Optimal Design of a Protective Coal Pillar with a Buried Pipeline in a Thick Loose Layer in Western China: Methodology and Case Study

At present, the horizontal distance between the surface subsidence boundary and the panel is typically selected as the width of the protection coal pillar with the buried pipeline at the gas–coal integrated mining area (traditional method), which causes abundant coal resources to be unrecoverable. To improve the recovery rate of coal resources, the protective coal pillar of the pipeline is optimally designed. First, the Gaussian function equation of the surface subsidence curve is investigated using the probability integral method (PIM). The elastic deformation limit of the pipeline within the subsidence basin was analysed. Then, the failure probability of the pipeline was calculated by analysing the multifactor indicators that affect it. The elastic deformation limit was modified by considering the time effect of the surface subsidence and the failure probability. Next, by analysing the pipeline deformation in the mining subsidence basins, a novel method for the optimal width of the protective coal pillars with buried pipelines in the thick loose layer undermining is proposed. Meanwhile, the verification method and protection measures for pipeline safety are proposed. Finally, theoretical analysis and engineering examples are used for analysis and verification. The results show that the surface subsidence curve caused by critical mining can be expressed by the Gaussian function when the buried depth/thickness ratio (DTR) of the flat coal seam is greater than 40–60 under thick loose layer. Using Panel 132201 as an example, the prediction method reduced the width of the protected coal pillar by 14 m and increased the panel recovery rate by 3.11% while ensuring the safety of the pipeline. This method effectively promotes coordinated mining between oil–gas and coal resources and provides a reference for the design of pipeline protection coal pillars in gas–coal integrated mining areas.