In-situ Experiment And Bearing Capacity Study Of Three-layer Lining For Water Conveyance Shield Tunnel Under High Inner Water Pressure

The water conveyance shield tunnel is an important part of the water resources allocation project.For meeting the needs of bearing high internal water pressure and excellent durability,the structural type has been developed from single-layer lining to double-layer lining or even multi-layer lining structure.The three-layer lining structure for water conveyance shield tunnel is a kind of combined bearing structural system composed of an outer segmental primary lining,a secondary self-compacted concrete lining and an inner steel tube.At present,under the real surrounding rock environment and high inner water pressure,the bearing capacity and calculation models of the structural system are rarely studied.Besides,insufficient experimental demonstration is existant.Based on the in-situ structural experiment of the Pearl River Delta Water Resources Allocation Project,this paper analyzes the bearing capacity of the three-layer lining structure for water conveyance shield tunnel under external surrounding rock pressure and inner test pressure.Subsequently,a three-dimensional numerical simulation model is established and verified its reliability by the experimental results.The mechanical responses of the structural system under the maximum working inner water pressure and the beneficial effects of the structural measures for setting waterproof cushion are further explored through numerical simulation.In general,the conclusions will provide an insight into the design and application for a similar water conveyance shield tunnel project.The main work and achievements of this paper are summarized as follows:(1)The engineering geology and hydrogeological conditions,overall structure design,monitoring arrangement and internal pressure loading scheme of the in-situ experiment are briefly described.(2)According to the monitoring results during the construction period,the distribution of water and soil pressure around the segment,the stress of rebars and the internal force state of the segment are analyzed and obtained;Through the monitoring results of internal pressure loading test,the deformation and stress state of the segment,self-compacted concrete and steel tube under the action of 0.75 MPa internal pressure are analyzed,from which the small deformation of the structural system as well as the large safety reserve are concluded.(3)After reproducing the in-situ experimental results,the three-dimensional finite element model of the three-layer lining structure is established to analyze the bearing capacity of the structural system under the maximum working internal water pressure of 1.05 MPa.However,the safety reserve of the structural system is still sufficient and the structural system can be optimized from two aspects: exerting the material property of the steel tube and reducing the possible operation risk.(4)Two factors,the waterproof cushion setting and different elastic modulus of the cusion,are simulated for the bearing capacity of the structural system.The deformation of the segment and steel tube,the stress of joint bolts and steel tube are obtained by numerical analysis.By contrast,setting low modulus waterproof cushion is more conducive to optimizing the original structural system.