Study On The Characteristic Of Upper Pipeline Deformation In Goaf Of Adjacent Steep Coal Seam

With the continuous development of economy and society,China’s demand for oil and gas is also increasing,and the construction of gas transmission pipeline is very important.In the process of laying gas transmission pipeline,it is inevitable to encounter more complex geological conditions,such as crossing coal seam goaf,high and steep slope,ground collapse,crossing lakes and rivers,etc.these factors will affect the safe operation and service life of gas transmission pipeline.Especially when the pipeline passes through the goaf,the surface deformation of the goaf may cause the bending deformation of the pipeline.Once the pipeline is bent or suspended,it will be very dangerous,and in serious cases,it will cause the leakage of transported substances in the pipeline.Therefore,it is necessary to study the deformation law of pipeline under the influence of goaf for the safe operation of pipeline.Taking the gas transmission pipe of Qianjiang Shaoguan section passing through Chashan and chashannan coal mine goaf as the research background,this thesis understands the stratum lithology,coal mining,geological structure and inclination of each coal seam in the steep coal seam goaf,analyzes the surface deformation mechanism of the coal seam goaf,as well as the interaction and stress analysis of the upper pipe soil under the influence of the goaf,Through numerical simulation and similarity simulation,the influence of the goaf of steep coal seam on the upper pipeline is studied.The deformation model of pipeline under the influence of adjacent steep coal seam goaf is established through numerical simulation,and the influence of steep coal seam goaf on pipeline under the condition of different coal seam inclination is analyzed.The numerical simulation results show that with the increase of coal seam inclination,the vertical displacement of the pipeline is basically consistent with the lower soil subsidence;The additional axial stress of the pipeline decreases gradually with the increase of the dip angle of the coal seam;Through the theoretical calculation of the sum of the axial stress generated by the internal pressure of the pipeline and the additional stress vector of the pipeline,it is concluded that the axial stress of the pipeline is less than the critical failure stress of the pipeline under the conditions of three coal seam dip angles,indicating that the pipeline is in a safe state.The similar simulation results show that the development degree of fractures decreases with the increase of the distance from the goaf;The pipeline produces two maximum tensile stresses at 55 cm and 114 cm of the model surface.It can be judged that the edge range of pipeline subsidence is 55 cm ～ 114 cm.Therefore,according to the geometric similarity ratio,it can be known that in the actual study area,the subsidence and bending range of the pipeline corresponds to 180 m ～ 380 m of the surface of the study area,and the pipeline in this area should be monitored.According to the numerical simulation and similar simulation results,the pipeline in the study area is in a safe state under the influence of 11 coal and 12 coal goaf.The research results have certain theoretical guidance and reference value for studying the safety of the upper pipeline in the goaf.