Research On The Interaction Mechanism Of Shield Tunneling Under Existing Tunnel

The interaction mechanism between a two-lane shield tunnel and an existing tunnel underpassing obliquely has been a widespread concern in the engineering community and is still limited to a cursory knowledge.Especially in the construction of subway tunnels in undulating mountainous cities,internal forces and deformations will inevitably occur in existing tunnels.Relying on the topic of "Research on Key Technologies of Underpassing Existing Railway Construction in Guiyang Urban Rail Transit Interdistrict Tunnels",the research is carried out in terms of theoretical analysis and research,refined numerical simulation,analysis of field measurement data and factors influencing the underpass construction for the shield structure underpassing existing tunnels in Guiyang Metro Line No.3 Taoyuan～Hua.The main research works are as follows:(1)Considering the slurry injection fluid as Bingham fluid,the analytical formula of non-uniform injection pressure theory is derived;assuming the shield shell as hollow shell steel pipe pile,the formula of frictional resistance between shield shell and surrounding rock is derived with reference to the calculation model of pile-rock interface;based on Winkler elastic foundation beam model,the existing railroad tunnel is considered as Euler-Bernoulli beam,and the displacement control equation is established to derive the existing Theoretical solution of vertical displacement at tunnel axis.(2)To establish an oblique numerical model of the double-lane shield tunnel underpassing the existing tunnel to reveal the deformation of the ground,the deformation of the existing tunnel and the mechanism of interaction between the old and new tunnel caused by the oblique crossing underpassing construction.The results show that: the existence of existing railroad tunnel has a certain "blocking" effect on the upper ground deformation;the oblique underpass leads to the "asymmetric" distribution of the settlement curve of the existing tunnel structure and local torsional deformation.(3)From the analysis of the measured data,it can be seen that the impact range of the shield penetrating the existing tunnel is within the front and rear 32 m,and the measured data in the field is similar to the overall pattern of the numerical simulation results.The settlement of the vault and the surface during the shield tunneling process can be divided into three stages: Stage Ⅰ(prior settlement stage),Stage Ⅱ(settlement before excavation and settlement through underpassing stage),and Stage Ⅲ(hardening stage of slurry off the end of the shield).(4)Based on the finite element analysis method,the factors affecting the deformation of existing tunnel caused by shield underpass were studied and sensitivity analysis was conducted to conclude that the ground conditions are the main influencing factors causing the deformation of existing tunnel.