding rock pressures and water pressure values in the tunnel,the changes between the surrounding rock pressure and internal water pressure and the stress state and deformation displacement of the retractable tunnel lining structure are calculated and analyzed.And determine the optimal design parameters of the corresponding tunnel secondary lining structure.(3)Based on the geometric and structural models of the surrounding rock and secondary lining of the hydraulic tunnel,the mechanical model of the tunnel’s traditional lining structure and the model of the retractable lining structure are designed and manufactured.Model tests were carried out on the hoop stress and deformation of the lining under multi-level ground stress and internal water pressure.The test results show that under the same loading conditions of water pressure and vertical ground stress in the tunnel,the circumferential stress of the foursegment retractable lining structure is smaller than that of the traditional lining structure.The load borne by the surrounding rock under the lining of the retractable lining structure is greater than that under the traditional lining,indicating that the retractable lining structure can better adapt to the complex stress conditions of hydraulic tunnels,which is consistent with the theoretical analysis results and the numerical simulation analysis.