To reveal the influence of water accumulation in open pits on the stability of boundary coal-rock pillars, this study investigates a boundary coal-rock pillar between an underground coal mine and an adjacent open pit in western China. Coal-rock physical property tests, hydrochemical analysis, permeability tests, and theoretical calculations of water-resisting coal-rock pillars were conducted to examine seepage channel development, physical property changes, and stability evolution under long-term water accumulation. The results show that the mechanical strength of coal and rock specimens decreases under the saturated state. The average uniaxial compressive strength reduction of rock specimens exceeds 40%, while that of coal specimens is 7.6~18.2%. The tensile and shear strengths decrease by 30.0~57.1% and 7.5~34.6%, respectively. The hydraulic conductivity of intact specimens is mostly 10-4~10-3m/d, whereas that of fractured specimens increases to 10-3~10-2m/d. The calculated width of water-resisting coal pillars increases by 19.7~21.9% under long-term water accumulation. Long-term water accumulation in the open pit changes the external hydraulic boundary of the boundary coal-rock pillar, allowing water to migrate inward along bedding planes, joints, primary fractures, mining-induced fractures, and coal seam pores. This process promotes pore-fracture connection and seepage channel formation, weakens particle cementation and structural-plane shear resistance, and reduces the structural integrity, bearing capacity, and water-resisting capacity of the coal-rock pillar. Therefore, the stability deterioration of boundary coal-rock pillars is a continuous process involving channel formation, sustained seepage, strength degradation, fracture development, permeability enhancement, and further stability reduction.

Open-pit coal mine slope spalling events are rarely fully documented with sufficient samples, and the precision of publicly available monitoring data is inconsistent. To address these problems, this study develops a causality-oriented anomaly identification method that fuses four indicators: velocity, acceleration, persistent deviation, and phase change. Using the 25 May 2021 spalling event at the South Open-Pit Coal Mine (Xinjiang) as the main case, the analysis was based on 20 displacement measurements tabulated in the literature. Hourly replay was conducted using backward differencing and dual historical windows that contain only data already arrived at each time step, with baseline statistics frozen. Under the main setting, the fusion threshold was 1.351, and the first threshold exceedance occurred at 00:00 on the event day—9 h ahead of the field record; however, this time point involved a reversal of displacement direction and therefore cannot be directly interpreted as pre-failure acceleration. Among the 25 parameter sets tested, 6 triggered 15 h early, 17 triggered 9 h early, and 2 triggered 3 h after the event. For three externally digitized curves, the numbers of fused threshold exceedances were 1, 0, and 2, respectively; pixel-level perturbations could alter the triggering outcome, and exploratory phase-trajectory gating did not reduce exceedances on the periodic curve. The results support using the fused score for ranking historical anomalies and for local state re-examination, but are not yet sufficient to demonstrate warning reliability or a generalizable lead time on independent events. Engineering warning reliability still requires validation with independent raw monitoring data and complete event background records.

To reveal the influence of water accumulation in open pits on the stability of boundary coal–rock pillars, this study investigates a boundary coal–rock pillar between an underground coal mine and an adjacent open pit in western China. Coal–rock physical property tests, hydrochemical analysis, permeability tests, and theoretical calculations of water-resisting coal–rock pillars were conducted to examine seepage channel formation, physical property changes, and stability evolution under long-term water accumulation. The results show that the mechanical strength of coal and rock specimens decreases under the saturated state. The uniaxial compressive strength of rock specimens decreases by 8.75–50.64%, while that of No.2⁻² and No.3⁻¹ coal specimens decreases by 17.72% and 25.01%, respectively. The tensile strength decreases by 24.59–59.11%, and the shear strength decreases by 4.36–45.96%. The hydraulic conductivity of intact specimens is mostly 10⁻⁴~10⁻³ m/d, whereas that of fractured specimens increases to 10⁻³~10⁻² m/d. The calculated width of water-resisting coal pillars increases by 19.7~21.9% under long-term water accumulation. Long-term water accumulation in the open pit changes the external hydraulic boundary of the boundary coal–rock pillar, allowing water to migrate inward along bedding planes, joints, primary fractures, mining-induced fractures, and coal seam pores. This process promotes the connection of pre-existing pore–fracture structures and seepage channel formation, weakens particle cementation and structural-plane shear resistance, and reduces the structural integrity, bearing capacity, and water-resisting capacity of the coal–rock pillar. Therefore, the stability deterioration of boundary coal–rock pillars is a continuous process involving channel formation, sustained seepage, strength degradation, enhanced pore–fracture connectivity, permeability enhancement, and further stability reduction.

To address the challenges of water hazard control in the thick water-rich sandstone aquifer of the roof under monoclinal structure conditions at Panel 110504 of Wangwa Coal Mine, as well as the problems of excessive ineffective drainage and high cost associated with the traditional full-face pre-drainage method, a study on the coordinated technology of mining progress and roof water drainage was carried out. By analyzing the geological and hydrogeological conditions of the panel, it was determined that the height of the water-conducting fracture zone reaches 228 m, which has penetrated the Yan’an Formation and entered the sandstone aquifer of the Zhiluo Formation, forming a unified composite water-filling source from the two aquifers. Based on calculations using the Theis equation and field drainage tests, the stable drainage time was determined to be 95 d and the advance drainage distance 300 m. Accordingly, a coordinated technical scheme of “sectional drainage while mining” was proposed, optimizing the layout parameters of drainage boreholes and the division of drainage sections. Field application results show that this technology reduced the average water inflow of the panel by 255.94 m³/h compared with the traditional mode, cumulatively saved 5.1413 million m³ of drainage water, cut drainage costs by 20.5652 million CNY, and no water hazard occurred. The research results can provide a technical reference for mining coal seams with water-rich roof under similar monoclinal structure conditions.