Researh On The Influence Of The Adjacent Underground Gas-Pipelines By Shield Tunneling Construction

As the hysteresis of the urban subway construction, the subway line will inevitably pass through underground municipal pipelines, thus the safety of pipelines and its normal use will be affected. In the process of the tunnel construction, the internal force and deformation of the adjacent underground pipelines present nonlinear variations, to study the disturbance law is more helpful to ensure the safety of adjacent underground pipelines and direct the construction of the tunnel project. Through a case study on the gas-pipelines and its concrete casing engineering vertically crossed beneath by shield tunnel in Beijing, surrounding rock-tunnel-pipeline3-D coupling calculation model was established by utilizing the finite element software, the process of right and left tunnel passing beneath was imitated by using element "birth and death" principle and Newton-Raphson Algorithm on the basis of the surrounding rock-load model.1) Combined with underground pipe materials, structure mechanical characteristics, the neighboring relation between the underground pipeline and tunnel, the soil settlement law by tunnel construction, the failure modes of concrete casing are longitudinal sections’bending-breakage or shear-breakage and joints’corner-destruction or cracking-destruction; the failure modes of the high pressure gas-pipeline are tension-destroying, compression-destroying and shear failure.2) The concrete casing’s maximum positive and negative moment, as well as maximum positive and negative axial force change with the crossing, the growth of axial force is greater than moment’s, the occurrence of stretch-bending breakage is easier; the Maximum opening value of joints is0.18mm, the largest joint Angle is0.0103°, which far miss the ability of joints against disengage. As for DN700high pressure gas-pipeline,the growth range of the first and third principal stress are little, as well as Mises stress, and the safety coefficients are all above5, X-direction stress and YZ-direction shear stress as one of the stress components changes more obviously,the growth rate are14.8%and6.6%respectively. As for DN500sub-high pressure gas-pipeline,the growth range of the first principal stress and Mises stress are little, the safety coefficients are all above18, Although the third principal stress (compressive stress) grows more than25%,its safety coefficients is high relatively, the growth rate of X-direction stress and YZ-direction shear stress are14.8%and6.6%respectively. 3) From the disturbance response of concrete pipes and high pressure gas pipeline, the worst states of the underground pipeline may happen in the following four kinds of state:the moment of the right or left single tunnel is reaching below a certain location of the pipeline, at the end of the right or left single tunnel construction; For the pipeline with good integrity in the utility tunnel, the final value can used to judge the greatest stress in the history state after inner force comparation.4) The surface slope and the surface settlement curve can be used for preliminary judgement of pipeline’s safty. The concrete casing settlement curve is Gauss curve in the crossing of the tunnel construction, compared with the actual monitoring data; they are fully similar at settlement maximum, different subsidence value.