Key Takeaways & Executive Findings
- •• Principal stress rotation is most pronounced at the ends of the coal seam goaf, with maximum rotations of 19° (clockwise) and −40° (counterclockwise) in the bauxite layer. • Inclined bauxite pillars experience combined compressive and shear loading; clockwise principal stress rotation increases the shear-to-normal stress ratio, reducing pillar stability. • Pillars beneath the coal wall fail first due to stress concentration and principal stress rotation, potentially triggering cascading instability among adjacent pillars. • The study provides a theoretical basis and practical guidance for safe co-mining of coal seams and bauxite resources.
Abstract
The “upper coal and lower bauxite” resource distribution pattern is widespread in China, where mining of the overlying coal seam significantly alters the stress environment of the underlying bauxite layer. This study investigates the stability of inclined bauxite pillars under the influence of stress redistribution caused by coal seam extraction. A theoretical model is developed to calculate the direction and magnitude of principal stresses in the inclined floor strata, and a pillar stability analysis model is established that considers the effect of principal stress rotation. The research employs a combination of theoretical analysis, physical modeling, numerical simulation, and field observation. Findings indicate that stress rotation is most pronounced at both ends of the coal seam goaf, with the maximum clockwise and counterclockwise rotation angles of 19° and −40°, respectively, observed in the bauxite layer. Inclined bauxite pillars are subjected to combined compressive and shear loading. Under such conditions, clockwise rotation of principal stress increases the shear-to-normal stress ratio, thereby reducing pillar stability. Pillars located beneath the coal wall are the first to fail due to stress concentration and principal stress rotation, which can trigger a cascade of instability among the adjacent pillars. The findings provide a theoretical basis and practical guidance for ensuring the safe co-mining of coal seams and bauxite resources.
1. Introduction
In China, numerous coal seams and associated mineral deposits exhibit significant vertical overlap [1]. A prominent example is bauxite, a typical sedimentary mineral resource formed primarily during the Carboniferous and Permian periods. This epoch also coincided with the peak formation rate and volume of coal in geological history [2], resulting in a common stratigraphic configuration known as “upper coal and lower bauxite” [3, 4]. As the global leader in alumina production, China accounted for approximately 52.2% of the world's output in 2020 [5]. With rising alumina demand, the need to develop bauxite resources beneath previously mined coal seams has become increasingly urgent.
Bauxite is typically extracted using strip mining [6], where uniformly spaced pillars are left to support the overburden. In co-mining scenarios, however, stresses induced by coal seam extraction can significantly impact the stability of these pillars. Damage to pillars may trigger geohazards such as rock bursts [7], pillar chain failure [8], overburden collapse [9], and water or gas inrushes [10, 11]. These hazards are directly related to the stress environment and pillar integrity. Therefore, it is essential to investigate the stress distribution within the coal seam floor and evaluate the effects of uneven mining-induced stresses on the stability of underlying bauxite pillars. Such research is essential for understanding pillar failure mechanisms and promoting the safe and efficient development of bauxite resources within coal-bearing strata.
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LIU Wang, YANG Yu-gui, CHEN Yong, HUANG Bing-xiang, CAI Cheng-zheng, SHANG Run-peng, QIU Chao (2025). Stability analysis of inclined bauxite pillar under goaf of coal seam considering principal stress rotation. Journal of Central South University. https://doi.org/10.1007/s11771-025-6119-8
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Frequently Asked Questions
What is the main focus of this study?
The study focuses on the stability of inclined bauxite pillars under the influence of stress redistribution caused by coal seam extraction, specifically considering the effect of principal stress rotation.
What methods were used in this research?
The research employs a combination of theoretical analysis, physical modeling, numerical simulation, and field observation.
What are the key findings regarding principal stress rotation?
Stress rotation is most pronounced at both ends of the coal seam goaf, with maximum clockwise and counterclockwise rotation angles of 19° and −40°, respectively, observed in the bauxite layer.
How does principal stress rotation affect pillar stability?
Clockwise rotation of principal stress increases the shear-to-normal stress ratio, thereby reducing pillar stability.
What is the practical significance of this study?
The findings provide a theoretical basis and practical guidance for ensuring the safe co-mining of coal seams and bauxite resources.
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