Prediction Technology Of Adjacent Underground Pipelines Damage Caused By Excavations Dewatering

Dewatering will greatly reduce the underground water levels of foundation pitand its surrounding areas, which can cause adverse reactions such as the deformationof pipelines near the pit. The underground pipeline is a project of the city’s lifeline,and plays an essential role in the city life. Once a failure comes up, tens of thousands,even millions of people’s normal life will be affected. Among the reasons for theunderground pipelines accidents, one is the uneven settlement of pipeline foundation.Therefore, engineers should pay more attention on predicting the deformation ofsurrounding underground pipelines which caused by the reduction of the undergroundwater levels before the construction of foundation pit project.Take the actual dewatering engineering for example, with the help of theoreticalanalysis, field measurement and numerical calculation, the researches on theproblems of the deformation of underground pipelines caused by dewatering are asfollows. Summing up the ways of well-point dewatering and its conditions andintroducing the basic methods of seepage computation briefly as well as stating whydewatering causes surface settlement. Introducing the types, laying technology,construction methods and failure mode of underground pipelines, and alsosummarizing the interaction between underground pipelines and the surrounding soil.On this basis, put forward the concept of underground pipelines gradientsedimentation, and get the formual that can calculate the deformation of pipelinejoints. Settlement gradient and joint curvature are chosen as the deformation statetargets for flexible pipelines; and principal stress in pipelines is chosen for rigid jointpipelines. Finally, based on practical excavation project, the three-dimensional finiteelement analysis model is established in ABAUQS, considering the interactionbetween soil and pipeline. The distribution of groundwater level after dewatering anduneven settlement of underground pipeline due to water level decreased is simulated.Then the results of numerical simulation are compared with the measured results, andthe feasibility of numerical simulation model and parameters is confirmed. Dewatering depth had been chosen as one significant factor among all affectingaspects on adjacent underground pipelines deformation, which may be the input for3-D FEA model. The deformation state targets of adjacent underground pipelineswere then analyzed. And then proposes the strategies for reinforcing and protectingthe adjacent underground pipelines basing on the above analyzing results：thestrengthening regional of flexible pipeline appears near the boundary line ofdewatering area; the strengthening regional of rigid pipeline appears near the axis ofdewatering funnel. Summing up the controlling criterion for underground pipelines’deformation and proposing the standard of pipeline damage. Then constructingfunction relationship of pipeline damage and its deformation basing on Powell’soptimized algorithm so that predicting the damage of underground pipelines whenmaking plans for dewatering.