Experimental Study On The Mechanical Response Of Oil And Gas Pipelines Under Ground Subsidence

In recent years,our country’s long-distance oil and gas pipeline industry has developed rapidly.The serviceability loss of oil and gas pipelines caused by the ground subsidence has occurred in many cities.Therefore,research on the mechanical response characteristics of long-distance oil and gas pipelines subjected to the ground subsidence has been significant.This paper comprehensively uses the methods of experiment and theoretical analysis to study the mechanical response of oil and gas pipelines underground subsidence.The main research contents and results of this paper are as follows:(1)The ground subsidence test was carried out based on the pipeline safety test platform under the action of ground subsidence.The soil deformation,pipe strain and earth pressure around the pipe were measured during the subsidence process,and the characteristics of soil deformation,the distribution of pipeline strain and the distribution of earth pressure around the pipeline were obtained.The strain zone of the pipeline were obtained.The test results show that In the settlement range,the soil pressure on the upper part of the pipeline increases,and the earth pressure on the lower part decreases;in the non-settlement range,the earth pressure on the upper part of the pipeline decreases,and the earth pressure below the pipeline decreases.The axial strain and hoop strain of the pipeline increase with the expansion of the settlement area and the increase of the settlement amount.The maximum axial strain and the maximum hoop strain of the pipeline appear at the centerline of the pipeline,which are the axial tensile strain and the hoop strain respectively.The whole process is mainly based on aixal strain.(2)A rapid ground subsidence test was carried out.The soil deformation,pipe strain and earth pressure around the pipe were measured during the subsidence process,and the characteristics of soil deformation,the distribution of pipeline strain and the distribution of earth pressure around the pipeline were obtained.The test results show that rapid settlement is mainly divided into two stages.In the first stage,there is still a large amount of soil on the upper part of the pipeline,and a cone-shaped collapse area is formed in the settlement range;the maximum strain of the pipeline appears at the centerline of the pipeline in the settlement range,which is the axis.Compressive strain.In the second stage,the soil in the settlement range all collapsed,and the pipeline is completely exposed;the maximum strain appears in the non-settlement range,which is the axial tensile strain.(3)By changing the moisture content of the backfilled sand,we carried out the ground subsidence test under different moisture content,measured the pipeline strain and the soil pressure around the pipe during the soil settlement,and studied the influence of the change of the moisture content under the ground subsidence on the pipeline strain and the soil around the pipe.The test results show that in the process of ground subsidence,the increase of water content will reduce the earth pressure around the pipe and reduce the axial strain and hoop strain of the pipeline,but the influence of water content on hoop strain is smaller than the axial strain.And the greater the settlement,the more significant the effect of the change in water content on strain.(4)Set up two sets of stacking settlement tests with different stacking lengths to measure the pipeline strain,soil deformation and soil pressure around the pipe during the soil settlement process,The influence of the existence of the upper piled load and the change of the piled load length on the pipeline strain,soil deformation and the distribution of earth pressure around the pipe in the process of ground subsidence is studied.The test results show that the existence of the heap load will increase the deformation of the soil and the axial strain of the pipeline.Under the circumstance that the stacking weight remains the same,the increase of the stacking length will reduce the soil pressure at the upper and lower part of the pipeline,but increase the soil pressure on the side of the pipeline,and at the same time will reduce the extreme value of the pipeline in the axial direction,and the axial strain.The distribution is more "even".(5)Fitting the vertical displacement of the soil under the ground subsidence based on the similar Gaussian curve,it is found that the vertical displacement of the soil conforms to the modified Gaussian curve,and the increase of the water content will increase the vertical displacement of the soil.The displacement gradually decreases from the soil at the location of the pipeline to the surface soil.Based on the modified Marston earth pressure calculation formula,combined with the soil deformation during the settlement process and the earth pressure distribution around the pipe obtained in the test,The calculation method of earth pressure considering the cohesive force between soil columns and the redistribution of stress in the transverse and longitudinal sections of the foundation settlement is deduced The calculation result is compared with the test result and it is found that the two are relatively close.The mechanical analysis of the pipelines in the non-settlement range and the settlement range were carried out.According to the deformation coordination conditions at the interface,the response analysis of the entire pipeline was obtained.