Experimental Study On Deformation Mechanism Of Existing Underground Pipelines Caused By Shallow Buried Tunnel Adjacent Construction

The urban underground projects such as subway tunnel and utility tunnel promotes the development and utilization of urban underground space and alleviates the problem of land shortage at the same time.However,due to the fact that the route selection of related project construction usually extend along the urban main road where the surrounding engineering environment is complex,passing through a great amount of existing underground pipelines becomes inevitably.The unloading effect of tunnel excavation induced ground movement and leads to the deformation of adjacent underground pipelines,which is a potential threat to the normal use and safety of pipelines.In order to ensure urban tunnel construction proceeds safely and orderly without affecting normal operation of existing pipelines,it is necessary to study the influence of tunnel undercrossing on existing continuous pipelines,the prediction of the deformation response of pipelines after construction and the judgment of the safety status of pipelines.In this paper,the existing pipeline under a single tunnel is taken as the research object,both similar model tests and theoretical analysis are adopted.The tunneling induced greenfield soil displacement and the response of pipeline to tunnel excavation are studied.The main research contents are as follows:(1)Based on the scale model test,transparent soil testing technique is introduced.Meanwhile,by improving the test method and post-treatment were,the three-dimensional deformation of ground are obtained.The tunneling induced ground movement under different conditions in model tests are studied.According to the vertical variation of the soil settlement,the depth and shallow buried properties of the tunnel whether are discussed.(2)Based on Winkler foundation beam theory,an analytical model for the tunneling induced bending response of continuous pipelines is established.The free-field ground deformation can be described by modified empirical formula or analytical solution.The calculation method of bending deformation of pipelines under oblique crossing condition is also obtained.Security evaluation process of pipeline after bending deformation is put forward.The measured ground settlement data from the transparent soil model test were applied to the analysis model,and the distribution of pipeline bending deformation under various working conditions was obtained.(3)The analytical solutions for estimating the axial response in a buried pipeline due to ground movements caused by tunnel construction is also established.The solutions combine empirical formula or analytical solutions for tunnel-induced,free-field horizontal ground movement in a plane orthogonal to the heading with Winkler models for pipe-soil interactions.At the same time,the oblique intersection between pipeline and tunnel is also considered.Finally,the horizontal displacement data of ground measured in the transparent soil model test were applied to the analytical solutions,therefore the axial deformation distribution of pipelines under various working conditions was obtained.(4)Using the finite element software ABAQUS,the original scale model of the transparent soil model test was numerically analyzed.By comparing the bending and axial results of pipeline of finite element analysis and that of Winkler foundation beam theory model,the reliability of the theoretical model was verified.