Key Takeaways & Executive Findings
- •• A semi-theoretical method for deriving roof characteristic curves in room-and-pillar mining was proposed and validated against laboratory similar tests, showing good agreement. • Pre-stressed expandable props outperform natural pillars and concrete props as yielding supports, effectively controlling roof deformation and preventing collapse. • The weakening factor for the plastic zone in the roof characteristic curve was estimated at 0.75, providing a quantitative basis for support design. • The study offers practical insights for optimizing support strategies, enhancing safety and efficiency in room-and-pillar mining operations.
Abstract
This study is to determine the support mechanism of pre-stressed expandable props for the stope roof in room-and-pillar mining, which is crucial for maintaining stability and preventing roof collapse in mines. Utilizing an engineering case from a gold mine in Dandong, China, a laboratory-based similar test is conducted to extract the actual roof characteristic curve. This test continues until the mining stope collapses due to a U-shaped failure. Concurrently, a semi-theoretical method for obtaining the roof characteristic curve is proposed and verified against the actual curve. The semi-theoretical method calculated that the support force and vertical displacement at the demarcation point between the elastic and plastic zones of the roof characteristic curve are 5.0 MPa and 8.20 mm, respectively, corroborating well with the laboratory-based similar test results of 0.22 MPa and 0.730 mm. The weakening factor for the plastic zone in the roof characteristic curve was semi-theoretically estimated to be 0.75. The intersection between the actual roof characteristic curve and the support characteristic curves of expandable props, natural pillars, and concrete props indicates that the expandable prop is the most effective “yielding support” for the stope roof in room-and-pillar mining. That is, the deformation and failure of the stope roof can be effectively controlled with proper release of roof stress. This study provides practical insights for optimizing support strategies in room-and-pillar mining, enhancing the safety and efficiency of mining operations.
1. Introduction
The interaction between supporting elements and the stope roof forms the basis for optimizing support parameters in room-and-pillar mining. This interaction can be quantified through the intersection of the roof and support characteristic curves. The roof characteristic curve illustrates the relationship between the support forces and the vertical displacement of the stope roof. It is theoretically possible to calculate the deformations of a homogeneous and isotropic rock mass under hydrostatic pressure around a circular excavation, considering different support forces and far-field stresses [1−3]. However, deriving the deformations of a heterogeneous and anisotropic rock mass around a non-circular excavation is challenging. Therefore, the complex variable function method is employed to calculate the deformations of the rock mass at key feature points around the excavations, in order to obtain the roof characteristic curve.
GAO et al [4] developed an analytical solution for deformation in the rock mass surrounding a rectangular excavation, where the far-field stresses are equal in vertical and horizontal directions. EXADAKTYLOS et al [5] obtained the deformations of the rock mass around a semicircular excavation, while TAN et al [6] obtained the deformations of the rock mass for a horseshoe-shaped excavation. KANG [7] derived an analytical solution for the deformations of a rectangular plate containing a circular hole, considering the presence of linearly varying far-field stresses. LEI et al [8], and NG et al [9] presented an analytical solution for the deformation of the rock mass surrounding a rectangular excavation under inclined far-field stress. KONG et al [10] derived an analytical solution for the elastic deformation of the rock mass surrounding a double-tunnel excavation. Currently, theoretical analytical solutions for the deformation of rock masses primarily address non-circular excavations, variations or inclinations in far-field stresses, and multiple excavations.
Deformations of the rock mass around the excavation, under various support forces, can be obtained more flexibly and conveniently for the roof characteristic curve using numerical simulation compared to theoretical analysis. YAVUZ [11] estimated the roof characteristic curves for circular, arched, and rectangular excavations under hydrostatic pressure using the finite difference method (FDM) [12]. PRUSEK et al [13] determined the roof characteristic curve for the longwall mining using the Phase2 method. It is
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LI Kun-meng, WANG Yong-jiang, LIU Kai, LI Yuan-hui, FU Zheng-chun, PANG Bo-xue (2025). Determination of support mechanical mechanism of pre-stressed expandable props to stope roof in room-and-pillar mining. Journal of Central South University. https://doi.org/10.1007/s11771-025-6058-4
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Frequently Asked Questions
What is the main purpose of this study?
The study aims to determine the support mechanical mechanism of pre-stressed expandable props for the stope roof in room-and-pillar mining, which is crucial for maintaining stability and preventing roof collapse.
How was the roof characteristic curve obtained?
The roof characteristic curve was obtained through laboratory-based similar tests and a semi-theoretical method using complex variable function, which were verified against each other.
What are the key findings regarding expandable props?
Expandable props were found to be the most effective 'yielding support' compared to natural pillars and concrete props, as they allow controlled roof deformation and stress release, enhancing stability.
What is the significance of the weakening factor?
The weakening factor for the plastic zone in the roof characteristic curve was estimated to be 0.75, which is important for predicting roof behavior and designing support systems.
How can this research benefit mining operations?
The research provides practical insights for optimizing support strategies in room-and-pillar mining, leading to improved safety and efficiency by preventing roof collapse and reducing support costs.
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