In-situ Test And Numerical Study On Bearing Capacity Of Water Conveyance Shield Tunnel Lining Structures

The water conveyance tunnel of the Pearl River Delta Water Resources Allocation Project has a buried depth of 40-60 m,and its internal water head is as high as 155 m.Being buried deeply and high internal pressure conditions bring difficulties to the design of lining structures.In order to select a proper structure type for tunnel lining under long distance complex geological conditions,this paper carried out the in-situ tests of water conveyance tunnel linings.Besides,the bearing capacities and applicable conditions of different linnings were studied.Based on the in-situ tests,this paper analyzed the bearing performances of four typical linings under internal pressure.Combined with numerical simulation methods,the bearing capacities and mechanical applicabilities of four typical lining structures were furtherly studied under several geological conditions.The results could provide references for the structural selection of water conveyance tunnel linings with inner pressure.The main work and conclusions are summarized as follows:(1)The monitoring method combined distributed optical fibers and traditional sensors was used.Moreover,an internal pressure simulation system of called ‘high-pressure bladder-reaction frame – pump’ was designed to carry out the loading and unloading tests.It turned out that the survival rate of the monitoring sensors reached 97.5%.In addition,the tasks of internal pressure control were stably completed by the proposed system.Afterwards,based on characteristics of the linings,the failure criterion of the lining structures was proposed.(2)According to the in-situ results,the deformation characteristics and bearing performance of the four typical lining structures under internal pressure were analyzed.The analysis conclusions are summarized as follows: the single segment linings reaches the limit of joint opening at an internal pressure of 0.36 MPa.The ultimate internal pressure that double-layer linings can bear is controlled by concrete cracking on the surface of the inner linings.In separately bearing conditions and jointly bearing conditions,the responses of the‘segment-SCC-steel tube’ linings are relatively slight at an internal pressure of 0～0.75 MPa,and they have not yet reached the bearing limit.(3)For analyzing the internal pressure bearing capacities of four types of linings,four three-dimensional numerical models were established,and their effectiveness was verified by the in-situ test results.The analysis results can provide a foundation for further research on the applicabilities of different lining structures under different geological conditions.(4)Finally,numerical analyses of the internal pressure bearing performance and applicabilities for the four typical linings in the the stratum with 10～500MPa/m resistance were carried out.The key controlling indexes of the bearing capacities and applicabilities for different geological conditions of the linings were obtained.The upper internal pressure bearing limits of single segment linings and segments-reinforced concrete linings are0.25～0.45 MPa and 0.55～0.85 MPa,respectively.Those for separated and superimposed‘segment-SCC-steel tube’ linings are 1.5～3.0MPa and 1.4～2.7MPa,respectively.