A shared borehole approach for coal-bed methane drainage and ground stabilization with grouting

•A shared borehole approach proposed for CBM drainage and grouting.•A temporal model combining gas drainage and grout injection is proposed.•The proposed approach was tested in a Chinese coal mine longwall panel.•Interaction of CBM drainage and injection was tested using a case study.

In underground longwall coal mines, the risks of surface subsidence and coal-bed methane (CBM) emission are generally controlled separately (e.g., subsidence mitigation by overburden stabilization using grout injection, and pressure-relief CBM drainage using surface boreholes); however, some longwall panels require both gas drainage and ground stabilization. For this purpose, we propose a shared borehole approach for ground stabilization grouting and adjacent seam pressure-relief CBM drainage by using mining-induced fractures and voids. In this method, overlying seam pressure-relief CBM is drained through a surface borehole during extraction of a longwall panel, whereas grout injection is applied to stabilize the ground using the same borehole following drainage. A combined drainage–injection model that determines the allowable lag distance for grout injection is proposed. The effectiveness of the shared borehole approach was tested at a longwall panel in a Chinese coal mine. No obvious interactions between the injection and drainage processes were detected during the case study, verifying the effectiveness of the shared borehole approach.