Compared to traditional long-wall mining, the gob-side entry retaining by roof-cutting (GERRC) technology reduces the amount of entry excavation by 50%, and recovers the previously wasted coal pillar resources, which has obvious superiority in mining efficiency and economic benefits. In response to the problem of reasonable entry location of the GERRC in close-distance coal seams, this paper takes the 9105 Working face in Longmenta Coal Mine as the engineering background and conducts an in-depth study by using methods such as theoretical analysis, numerical simulation and field tests. Firstly, the structural characteristics of the overburden rock for GERRC in the close-distance coal seam are analyzed, based on which a method for determining the reasonable location of the GERRC in close-distance coal seams is proposed; secondly, a mechanical model for load transfer and rock mass damage of the upper coal seam floor was established to analyze the floor damage characteristics and stress distribution law, forming the theoretical analysis of the reasonable entry location; Finally, the optimal entry location (22.5 m from the center of the upper remaining coal pillar) was used for field test of GERRC at the 9105 Working face of Longmenta Coal Mine. It has achieved good on-site application results.

Severe deformation of surrounding rock and excess-gas are the main problems faced in mining of high-gas coal seam. This paper analyzes the deformation characteristics and mechanical model of surrounding rock in high-gas coal seam, and proposes the control technology of surrounding rock deformation and gas prevention and control. Based on this, the entry automatically formed by roof cutting (EAFRC) surrounding rock control technology and constant resistance large deformation anchor cable (CRLDA) support control technology in Shaqu coal mine are put forward. At the same time, the surrounding rock stress and gas migration law of the working face under traditional mining method and EAFRC mining were compared and analyzed. Through the field engineering test, the monitoring and analysis of surrounding rock deformation and gas concentration, the average surrounding rock deformation of roof cutting roadway is 310 mm, and the gas concentration of retained roadway by roof cutting is 0.31%. Through the research in this paper, the surrounding rock stability and gas control of the working face have been realized, and the non-pillar mining of EAFRC has ensured the safe mining of high gas working faces, which provides a reference for the mining of similar mines in non-pillar mining. At the same time, the technical system of EAFRC in non-pillar mining was established, which promoted the development and application of non-pillar mining.

The propagation behavior of hydraulic fractures in deep hard roofs is governed by the multi-factor coupling of injection rate, in situ stress, and fluid viscosity. Taking the Cuimu coal mine as the engineering background, this study systematically investigates the effects of injection rate, lateral pressure coefficient, and fluid viscosity on fracture propagation through numerical simulation. Theoretical derivations based on the KGD (Kristianovich-Geertsma-de Klerk) model are further integrated and validated by field tests. The results indicate a critical injection rate of 6 × 10⁻⁸ m³/s, above which the marginal increase in acoustic emission events declines significantly. Increasing the lateral pressure coefficient from 1.0 to 3.5 shifts the fracture pattern from relatively simple to increasingly complex and interwoven, accompanied by a logarithmic increase in fractal dimension from 1.38 to 1.80. The total acoustic emission count rises to a peak of 125,910 as viscosity increases from 0.001 Pa·s to 0.5 Pa·s, then drops to 44,061 at 1.0 Pa·s, showing a unimodal trend. Theoretical analysis shows that during the propagation stage, the fracture length follows $L\propto Q^{1/2}$, and the maximum fracture opening follows $w_{\max }\propto Q^{1/3}$. The lateral pressure coefficient controls the complexity of the fracture network through the directional distribution of stress intensity factors. Field tests at the Cuimu coal mine adopted a combination of stepwise injection rate and low-viscosity fluid, together with borehole densification and interval-skipping fracturing sequences. The effective fracturing radius reached 25~30 m, roof convergence was reduced by 31%, and the proportion of high-energy microseismic events decreased from 12% to 4%. This study establishes a complete theoretical framework from initiation theory to propagation dynamics and then to multi-crack competition, providing both a theoretical basis and engineering example for optimizing fracturing parameters in hard roofs under high stress anisotropy.

The high stress environment and hard roof conditions seriously limit the application of gob-side roadway retaining. To achieve non-coal pillar mining, this study proposes a novel method combining roadside filling and roof cutting under stress-release and strong support synergy. Mechanical modeling reveals surrounding rock failure mechanisms in high-stress gob-side roadway retaining. Numerical simulations show the new method reduces surrounding rock stress/displacement more effectively than conventional gob-side roadway retaining. Optimized parameters were validated via field tests, confirming significant control of rock deformation under complex high-stress conditions. The method successfully enables non-coal pillar mining, providing a scientific basis for similar applications.

The rapid development of transportation infrastructure in challenging geological regions necessitates innovative tunneling methods that balance efficiency, safety, and cost. This study addresses the critical construction bottleneck of large-span soft rock tunnels under high ground stress, where conventional methods often lead to unacceptable delays. Focusing on a 24.53 m span railway tunnel in southwest China, we present the significant engineering application of a “pilot-tunnel-first” method as a strategic solution to stringent schedule pressures. The core innovation lies not only in the adoption of a large 13.2 m wide pilot tunnel but also in a synergistically enhanced support system, featuring elongated bolts (6 m and 12 m) and strengthened steel arches. Numerical simulations and field validation confirmed that this optimized approach achieves a stability comparable to the traditional double-side drift method while dramatically accelerating progress. The successful implementation shortened the construction period by 1.96 months for a key 123 m section, with a manageable cost increase of approximately Chinese Yuan (CNY) 782,000, thereby ensuring the timely opening of the entire tunnel. The primary significance of this research is to provide a proven and practical technical strategy for overcoming similar soft rock tunneling challenges where project timelines are paramount, offering a substantial value for the design and construction of modern infrastructure under complex constraints.

This study investigates the influence of shallow water-bearing sand layers on surface subsidence characteristics in coal mining areas with thick loose strata, with the ultimate goal of contributing to sustainable environmental protection. Firstly, a numerical simulation test was designed to analyze and study the influence of the loose layer thickness, mining height, bedrock slope, and sand inclusion on the surface movement and deformation characteristics. Secondly, the mechanical model of seepage flow in the sand layer was established to study the influence mechanism of the internal stress distribution of the sand layer and the seepage of the water body after mining on the surface subsidence. Finally, by studying the law of surface subsidence corresponding to the mining of 3205 working face in a mine, it was found that mining caused the partial overlying soil layer to move integrally and generate a large displacement difference with the adjacent layer, which verifies the conclusions of numerical simulation and mechanical analysis. The results of the study show that the thickness of the loose layer is the main control factor that causes the surface subsidence range and the building damage to increase; the shallow water-bearing sand-bearing layer has two types of movements: displacement and flow. The critical hydraulic slope has not reached the sand. The layer has a linearly increasing horizontal displacement value in the thickness direction; when the critical hydraulic slope is reached, the sand layer cannot transmit the frictional force, causing the overlying soil layer to slide as a whole. Both forms are prone to tensile damage on the surface. The research results provide a theoretical basis and practical case for surface subsidence reduction and green mining under similar geological conditions.