Zexin Li

To address the difficulty of roof control in longwall paste backfill mining and to better capture the backfill’s ‘sequential bearing’ effect, this study proposes an elastic foundation beam model. Based on the Gaohe Coal Mine, the “coal-support-backfill” model incorporates the time-varying characteristics of paste materials. Analytical solutions for roof deflection and bending moment were derived to reveal the spatiotemporal evolutionary laws of key parameters on roof stability. Results show the filling rate is the most sensitive factor controlling ultimate roof subsidence, directly determining the roof’s actual suspended span and breaking risk. The final-set strength limits long-term deformation but exhibits a marginal diminishing effect. Conversely, early strength dominates the initial subsidence rate, preventing excessive early deformation. Additionally, increasing the filling step distance significantly increases overall subsidence, whereas support resistance improves the initial bending moment distribution. Ultimately, surrounding rock control in paste backfill stopes is a dynamic coupling of “spatial support synergy” and “temporal strength matching” providing a theoretical basis for optimizing mining safety, economy, and efficiency, which ultimately fosters sustainable green mining practices.

To address the support challenges of deep high-stress roadways in coal mines, this study investigates fracture propagation in floor mudstone from the Shanxi Gucheng Coal Mine using the Holmquist-Johnson–Cook constitutive model. Based on laboratory mechanical tests and theoretical calculations, a comprehensive set of HJC model parameters for mudstone was systematically determined. A two-dimensional radial decoupled charge model was developed in LS-DYNA using an Arbitrary Lagrangian–Eulerian fluid–solid coupling algorithm to simulate the loosening blasting process. The results indicate that while the original HJC model’s damage variable effectively captures the formation of the crushed zone, it severely underestimates tensile crack extension, predicting a maximum crack length of merely 25.5 cm. To overcome this limitation, the model was optimized by incorporating supplemental failure criteria for shear strain and tensile stress. The enhanced model successfully reproduced the entire radial fracture propagation process, capturing an extensive fractured zone radius of 205 cm. Crucially, field borehole peeping verified these findings, revealing macroscopic radial fractures extending approximately 1.9 m, which is basically consistent with the simulation results. This study accurately elucidates the dynamic damage mechanisms of mudstone and provides a robust theoretical basis for engineering parameter designs, such as the 4 m borehole row spacing implemented for effective floor pressure-relief blasting.

Paste backfill strength exhibits obvious time-dependent growth, which directly determines the supporting effect and parameter design in longwall backfilling mining. To optimize key parameters for roof stability and surface protection, this study carried out laboratory tests, numerical simulations, and field validation on the E1302-B working face in Gaohe Coal Mine. Results show that the strength of paste backfill increases logarithmically with curing age. The optimal backfilling step distance is 2.4 m, the recommended final cured strength is 4.01 MPa with significant marginal effects, and the backfilling ratio should be no less than 92% to meet Grade-I surface protection requirements. Field applications demonstrate that under these parameters, roof deformation is controllable without fracture, and all surface deformation indexes are within 50% of the standard limits. This work provides a reliable method and practical guidance for parameter optimization in longwall paste backfilling mining.

Longwall paste backfilling mining is a core sustainable green mining technology for coal resources under buildings, railways and water bodies (BRW), yet its large-scale application is severely restricted by the sequential mining–isolation–backfilling–curing operation mode that causes low production efficiency and poor economic feasibility, which hinders the sustainable exploitation of BRW coal reserves and the ecological protection of mining areas. Taking the E1302-B paste backfilling face of Gaohe Coal Mine as the engineering background, this study systematically identified the key efficiency-restricting factors considering the face’s complex geological conditions (maximum roof–floor undulation 300 mm, 72.6% of roof–floor dip angle >1° and irregular cross-section), including low isolation efficiency, cumbersome backfilling process, prolonged paste curing time and insufficient system operation controllability. Technological innovations were carried out from four core dimensions: high-efficiency isolation, high-efficiency backfilling, accelerated curing and intelligent safety control, and a high-efficiency integrated technology system for longwall paste backfilling mining was thus formed, which realizes the synergistic improvement of mining efficiency, economic benefits and sustainability performance. Industrial test validation demonstrated that the technical system significantly boosts the efficiency of isolation, backfilling and solidification in the backfill mining cycle, cutting the time of a single backfill mining operation cycle by 57%. The annual production capacity of the E1302-B face was increased to 0.81 Mt, with a comprehensive backfilling mining cost of 466.63 CNY/t, an annual economic benefit of 108.03 million CNY and a static investment return rate of 48.96%. The E1306 face achieved an even higher annual production capacity of 1.12 Mt with a static investment return rate of 74.94%. This technology system effectively breaks the efficiency and economic bottlenecks of traditional longwall paste backfilling mining, realizes the dual improvement of backfilling mining efficiency and economic benefits, and further releases the ecological, resource and economic sustainability value of paste backfilling mining. It provides technical support and practical approaches for the large-scale application of longwall paste backfilling mining, and lays a solid foundation for the sustainable development of the coal industry under the dual-carbon goal, especially for the balanced development of coal resource exploitation and mining area ecological protection.

Longwall paste backfilling mining is severely restricted in large-scale application due to its sequential mining-isolation-backfilling-curing operation mode, which leads to low production efficiency and poor economic feasibility. Taking the E1302-B paste backfilling face of Gaohe Coal Mine as the engineering background, this study systematically identified the key efficiency-restricting factors including low isolation efficiency, cumbersome backfilling process, prolonged paste curing time and insufficient system operation controllability, in view of the complex geological conditions of the face such as severe undulation of roof and floor and irregular cross-section. Technological innovations were carried out from four core dimensions: high-efficiency isolation, high-efficiency backfilling, accelerated curing and intelligent safety control. A self-adaptive mechanized isolation device was developed, a high-efficiency backfilling process with simplified isolation procedures was proposed, the optimal accelerator addition method with cross-blade mixing was determined, and an integrated intelligent monitoring system covering the whole process of equipment-pipeline-support was constructed. Eventually, a high-efficiency integrated technology system for longwall paste backfilling mining was formed. Industrial test validation demonstrated that the technical system significantly boosts the efficiency of isolation, backfilling and solidification in the backfill mining cycle, cutting the time of a single backfill mining operation cycle by 57%. The annual production capacity of the E1302-B face was increased to 0.81 Mt, with a comprehensive backfilling mining cost of 466.63 CNY/t, an annual economic benefit of 108.03 million CNY and a static investment return rate of 48.96%. The E1306 face achieved an even higher annual production capacity of 1.12 Mt with a static investment return rate of 74.94%. This technology system effectively breaks the efficiency and economic bottlenecks of traditional longwall paste backfilling mining, realizes the dual improvement of backfilling mining efficiency and economic benefits, and provides technical support and practical approaches for the large-scale application of longwall paste backfilling mining.