Study On The Strata Disturbance And Mechanical Properties Of Lining Segment During GPST Tunneling Process

With the acceleration of urbanization in China,the application of shield tunnel has also became more extensive in our country.However,conventional shield tunnel construction requires the excavation of working shafts,which has significant effect on surrounding environment in congested urban area.Ground Pass Shield Tunneling(GPST)method is able to avoid the excavation of working shafts,it can reduce the effect on the surrounding strata during tunnel construction effectively.However,due to the technical characteristics of the method,the shield must be driven beneath different cover-depths during GPST tunneling process,thus,the construction environment is more complicated than conventional.The shield tunnel test section was employed as the GPST demonstration work between Nanjing South Railway Station and Lukou Airport Station in Nanjing,a detailed simulation is established by non-linear finite element method,which is used to systematic analysis the soil disturbance and mechanic behavior of lining segment during the tunneling construction process.The main research work and results are as follows:(1)Based on the in-situ test monitoring data of the shield tunnel of Nanjing South Railway Station and Lukou Airport Station(GPST).The soil disturbance mechanism and mechanic behavior of lining segment are analyzed under different cover-depths during GPST tunneling process in various aspects,including layered settlement and horizontal displacement of soil,soil pressure,pore water pressure,grouting pressure distribution and changes in the internal force of the lining segment.Which reveal the soil disturbance mechanism and lining segment deformation mode under different cover-depths of GPST during process.(2)Based on the Nanjing South Railway Station and Lukou Airport Station(GPST)shield test section,a detailed finite element model(FEM)is established,the finite element results are compared with the monitoring results and analyzed.The results show that the construction disturbance is mainly concentrated in the two phases,shield tunnel machine arrives and shield tail coming out.In which,layered settlement and pore water pressure will fluctuate before the shield tunnel machine arrives,due to the stress release of the soil in the process of the shield tail constantly coming out,the layered settlement will increase,but the pore water pressure will decrease.After the shield tail coming out completely and under the effect of grouting,the layered settlement and pore water pressure of soil will recover and stable gradually.Then,inward and outward displacement will happe in the boundary displacement mode of horizontaln,they are mainly affected by construction parameters.On the whole,there is deviation within a reasonable range between the finite element results and the monitoring results,but the rules are consistent,which testify the reliability of the finite element results.(3)Based on the 3D FEM numerical model,firstly,it analyzes the changes of ground settlement before and after the excavation of the retreating tunnel,and researches the impact of different factors on ground settlement,which include the internal friction angle,modulus elasticity in grouting layer,combination form of construction parameters and constructing shelter pile.The results show that increasing these parameters properly can restrain the value of ground settlement effectively,of which,the change of internal friction angle is more sensitive to the impact on ground settlement than modulus elasticity in grouting layer.Among the construction parameters,the supporting pressure can reduce the ground settlement more significantly than grouting pressure,and the construction of shelter pile plays a significant role in reducing the impact of ground settlement interaction.Secondly,analyzing the distribution of the internal force of the advancing tunnel lining segment caused by the retreating tunnel excavation,and relevant factors are studied,which include modulus elasticity in grouting layer,grouting pressure and the stiffness of tunnel lining segment.The results indicate that,in all these factors,the risk of tensile failure of lining segment in all working conditions is much higher than that of compressing failure,in which the variation of internal force and the stiffness of lining segment has a significant non-linear quadratic functional relationship.