Uniaxial creep tests at 80 MPa with different temperatures and at 600°C with different loads were carried out for a 12%CrMoV martensitic steel. The creep strain behaviour was analysed using an ana lytical expression where. the creep strain rate is proportional to the exponential of the creep strain. The creep curves, rupture times and strains could be well reproduced. The observed and predicted rupture times satisfied the Monkman-Grant relationship.

The gob-side entry layout is popular at two-entry longwall mine sites in China for the benefit of improving the coal recovery rate. Currently, two methods have been widely used to develop gob-side entries, including gob-side entry retaining and gob-side entry driving. Gob-side entry retaining maximizes the recovery rate by pillarless mining but increases the difficulty in gob-side entry support. Also, this method has limited applications in hard roof conditions. The gob-side entry driving mine site uses the rib pillar to separate the gob entry and the gob area of the previous panel, which leads to additional coal losses. The waste is more intolerable in large-cutting-height panels and longwall top coal caving panels as the Chinese government limits the minimum recovery rate of longwall panels using these mining methods. In this paper, a new gob-side entry layout method, termed gob-side pre-backfill driving, is established to overcome the shortcomings of the existing methods. The new method eliminates rib pillar losses and enhances gob-side entry stability. The feasibility of gob-side pre-backfill driving is studied by numerical modelling and a field trial at Changcun Mine in China. The results indicate that gob-side pre-backfill driving is an alternative for gob-side entry development. This method is practical and also has the potential to bring significant economic benefits to the mining industry.

To investigate the fire prevention and suppression characteristics of coal gangue slurry grouting in goafs and the enhanced regulatory mechanisms of additives, the slurry-forming performance of coal gangue slurry was tested. The effects of heating temperature, grouting thickness, and heating duration on the surface temperature distribution characteristics were analyzed. Temperature-programmed experiments were conducted to examine the influence of various additives on the spontaneous combustion propensity of coal gangue, with a comparative analysis of the inhibitory effects between ammonium polyphosphate (APP) and other additives. The results demonstrate that the prepared coal gangue slurry exhibited no segregation or sedimentation, with a plasticity index consistent with standard grouting material requirements, confirming its superior stability. The central, maximum, and minimum surface temperatures of the slurry showed polynomial functional relationships with heating temperature. Surface temperature initially increased and then decreased with grouting thickness, with 10 cm identified as the critical thickness for temperature transition. Overall, the central, maximum, and minimum surface temperatures increased progressively with rising heating temperatures. In addition, under all tested conditions, the average surface temperature remained below 80 °C for slurries with >5 cm grouting thickness, meeting fire prevention requirements. However, the CO and CO₂ concentrations increased significantly as heating temperatures rose from 100 °C to 300 °C. At grouting thicknesses of 9–12 cm, CO and CO₂ emissions occurred only at 300 °C and decreased with increasing thickness. The coal gangue slurry modified with ammonium polyphosphate (APP) additives exhibited optimal antioxidant performance, significantly suppressing CO and CO₂ emissions, which further diminished with higher additive dosages. The findings of this study provide critical insights into the fire prevention performance of coal gangue slurry grouting and the application of additives in this field.

Coal gangue, the primary solid waste generated during the coal mining process, is typically disposed of on the surface, where it gradually accumulates to form gangue piles that significantly contaminate the surrounding environment. Filling technology has been widely employed for the safe and efficient disposal of coal gangue due to its sustainability, safety, and efficiency. However, there is still a lack of theoretical research on the concentration of gangue slurry in long-distance filling pipeline transportation. Therefore, a calculation model of the ultra-long-distance transportable concentration of coal gangue slurry with different grades was constructed based on the static anti-segregation performance and Bingham model. In addition, the relevant parameters of the calculation model of the ultra-long-distance transportable concentration of coal gangue slurry in this mine were determined using the 8 km pipeline transport of coal gangue slurry in one mine as the technical background. It was subsequently demonstrated that the yield stress, plastic viscosity, and mass concentration of the various grades of gangue slurry in this mine exhibit an increasing exponential function, while the slurry density and mass concentration exhibit an increasing linear function, and the mass concentration and actual flow rate correspond to a quadratic polynomial increment. Finally, the minimum and maximum concentrations for different grades of gangue slurry that can be transported over long distances in this mine were determined. This work provides theoretical and practical guidance on how to select the concentration of gangue slurry for long-distance pipeline transport.

To reduce the loss of coal pillars between two adjacent longwall working faces, gob-side pre-backfill driving (GPD) procedure is suggested. This paper introduces in detail the principles and characteristics of the GPD procedure. Based on the arc triangle block (ATB) formed by the fractures of the main roof, the Winkel Elastic Foundation Beam model of the relevant rock strata structure is established and analyzed. The influence of the different breaking positions of the ATB of the main roof, the different geological conditions of the surrounding rock, and the parameters of the backfill body on the stability of the backfill body are analyzed. Also, the adaptability of the GPD procedure under any geological conditions is analyzed. The results show that the sensitivity of the aforementioned factors on the stability of the backfill from high to low is as follows: the thickness of the immediate roof, the elastic modulus of the main roof, the elastic modulus of the immediate roof, the thickness of the main roof, the thickness of the coal seam, the elastic modulus of the coal seam, the width of the backfill body, the buried depth, and the elastic modulus of the backfill body. According to the geological conditions of the Changcun Mine, it can be determined that if the fracture location of ATB of the main roof from the backfill is less than 5 m, the GPD procedure cannot be adopted. For this situation, the required strength of the backfill is high; the backfill is difficult to maintain, and it is prone to fracture failure. The GPD procedure cannot be used for all geological conditions. Before the GPD procedure is implemented, a pre-judgment must be made not to cause unnecessary losses.