Study On Environmental Effects Of Large Diameter Double Line Parallel Pipe Jacking

Pipe jacking is commonly used in the construction of various underground pipelines and channels,and has become one of the main construction methods for urban underground space development.At present,the construction environment faced by the pipe jacking is becoming increasingly complex,which inevitably has adverse effects on the surrounding environment.Based on a power pipe jacking project in Hangzhou,this paper analyzes the surface settlement and the impact of the underlying existing subway tunnel caused by pipe jacking construction through field measurement,theoretical analysis and two-dimensional finite element simulation.The main research content and work of this paper include:1.Based on the measured data of pipe jacking construction site,the environmental impact of large-diameter double line pipe jacking passing through the existing operating subway tunnel from above was analyzed in detail,including the distribution of surface transverse settlement,the development of surface settlement with time,and the variation law of subway tunnel heave,and the applicability of Peck formula in the prediction of surface settlement induced by pipe jacking was discussed.2.A two-stage simplified analysis method for the response of the underlying existing shield tunnel caused by pipe jacking construction considering the buoyancy effect was proposed.The floating phenomenon and triggering conditions during the jacking process of large diameter pipe jacking was analyzed.Based on previous research,a soil convergence model considering the uplift effect during pipe jacking construction was proposed and the stratum displacement solution was also obtained.The existing subway shield tunnel below was simplified as an Euler-Bernoulli beam resting on Pasternak elastic foundation beam,and the vertical displacement and bending moment responses of the existing shield tunnel below were calculated by finite difference method.The comparison with the measured results verified the rationality of the proposed method,and parameter impact analysis was further conducted.3.A prediction method for surface settlement caused by pipe jacking excavation under adjacent river conditions was proposed.A simplified analysis model was established based on the construction conditions of the pipe jacking near the existing river channel,and an analytical calculation model was established based on the virtual mirror technology.The final surface settlement was obtained through the correction of non-uniform convergence of the soil,which will provide a new approach for predicting soil displacement caused by tunnel excavation under complex boundary conditions.4.By Using Plaxis2 D finite element software,the distribution and development law of surface settlement caused by double-line pipe jacking construction was studied.The shrinkage ratio parameters of pipe jacking tunnel can comprehensively reflect the ground loss caused by various effects during pipe jacking construction.Adopting different tunnel shrinkage rates can simplify and quickly analyze the environmental impact of double line parallel pipe jacking construction.It is found that the time dependent settlement of the surface caused by pipe jacking excavation is significantly smaller than the measured results if the dissipation of excess pore pressure through consolidation analysis or a soil creep model is considered.Further analysis was conducted on the impact of thixotropic slurry grouting pressure and disturbance of soil caused by prior pipe jacking construction.The study shows that the disturbance of soil around the pipe caused by pipe jacking excavation will exacerbate the environmental impact of subsequent pipe jacking.Therefore,the thixotropic slurry pressure should be appropriately increased during subsequent pipe jacking construction.