Key Takeaways & Executive Findings
- •• A voussoir beam structure (VBS) model was established to analyze roof stability in gob-side entry retaining (GER), introducing a stability criterion that guides design parameters. • Reducing block B length and immediate roof damage, while increasing coal pillar width, lowers the instability risk of the GER structure. • UDEC simulations revealed that at l=14 m, xb=2.0 m, and water-cement ratio 1.5:1, the coal pillar and backfill body exhibit similar crack damage and maintain stability, achieving better coupling. • Field monitoring confirmed the effectiveness of the CPBB system, with peak stresses of 19.17 MPa (ahead) and 16.14 MPa (behind) in the coal pillar and 12.27 MPa in the backfill body, and floor heave of 380 mm.
Abstract
Gob-side entry retaining (GER) is widely applied in China. Nevertheless, the stability mechanism of the GER with coal pillar-backfill body (CPBB) under dynamic overburden load remains unexplored. A voussoir beam structure (VBS) model is established to analyze roof structure stability during panel advancement, introducing a VBS stability criterion. Reducing block B length l and immediate roof damage variable D, and increasing coal pillar width xc, lowers the GER structure instability risk. Reducing l and the GER width w leads to a CPBB system stability upswing. A UDEC model was established to systematically reveal how the l, backfill body width xb, and strength affect the stability and coupling performance of the CPPB system by monitoring the crack damage DC. Simulation results indicate that at l=14 m, xb=2.0 m, water-cement ratio 1.5:1, the coal pillar and backfill body have similar DC but maintain stability, resulting in CPPB system coupling degree Ϗ, better. A novel GER method supported by the CPBB was implemented on-site. Monitoring results indicated that the coal pillar peak stresses were 19.17 MPa (ahead), 16.14 MPa (behind), and the backfill body peak stress was 12.27 MPa (maximum). The floor heave was 380 mm, with a 103 mm backfill body rib.
1. Introduction
Gob-side entry retaining (GER) serves as a key pillarless extraction strategy in longwall panel mining face (LPMF), providing notable benefits [1,2]. GER generally involves preserving the headgate or tailgate of the preceding LPMF for the next panel, utilizing methods, i.e., roof-cutting with hydraulic fracturing and directional blasting [3] or constructing a backfill body. Moreover, some entries previously developed with coal pillars (Fig. 1a) must be preserved during current LPMF mining by backfill bodies for future mining, as shown in Fig. 1b.
Drawing on scholarly research and field practices [4,5], panel #1 excavation causes block B to fracture and rotate, creating a hinged voussoir beam structure (VBS) [6,7]. As shown in Fig. 1, the backfill body, coal pillar, and gangue collectively support the roof structure. Because of extended service life, maintaining GER with coal pillar and backfill body (GERCB) is more challenging and prone to large deformations.
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ZHANG Dong, ZHU Qiancheng, BAI Jianbiao, WANG Rui, ZHANG Zizheng, FU Hao, LIU Shuaigang, YAN Shuai, GUO Yonghong, TIAN Zhijun, WU Wenda (2025). Theory and simulation investigations on stability control of gob-side entry retaining with coal pillar-backfill body system. SinoTechIntel Verified Research. https://doi.org/10.1016/j.ijmst.2025.07.012
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Frequently Asked Questions
What is gob-side entry retaining (GER) and why is it important?
Gob-side entry retaining (GER) is a pillarless extraction strategy in longwall mining that preserves the headgate or tailgate of the previous panel for use in the next panel. It reduces coal loss and improves resource recovery, making it widely applied in China.
What is the coal pillar-backfill body (CPBB) system?
The CPBB system consists of a coal pillar and a backfill body that together support the roof structure in gob-side entry retaining. It is used to maintain the stability of the entry during and after mining, especially when the entry has a long service life.
How does the voussoir beam structure (VBS) model contribute to stability analysis?
The VBS model analyzes the roof structure stability during panel advancement by considering the hinged blocks of the main roof. It introduces a stability criterion that helps determine optimal design parameters such as block length, coal pillar width, and backfill body dimensions to reduce instability risk.
What were the key findings from the UDEC simulations?
The UDEC simulations showed that at a block length of 14 m, backfill body width of 2.0 m, and water-cement ratio of 1.5:1, the coal pillar and backfill body exhibit similar crack damage and maintain stability, resulting in better coupling performance of the CPBB system.
What were the field monitoring results of the CPBB system?
Field monitoring showed that the coal pillar peak stresses were 19.17 MPa ahead and 16.14 MPa behind, while the backfill body peak stress was 12.27 MPa. The floor heave was 380 mm, and the backfill body rib deformation was 103 mm, indicating the system's effectiveness in controlling entry stability.
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