Simulation Research On Ground Deformation Caused By CBM Pipe Jacking Construction

In recent years,since CBM is not only a high-quality clean fuel,but also an important chemical raw material,the CBM industry has developed rapidly.Affected by topography,mineral resources,etc.,the laying of coalbed methane pipelines faces severe challenges,and directly affected by the humid environment,problems such as pipeline perforation and corrosion are likely to occur.Pipe jacking is widely used because it can take into account the jacking effect in stable soil layers and unstable soil layers.However,compared with operation techniques such as pipe buried,there are still many areas for improvement in construction technology and operation.Therefore,in-depth analysis of the technical defects existing in the pipe jacking construction operation in unstable soil layers is carried out,and targeted improvement suggestions are put forward for the existing defects.Taking the main pipe construction of gas layer in a certain area using pipe jacking construction as the background,the numerical simulation of the construction process of coal seam gas pipe pipe jacking was carried out by finite element ABAQUS.Firstly,according to the soil layer conditions and field working conditions,the soil layered model is simplified.From the surface to the bottom,there are plain fill,quicksand layer,clay layer and weathered granite layer,the thicknesses are: 3 m,8 m,12 m respectively.m,15m;the buried depth of the pipeline is 12 m,the outer diameter of the pipe jacking is 500 mm,the jacking is to 30 ～ 50 m,and the length of each section of the steel pipe for the pipe jacking project is 5 m.The horizontal length of the model is 50 m,and the vertical direction is 50 m,that is,the size of the soil model is 50 m×22 m×50 m.By changing the method of activating and passivating the corresponding grid,the actual deformation value of the surrounding surface caused by the horizontal pipe jacking construction is simulated,and it is compared with the deformation data monitored on site.Using qualitative analysis,numerical simulation verification,on-site monitoring and other means,the following research results are obtained:(1)Under the action of thrust,the maximum horizontal displacement of the soil is located at the depth of the pipe jacking axis,while the soil located directly in front of the propulsion surface There will be an uplift with a maximum vertical height of 2 mm in the body area.On the other hand,the surface subsidence will occur due to the action of the jacking force,and the maximum subsidence distance will reach 2.3 mm;(2)Based on the longitudinal analysis angle,the 2D range in front of the jacking face is obtained.There is a significant disturbance phenomenon in the soil,and a significant increase in the displacement change can be observed in the horizontal direction of the land;(3)Based on the lateral analysis angle,it is found that there is a significant disturbance phenomenon in the soil in the 1D range around the pipeline;(4)Based on the From the perspective of vertical analysis,it is found that the vertical deformation does not have a significant effect on the soil in the 2D range above the pipeline,and the increase rate of the horizontal displacement of the soil gradually decreases,and the final displacement value tends to be stable.