Effects of gangue particle-size gradation on damage and failure behavior of cemented backfill under uniaxial compression

Abstract

Investigation techniques, such as uniaxial compression tests, acoustic emission, digital image correlation monitoring, and scanning electron microscopy, were used from macroscopic and microscopic perspectives to investigate the effects of gangue particle-size gradation on the damage characteristics of cemented backfill. The peak strength, acoustic emission characteristics, and failure modes of cemented backfills with different gangue size gradations were examined. Test results indicated that with an increase in the gradation coefficient, the compressive strength of the gangue-cemented backfill first increased and then decreased. When the gradation coefficient is 0.5, the maximum compressive strength of the backfill is 4.28 MPa. The acoustic emission counts during the loading of gangue-cemented fills with different gradation coefficients passed through three phases: rising, active, and significantly active. The number of internal pores and cracks, as well as the uneven distribution of their locations, cause differences in acoustic emission characteristics at the same stage and variations in the strength of the backfill due to the different gangue particle-size gradations in the filler sample.

1. Introduction

The solid waste generated by underground mining operations is a source of land use issues, landscape degradation, and environmental pollution [1]. In the context of green development, mining researchers have proposed the green mining concept as a response to the aforementioned issues, and fill-mining technology is an important component of green mining practices [2–8]. Fill mining has been widely used in mining operations due to its substantial economic benefits and capability to notably reduce solid waste pollution [9]. Gangue cement fill mining technology enables the comprehensive utilization of solid coal waste and helps control harmful surface deformation, contributing to the protection of the ecological environment in mining regions. Therefore, this technology is becoming increasingly important for the coal mining industry of China [10–14].

In underground mining, when used as a supporting structure for the roof, the strength of cemented backfill is crucial for the stability of the quarry. The mechanical properties of cemented backfill are notably affected by the type of aggregate and particle size [15–18]. Therefore, the type of aggregate and the particle size of cemented backfill have received considerable attention from the scientific community. Wang et al. [19] tested the filling ratio with gypsum using different crushed stone grain sizes. This test was realized by using the optimal ratio of combined gravel and gypsum-cemented backfill and testing the filling ratio with gypsum using different crushed stone grain sizes. Deng et al. [20] compared the effects of two aggregates with different particle sizes on the strength of cemented backfill. Their results indicated that adding an appropriate amount of coarse aggregates drastically increased the strength of the backfill. Wen et al. [21] optimized the gradation of a mixed aggregate through gradation analysis and controlled the segregation rate of the slurry, using yield stress as the condition. Börgesson et al. [22] believed that the particle size distribution of the aggregate leads to poor homogeneity of the cemented backfill materials, resulting in differences in the mechanical properties of the cemented backfill. Gautam et al. [23] considered aggregate grading to be an important parameter that affects the quality of filling materials. Yang et al. [24] replaced waste rock bars with fly ash for grinding coarse sand aggregates, and their results indicated that the addition of fly ash inhibited strength development in the early stages of backfill but promoted strength growth in the later stages. Kesimal et al. [25] and Fall et al. [26] investigated the effects of aggregate type and content on the strength of the backfill. In addition, Zha et al. [27] and Zhang [28] performed uniaxial compression tests on filling materials and studied the effects of grade on strength and deformability. According to Talbot’s theory, researchers have explored the mechanical properties of backfills with different gradation coefficients and determined the optimal gradation [29–33]. Recently, an increasing number of scientists have examined the effects of t