Key Takeaways & Executive Findings
- •• A novel method combining gob-side entry driving (GSED) and directional roof-cutting enables efficient recovery of coal pillars under thick-hard roofs, improving resource recovery and safety. • Optimal narrow coal pillar width (10 m) and working face length (65 m) were determined via theoretical analysis and numerical simulation, validated by field application. • Pre-splitting of 8.2 m thick-hard roof using directional drilling and energy-gathering blasting ensures symmetrical roof collapse and reduces mine pressure hazards. • Field observations confirm the effectiveness of the integrated approach, offering a practical reference for similar mining conditions.
Abstract
To enhance the recuperation rate of the mine and comply with the stipulations of green mining technology, it is vital to expeditiously recuperate the coal pillar resources in the final stage, thus preventing the considerable squandering of resources. The coal pillar resource of the main roadway and its branch roadway constitutes a significant recovery subject. Its coal pillar shape is regular and possesses a considerable strike distance, facilitating the arrangement of the coal pillar recovery working face (CPRWF) for mining operations. However, for the remaining coal pillars with a thick and hard roof (THF) and multiple tectonic zones, CPRWF encounters challenges in selecting an appropriate layout, managing excessive roof pressure, and predicting mining stress. Aiming at the roadway coal pillar group with THF and multi-structural areas in specific projects, a method of constructing multi-stage CPRWF by one side gob-side entry driving (GSED) and one side roadway reusing is proposed. Through theoretical calculation of roof fracture and numerical simulation verification, combined with field engineering experience and economic analysis, the width of the narrow coal pillar (NCP) in the GSED is determined to be 10 m and the length of the CPRWF is 65 m. Concurrently, the potential safety hazard that the roof will fall asymmetrically and THF is difficult to break during CPRWF mining after GSED is analyzed and verified. Then, a control method involving the pre-cutting of the roof in the reused roadway before mining is proposed. This method has been shown to facilitate the complete collapse of THF, reduce the degree of mine pressure, and facilitate the symmetrical breaking of the roof. Accordingly, a roof-cutting scheme based on a directional drilling rig, bidirectional shaped polyvinyl chloride (PVC) pipe, and emulsion explosive was devised, and the pre-splitting of 8.2 m THF was accomplished. Field observations indicate that directional cracks are evident in the roof, the coal wall is flat during CPRWF mining, and the overall level of mining pressure is within the control range. Therefore, the combined application of GSED and roof-cutting technology for coal pillar recovery has been successfully implemented, thereby providing new insights and engineering references for the construction and pressure relief mining of CPRWF.
1. Introduction
In underground coal mining, a substantial number of security coal pillars are frequently set up for the development roadways, such as main roadways [1−3]. When the mine is mined to the end of the whole life cycle, to improve the recovery rate of the mine and avoid the waste of resources, it is necessary to recover the coal pillar resources in time. The traditional room-and-pillar and strip recovery methods are often used, but the recovery rate of such methods is low [4, 5]. For the recovery of coal pillars in main roadway, due to its long distance, the traditional coal pillar recovery method will cause a lot of waste. It is structurally suitable for the recovery of long wall working face, that is, coal pillar recovery working face (CPRWF) [6, 7]. Furthermore, given that the main roadway is adequately supported, and ventilation is unimpeded, which can be directly reused as a mining roadway.
However, in practice, there are often branch roadways of the main roadway, which occupy a significant number of coal pillars and have a narrow spacing, rendering reuse of the roadway impractical. In such instances, it is necessary to re-excavate the roadway to establish CPRWF [8−10]. Therefore, the coal pillar recovery of the main roadway and its branch roadway can be arranged by reusing the roadway, re-excavating the roadway, and combining the two to arrange CPRWF for recovery, as shown in Figure 1. The various types of CPRWF should be rationally arranged based on the actual conditions on the site.
The method of forming CPRWF through roadway excavation has the potential to recover a greater quantity of coal resources, which would yield significant economic benefits. The design of narrow coal pillar (NCP) retention should be performed in advance on the side of the excavated face [11]. NCP has the potential to enha
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WU Yi-yi, YE Qiu-cheng, GAO Yu-bing, ZHANG Xing-xing, HE Man-chao (2025). Innovative pillar recovery method integrating gob-side entry driving and directional roof-cutting for thick-hard roof coal seams. Journal of Central South University. https://doi.org/10.1007/s11771-025-6060-x
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Frequently Asked Questions
What is the main challenge in recovering coal pillars under thick-hard roofs?
The main challenges include selecting an appropriate layout for the coal pillar recovery working face, managing excessive roof pressure, and predicting mining stress, especially in areas with multiple tectonic zones.
How does the proposed method improve coal pillar recovery?
The method integrates gob-side entry driving (GSED) and directional roof-cutting, which allows for efficient recovery of coal pillars while ensuring roof stability and reducing mining pressure hazards.
What are the key parameters determined in the study?
The study determined that the optimal narrow coal pillar width is 10 m and the length of the coal pillar recovery working face is 65 m, based on theoretical calculation and numerical simulation.
How is the thick-hard roof managed during mining?
A roof-cutting scheme using directional drilling, bidirectional shaped PVC pipes, and emulsion explosives is employed to pre-split the roof, facilitating its complete collapse and symmetrical breaking.
What are the field results of applying this method?
Field observations show that directional cracks are evident in the roof, the coal wall remains flat during mining, and the overall mining pressure is within the control range, confirming the method's effectiveness.
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