Research On The Law Of Ground Settlement And Pipeline Deformation Under The Coupling Effect Of Shield Construction And Adjacent Pipeline Leakage

Shield tunneling method has become the main method of urban subway tunnel construction in China due to its advantages of high automation,small influence on surface traffic and free from climatic conditions.Shield construction inevitably disturbs the surrounding soil,which makes the adjacent underground pipelines bear additional load and then deform.Excessive deformation will cause pipeline leakage,even fracture,pipe burst and other accidents.Especially in unsaturated strata,the diffusion of leakage water changes the physical and mechanical properties of soil,intensifies the pipeline deformation and ground settlement caused by shield construction,and has higher risks and greater hidden dangers.Therefore,under the influence of leakage water,the risk assessment and control of double-line tunnel shield construction near municipal pipelines have important practical engineering significance.This paper takes the study of ground settlement and pipeline deformation as the main line,adopts the research methods of laboratory test,theoretical analysis,model test and numerical simulation,and focuses on the pipe-soil interaction mechanism under shield construction disturbance,the theoretical solution of ground and pipeline deformation caused by viscoelastic space shield construction,the influence zone of shield construction near the existing pipeline and the stress and deformation law of ground and pipeline under the influence of pipeline leakage.The basic physical and mechanical parameters of typical unsaturated clay in Hefei area were tested.The variation law of soil suction and soil-water characteristic curve were studied by filter paper method and temperature-humidity method.Based on the test results,the applicability of the four commonly used matrix suction prediction models and the soil suction test results in this study was analyzed.The results show that the modified FX model has high fitting accuracy,which is in line with the change law of matrix suction of Hefei unsaturated soil.In addition,the influence of matric suction on the shear strength of soil was further studied.The measured cohesion and the contribution of matric suction increased first and then decreased with the increase of matric suction.When the matric suction was 242.45 kPa,the influence reached the peak of 91.13%,and then gradually decreased,and tended to zero when the volumetric water content decreased to 22.82%.Based on the principle of two-stage method,combined with the generalized Kelvin model and Mindlin basic solution,and considering the influence of shield tunneling pressure,shield shell friction,grouting pressure and ground loss,the three-dimensional viscoelastic solution of ground displacement and the time-domain solution of pipeline deformation caused by double-line tunnel shield construction are derived.The calculation results show that the theoretical solution can clearly explain the phenomenon of the surface uplift in front of the shield excavation and the settlement of the rear surface under the action of multiple factors,and it can predict the most unfavorable section of the pipeline caused by the shield construction,and the calculation results of ground displacement and pipeline deformation are basically consistent with the field measurement.In addition,the spatio-temporal evolution law of the influence of viscoelastic parameters,geometric parameters and shield parameters on soil displacement is further discussed.Based on the self-developed model test system of double-track tunnel shield tunneling through existing pipelines,the ground settlement and pipeline deformation caused by shield construction without pipeline leakage and small-scale leakage are studied.The non-leakage model test results show that the change of soil settlement within the measuring point range can be divided into three stages:slow increase,rapid increase and stable stage.After the single-line tunnel is connected,the difference between the theoretical and experimental results of ground settlement is 0.6 mm.When the double-track tunnel passes through,the deviation increases to 3.9 mm due to the repeated disturbance of secondary excavation.The results of small-scale leakage model test show that the final diffusion of leakage water is mainly vertical;Under the influence of water leakage,after the single-line tunnel is connected,the ground settlement increases by 45.5%on average,and when the double-line tunnel is connected,the ground settlement increases by 24.5%on average,and the settlement increment increases with the increase of depth.Affected by the repeated disturbance of ground,the strain of the pipeline above the central line of the two tunnels increases by 79%in the secondary excavation of the tunnel,and the strain increment at the bottom of the pipeline is larger than that at the top.Combined with the change trend of soil pressure around the pipe,it can be seen that the decrease of soil pressure at the bottom of the pipeline is stable after reaching the load value imposed by the cylinder,indicating that the shield excavation makes the pipe-soil separation at the bottom of the pipeline in a small range of leakage.Considering the impact of pipeline leakage,a unidirectional coupling calculation model for shield construction and pipeline leakage is established,and the rationality of the model is verified by combining theoretical calculations and test results.Comprehensive consideration of the two factors of pipe-tunnel vertical clear distance H and tunnel horizontal clear distance S,16 kinds of analysis conditions are established.Numerical calculation results show that the strength and weakness of shield construction divided by pipeline settlement is higher than that of ground settlement,so the former has a higher safety factor.In addition,taking into account the influence of different vertical leakage ranges of pipelines and different horizontal leakage lengths,9 numerical calculation conditions are established to analyze the force and deformation laws of formations and pipelines and the distribution characteristics of plastic zones under the coupling effect of shield construction and pipeline leakage.Figure[92]table[28]reference[173]...