Study On Mechanical Properties Of Double Lining Of Urban Deep Drainage Shield Tunnel

With the advancement of urbanization,urban waterlogging disaster is becoming more and more serious.As an important measurement to alleviate urban waterlogging,the deep-buried tunnel drainage system has been applied in some developed countries and shown a positive effect.In recent years,the related researches have received more and more attentions owing to the frequent occurrence of waterlogging in China.Due to the existence of internal water pressure,the mechanical behaviors of deep-buried drainage shield tunnels are quite different from that of traditional traffic tunnels.That is,a further study on mechanical properties of deep-buried tunnels is necessary.Based on the shield tunnel project of Wuhan Dadonghu Sewage Deep-buried Tunnel,this paper carried out the joint tests and numerical simulation analysis for the double lining drainage shield tunnel.The main research and results are as follows:（1）Combined with Wuhan Dadonghu Sewage Deep-buried Tunnel Shield Tunnel Project,this paper designed the test scheme of single lining joint,double lining joint（without water connection）and double lining joint（after water connection）for deep-buried drainage shield tunnel.The fabrication of specimen,selection of measuring instrument and modification of loading device are included as the main contents.（2）Through the joint test,the variation law of joint opening,bending stiffness and joint stress with bending moment and axial force were revealed,including all three stages as single lining,double lining（without water connection）and double lining（after water connection）.During the double lining（after water connection）stage,due to a lot of structural tension shared by the secondary lining,the segment can still keep compressive bending even the inner water pressure is large.The joint mechanical parameters of the shield tunnel of sewage deep-buried tunnel in Dadonghu District of Wuhan were determined.The maximum opening of the single lining joint is 2.15mm,the bending stiffness range is 10～50MN·m·rad^-1,the maximum opening of the double lining joint without water connection is 0.33mm,and the bending stiffness range is 20～200MN·m·rad^-1.After the double lining connected with water,the maximum opening of the joint is 0.72mm,and the bending stiffness ranges from 10 to110MN·m·rad^-1.（3）The three-dimensional shell-spring model is used to calculate and analyze the drainage shield tunnel,and the influence of different conditions parameters on the mechanical properties of the drainage shield tunnel is proved.With the joint bending stiffness increases from 10 MN·m·rad^-1 to 100 MN·m·rad^-1,the segment axial bending moment increases,the secondary lining axial bending moment decreases,the structural deformation decreases,the distribution of structural internal forces become more uniform.Moreover,the internal force of the structure is more sensitive to the change of bending stiffness value while there is internal water pressure.In addition,the internal water pressure has hardly effect on the bending moment of the structure,while the axial force of the structure is sensitive to it.With the increase of the internal water pressure from 0MPa to 0.4MPa,the axial force pressure of the segments decreases and even behave as a tension eventually.On the contrary,the tension of the axial force of the secondary lining increases rapidly.While a large internal water pressure,the axial force tension of the segments would be delayed by the relevant large external soil and water load,which is beneficial to the tunnel structure.（4）The overlapping structure enhances the force transfer between the segment and the secondary lining,and its combined bearing effect of the segment and the secondary lining is better than that of the composite structure.When the internal water pressure is large,the tangential spring stiffness of the joint surface increases,the axial force pressure of the segment and the axial force tension of the secondary lining decreases.A significant optimization of the structural bearing capacity during water operation can be achieved by improving the adhesive force between the segment and secondary lining.While there is no internal water pressure,the initial release ratio of surrounding rock load and the axial force pressure of the segment decreases,the external water and soil load that can be shared by the secondary lining and the axial force pressure of the secondary lining increases.As a result,the axial force tension of the secondary lining would decrease while there is an internal water pressure.Therefore,the secondary lining should be carried out as early as possible,leading the secondary lining and segments share the external soil and water load soon,reducing the axial force pressure of the segments at the initial stage and the axial force tension of the secondary lining after the tunnel operation,which is conducive to the stress of the tunnel structure.