Mechanical response and impact tendency index correction of gangue-coal combined structure

Abstract

To investigate the mechanical response during failure and the impact tendency characteristics of gangue-coal combined structure, uniaxial compression tests were conducted on nine groups of combined structures, each with varying gangue thicknesses and positions. The response patterns of compressive strength, elastic modulus, pre-peak accumulated energy, elastic energy index, and impact energy index were systematically analyzed. Furthermore, a new index for evaluating the impact tendency of gangue-containing coal was proposed, and its effectiveness was verified. The findings are as follows: (1) As the gangue thickness increases, both the compressive strength and the pre-peak energy of the combined structure decrease, whereas the elastic modulus increases accordingly. When the gangue is located in the lower-middle position, the combined structure exhibits the lowest compressive strength and elastic modulus but the highest pre-peak energy. (2) As the gangue shifts toward the middle position of the combined structure, the failure mode gradually transitions from complete "crushing" failure to an incomplete "point-type" failure. As gangue thickness further increases, the failure region evolves from overall failure to localized failure, with the degree of failure shifting from complete to incomplete. The Kcrc value corresponding to "crushing" complete failure is higher and has a stronger impact tendency compared to "point-type" incomplete failure. (3) The proposed comprehensive impact instability evaluation index Kcrc for the gangue-coal combined structure has shown a significant positive correlation with compressive strength (Rc) and impact energy index (KE), further verifying its rationality in comprehensively assessing the impact tendency of gangue-containing coal bodies. Applying this index to the evaluation of gangue-containing coal seams provides a more accurate reflection of their impact tendency compared with the residual energy index, which has a wide range of potential applications and practical significance.

1. Introduction

With the progressive depletion of shallow coal resources in China, deep-mining operations have gradually become standard practice. As mining depth increases, geological conditions within mines become increasingly complex, and rockburst has emerged as one of the primary hazards threatening mine safety and production [1, 2]. Coal-containing strata are composed of various alternating coal seams and rock strata, with a complex depositional environment, and gangue layers are commonly found in most coal seams. Under certain mining-induced disturbances, a large amount of energy accumulated in the coal-rock system may be suddenly released, triggering rockburst disasters [3−5]. The presence of gangue within coal seams is a common phenomenon in engineering practice. Focusing solely on the mechanical properties of single coal specimens is not comprehensive and fails to reflect actual engineering conditions. Therefore, it is significant to investigate the mechanical characteristics, failure mechanisms, and impact effects of gangue-coal combined structures.

Extensive research on coal-rock combined structures has been conducted by scholars both domestically and internationally. CHEN et al [6] analyzed the mechanical properties of coal-rock combined structures with varying coal-rock ratios and configurations, focusing on parameters such as compressive strength, elastic modulus, pre-peak energy, and impact energy index. ZUO et al [7, 8] investigated the strength, deformation, and failure characteristics of coal-rock interfaces at different inclination angles through uniaxial and triaxial tests. ZHANG et al [9], LIU et al [10], and FENG et al [11] studied the damage patterns and failure types of coal-rock assemblages under uniaxial and triaxial conditions, as well as the mechanical and acoustic emission properties of deep marble under real triaxial perturbation compression. Their work revealed the relationship between perturbation load and intermediate principal stresses under low strain rates. FENG et al [12] established a statistical damage constitutive model for deep rocks. ZHAO et al