Mechanical properties, deformation response, energy evolution and failure pattern of stratified cemented tailings backfill under triaxial compression

Abstract

The backfill should keep stable in the primary stope when mining an adjacent secondary stope in subsequent open stoping mining methods, and the large-size mined-out area is usually backfilled by multiple backfilling before the recovery of a secondary stope, resulting in a layered structure of backfill in stope. Therefore, it is significant to investigate the deformation responses and mechanical properties of stratified cemented tailings backfill (SCTB) with different layer structures to remain self-standing as an artificial pillar in the primary stope. The current work examined the effects of enhance layer position (1/3, 1/2, and 2/3) and thickness ratio (0, 0.1, 0.2, and 0.3) on the mechanical properties, deformation, energy evolution, microstructures, and failure modes of SCTB. The results demonstrate that the incorporation of an enhance layer significantly strengthens the deformation and strength of SCTB. Under a confining pressure of 50 kPa, the peak deviatoric stress rises from 525.6 to 560.3, 597.1, and 790.5 kPa as the thickness ratio of enhance layer is increased from 0 to 0.1, 0.2, and 0.3, representing a significant increase of 6.6%, 13.6%, and 50.4%. As the confining pressure increases, the slopes of the curves in the elastic stage become steep, and the plastic phase is extended accordingly. Additionally, the incorporation of the enhance layer significantly improves the energy storage limit of SCTB specimen. As the thickness ratio of the enhance layer increases from 0 to 0.1, 0.2, and 0.3, the elastic energy rises from 0.54 to 0.67, 0.84, and 1.00 MJ·m−3, representing a significant increase of 24.1%, 55.6%, and 85.2%. The internal friction angles and cohesions of the SCTB specimens are higher than those of the CTB specimens, however, the cohesion is more susceptible to enhance layer position and thickness ratio than the internal friction angle. The failure style of the SCTB specimen changes from shear failure to splitting bulging failure and shear bulging failure with the presence of an enhance layer. The crack propagation path is significantly blocked by the enhance layer. The findings are of great significance to the application and stability of the SCTB in subsequent stoping backfilling mines.

1. Introduction

The rapid growth of the mining sector has spurred remarkable economic development in numerous nations. However, this mineral extraction, notably of metallic resources, has also posed numerous challenges, including the management of solid waste and the handling of voids left by underground mining activities [1‒3]. Solid wastes (such as tailings and waste rock) not only occupy a large amount of land resources but also contain harmful substances in some untreated or improperly treated tailings, which pose a serious effect on the environment [4‒5]. In addition, the underground goafs may induce rock bursts and subsidence hazards.

At present, a novel mining technology, cemented tailings backfill (CTB), is adopted in an increasing number of mines around the world. It is commonly composed of cementitious materials, tailings, water, and other mineral or chemical admixtures, which are usually transported into underground goafs or stopes by gravity flow or pump. The CTB not only eliminates the potential collapse hazards but also disposes of a large number of tailings. Therefore, it has become one of the eco-friendly and safe mining technologies lately [6‒7]. The mechanical strength of CTB is crucial for maintaining the stability of the primary stope as mining an adjacent secondary stope in subsequent open stoping mining method, which is mainly gained by hydration reaction from cementitious materials with water. Consequently, the binder cost of CTB accounts for approximately 70% of the total backfill operation costs [8‒10]. Many ways have been employed to improve the strength and decrease the costs of CTB. The mechanical property of CTB is mainly influenced by a combination of external and internal factors, such as cement-to-tailings ratio (c/t), mass concentration, temperature, curing time, and other mineral admixtures. Research by Xu et al. [11‒12] demonstrated that low temperatures impede the strength development of CTB, whereas higher temperatures lead to enhanced strength. Jin et al. [13] investigated the effects of different particle sizes of tailings on the strength of the CTB. It was observed that as the particle size of the tailings increased, the strength and elastic modulus of the CTB first increased and then decreased.