Key Takeaways & Executive Findings
- •• Flexible passive confining pressure induces three distinct compression stages in granular backfill materials, differing from traditional rigid confinement. • AE signals show bimodal energy distribution with time intervals varying by over 4 times, indicating a transition from shear to tensile failure modes. • Lateral confinement stiffness significantly enhances axial bearing capacity; at 30% axial strain, rigid confinement yields nearly 5 times higher axial stress than flexible confinement. • Fractal dimension of particle breakage increases from 1.94 to 2.39 with rising confinement stiffness, reflecting enhanced particle fragmentation.
Abstract
To address the deviation between rigid confining pressure experiments and actual engineering conditions of deep backfill mining, where backfill near the working face has less confining pressure, while that in deep goaf areas is under high confining pressure, this study investigates the load-bearing characteristics of rock granular materials under flexible passive confining pressure. Customized PC molds with varying wall thicknesses and rigid steel molds were used to construct a gradient confining pressure environment. Compression tests were conducted, combined with the characterization of acoustic emission (AE) monitoring, strain measurement, particle sieving, and scanning electron microscopy (SEM) observation. The results show that flexible passive confining pressure divides the particle compression process into three stages that are different from those under traditional rigid constraints, namely the initial compaction stage, the crushing failure stage, and the lateral confinement-dominated stage. AE signals exhibit a bimodal energy distribution, and the time interval between the two can vary by more than 4 times with changes. The failure modes transition from shear to tension. Compared with intact materials, granular materials under lateral confinement maintain continuous volume contraction, and can even maintain a continuous volume contraction trend at least when the strain reaches 8%. And lateral confinement stiffness significantly enhances axial bearing capacity: when the axial strain reaches 30%, the axial stress in the rigid confinement group is nearly 5 times that in the flexible confinement group. Fractal dimension increases from 1.94 to 2.39 as the confinement stiffness rises. This study clarifies the influence mechanism of lateral confinement stiffness on granular mechanics, providing fundamental support for optimizing backfill design based on goaf locations and improving surrounding rock control in deep green mining.
1. Introduction
As the primary energy source in China, coal has long occupied a dominant position in the country's primary energy structure, and no fundamental change in this status is likely to occur in the short term [1]. Problems like surface subsidence, drastic mine pressure, and groundwater loss—all caused by the associated high-intensity mining—are worsening progressively, putting the sustainable development and ecological security of mining areas at risk [2]. At present, backfill mining encompasses a variety of types, including solid, paste, and ultra-high water backfilling. Solid backfilling, in particular, sees extensive use in mining projects, thanks to its advantages of abundant material sources, low cost, and uncomplicated process [3].
In the research of rock stratum control via backfilling mining, numerous scholars have conducted extensive explorations focusing on the interaction mechanism between backfill and surrounding rock, the law of rock stratum movement, and control effects, resulting in a wealth of theoretical and technological achievements. In early studies, through theoretical analysis and on-site monitoring, Miao et al. [4] established the equivalent mining height method.
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JU Minghe, ZHANG Bo, YU Liyuan, HU Chaohan, LI Baiyi, GU Wenzhe, DOU Linming, ZHANG Qiang, JI Hao, CHENG Ruyi (2026). Load-bearing characteristics of backfilling solids in deep mining under flexible passive confining pressure: An experimental study. SinoTechIntel Verified Research. https://doi.org/10.1016/j.ijmst.2026.01.002
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Frequently Asked Questions
What is the main objective of this study?
The study aims to investigate the load-bearing characteristics of rock granular materials under flexible passive confining pressure, addressing the deviation between rigid confining pressure experiments and actual deep backfill mining conditions.
How was the flexible passive confining pressure simulated in the experiments?
Customized PC molds with varying wall thicknesses and rigid steel molds were used to create a gradient confining pressure environment, allowing for the simulation of different confinement stiffness conditions.
What are the three stages of particle compression under flexible passive confining pressure?
The three stages are the initial compaction stage, the crushing failure stage, and the lateral confinement-dominated stage, which differ from those under traditional rigid constraints.
How does lateral confinement stiffness affect axial bearing capacity?
Lateral confinement stiffness significantly enhances axial bearing capacity; at 30% axial strain, the axial stress in the rigid confinement group is nearly 5 times that in the flexible confinement group.
What is the significance of the fractal dimension in this study?
The fractal dimension increases from 1.94 to 2.39 as confinement stiffness rises, indicating enhanced particle breakage and providing a quantitative measure of the fragmentation degree.
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