Search Results (9)

Due to the poor stability of the roof and floor of the roadway in the 3-1 coal seam of Chahasu Coal Mine, traditional gob-side entry retaining (GER) methods fail to meet the production safety requirements. To address this, a GER technology using paste backfill was proposed. This study reveals the stability mechanism of the surrounding rock in GER with paste backfill through theoretical analysis, numerical simulation, and industrial experiments. First, theoretical analysis was conducted to determine the overburden movement characteristics under varying backfill ratios. Uniaxial compressive tests on the paste material demonstrated that its bearing capacity reaches a relatively stable state after 14–28 days of curing. Second, numerical simulations were performed to study the deformation patterns of the surrounding rock and mine pressure characteristics under backfill ratios of 65%, 75%, 85%, and 95%. The Strain-Softening model was used to calibrate the backfill material parameters. The results showed that as the backfill ratio increased, the support provided by the backfill material improved, leading to enhanced bearing capacity of the overlying strata, reduced mine pressure intensity, significantly decreased deformation of the roadway, and substantially improved stability of the surrounding rock. Third, under a backfill ratio of 95%, the evolution of the abutment stress during face advancement was investigated. It was found that as the working face advanced, the backfill material and the overlying strata gradually formed a stable composite structure, with the abutment stress in the mining area stabilizing over time. Finally, to address the issue of insufficient initial strength and limited support capacity of the paste backfill material, a comprehensive control system for surrounding rock stability was proposed. This system integrates a basic bolt-mesh-cable support structure with localized reinforcement using portal hydraulic supports. Field industrial practices demonstrated that after applying this comprehensive control technology, the convergence of roof and floor was approximately 190 mm and the convergence of two ribs was about 140 mm, effectively ensuring the stability of surrounding rock in GER with paste backfill working face. Full article

Understanding the enhancing mechanisms of graphene oxide (GO) on the pore structure characteristics in the interfacial transition zone (ITZ) plays a crucial role in cemented waste rock backfill (CWRB) nanoreinforcement. In the present work, an innovative method based on metal intrusion techniques, backscattered electron (BSE) images, and deep learning is proposed to analyze the micro/nanoscale characteristics of microstructures in the GO-enhanced ITZ. The results showed that the addition of GO reduced the interpore connectivity and the porosity at different pore throats by 53.5–53.8%. GO promotes hydration reaction in the ITZ region; reduces pore circularity, solidity, and aspect ratio; enhances the mechanical strength of CWRB; and reduces transport performance to form a dense microstructure in the ITZ. Deep learning-based analyses were then proposed to classify and recognize BSE image features, with a high average recognition accuracy of 95.8%. After that, the deep Taylor decomposition (DTD) algorithm successfully located the enhanced features of graphene oxide modification in the ITZ. The calculation and verification of the typical pore optimization area of the location show that the optimization efficiency reaches 9.6–9.8%. This study not only demonstrated the deepening of the enhancement effect of GO on the pore structure in cement composites and provided new insights for the structural modification application of GO but also revealed the application prospect of GO in the strengthening of CWRB composites and solid waste recycling. Full article

This study aimed to investigate the effects of the cement-tailings ratio (CTR) on the fatigue properties, acoustic emission (AE) activities, energy dissipation, and fracture patterns of rock-backfill composite structure (RBCS) samples. The investigation employed multi-level cyclic loading tests combined with acoustic emission monitoring and post-test CT scanning. The results indicated that the fatigue strength and fatigue lifetime of the RBCS samples initially increased and then decreased as the CTR was reduced from 1:4 to 1:12. The energy dissipation characteristics reflected the optimal energy absorption effect of the backfill at a CTR of 1:8. The AE ring counts/energy apparent skip phenomenon corresponded to the stress-strain curve from a dense to sparse pattern. The samples with CTRs of 1:4 and 1:8 showed a more significant increase in the peak frequency band at failure and released more energy. The fracture of the RBCS specimen was dominated by tensile cracking signals accompanied by some shear cracking signals. However, the proportion of shear signals was higher for samples with CTRs of 1:4 and 1:8. Similarly, the b value was smaller at failure. The 3D visualization images revealed that the fracture pattern of the RBCS was a mixed tensile-shear fracture, including shear fracture within the backfill, tensile cracking in the interface, and tensile-shear fracture within the rock. The volume and complexity of cracks increased and then decreased with decreasing CTR, i.e., from 1:4 to 1:12. The evolution of cracks probably involves internal backfill fracturing first, and then the fracture extends into the surrounding rock. A recommendation for the design of CTB was presented in this study to ensure the safety and stability of mine excavations. Full article

Unveiling the mechanical properties and damage mechanism of the complex composite structure, comprising backfill and surrounding rock, is crucial for ensuring the safe development of the downward-approach backfill mining method. This work conducts biaxial compression tests on backfill–rock under various loading conditions. The damage process is analyzed using DIC and acoustic emission (AE) techniques, while the distribution of AE events at different loading stages is explored. Additionally, the dominant failure forms of specimens are studied through multifractal analysis. The damage evolution law of backfill–rock combinations is elucidated. The results indicate that DIC and AE provide consistent descriptions of specimen damage, and the damage evolution of backfill–rock composite specimens varies notably under different loading conditions, offering valuable insights for engineering site safety protection. Full article

The pore-throat characteristics significantly affect the consolidated properties, such as the mechanical and permeability-related performance of the cementitious composites. By virtue of the nucleation and pore-infilling effects, graphene oxide (GO) has been proven as a great additive in reinforcing cement-based materials. However, the quantitative characterization reports of GO on the pore-throat connection are limited. This study applied advanced metal intrusion and backscattered electron (BSE) microscopy scanning technology to investigate the pore-throat connection characteristics of the cement waste rock backfill (CWRB) specimens before and after GO modification. The results show that the microscopic pore structure of CWRB is significantly improved by the GO nanosheets, manifested by a decrease in the total porosity up to 31.2%. With the assistance of the GO, the transfer among internal pores is from large equivalent pore size distribution to small equivalent pore size distribution. The fitting relationship between strength enhancement and pore reinforcement efficiency under different pore-throat characteristics reveals that the 1.70 μm pore-throat owns the highest correlation in the CWRB specimens, implying apply GO nanosheets to optimizing the pore-throat under this interval is most efficient. Overall, this research broadens our understanding of the pore-throat connection characteristics of CWRB and stimulates the potential application of GO in enhancing the mechanical properties and microstructure of CWRB. Full article

In this paper, the straight-wall-arch structure in the rock medium is taken as the research object, and the high-pressure plane charge loading test technology is adopted to study the anti-explosion performance of different types of structures under the explosion loading. Three types of structures, which are individually built with the high-performance reinforced concrete, the C30 reinforced concrete, and the C30 reinforced concrete with a foam concrete backfill layer as well, are tested, and the dynamic responses and damage characteristics of these structures are investigated. The test results show that under the condition of the same plane charge explosion loading, in the vault of the high-performance reinforced concrete test section appears a through-tensile crack with a largest transverse relative displacement between the two straight walls, and the composite structure test section only shows an intermittent crack at the arch foot, which represents a slight damage mode. Meanwhile the arch spring of the C30 reinforced concrete test section suffers a through-compression shear failure with a largest vertical relative displacement between the vault and the floor, which represents a moderate damage mode. Therefore, adopting the high-performance reinforced concrete, and the C30 reinforced concrete with the foam concrete backfill layer, can effectively decrease the damage degree of the rock structures. Compared with the C30 reinforced concrete, the high-performance reinforced concrete can improve the resistance of the structure by improving the structural strength and strengthening its capacity to absorb waves and energy dissipation, and the foam concrete backfill layer can significantly reduce the lateral and vertical relative displacement of the structural free surface and the peak stress of the structural inner layer. The composite structure test section of the C30 reinforced concrete with foam concrete backfill layer appears to be an excellent anti-explosion performance property. Full article

The backfill in the stope usually forms a composite structure with the surrounding rock in order to bear pressure together to support the goaf and ensure the safe mining of subsequent ores. Based on laboratory tests and theoretical analysis, the energy and damage evolution of the rock–backfill composite materials (RBCM) are studied deeply. The results show that: (1) The σ_p (peak stress), ε_p (peak strain), and E (elasticity modulus) decreased with the increase of the internal backfill diameter. When the diameter of the backfill increases from 10 mm to 40 mm, σ_p decreases from 50.15 MPa to 18.14 MPa, ε_p decreases from 1.246% to 1.017%, and E decreases from 7.51 GPa to 2.33 GPa. The U^T shows an S-shaped distribution, the U^E shows an inverted U-shaped distribution, and the U^D first increases slowly and then increases rapidly. The U^T_p, U^E_p, U^D_p, U^E_p/U^D_p, and U^E_p/U^T_p decrease by 67.38%, 97.20%, 58.56%, 32.64% and 13.64% respectively, and the U^D_p/U^T_P increases by 20.93% with the increases of the backfill diameter. (2) A damage constitutive model of the RBCM is established based on the energy consumption characteristics. The damage evolution curve shows an S-shaped distribution, and the damage rate evolution curve shows an inverted U-shaped distribution. (3) The AE correlation fractal dimension decreases with the increase of the strain gradient and damage value, and the AE correlation fractal dimension presents linear and exponential functions with them, respectively. With the increase of stress, microcracks first appear and gather in the internal backfill of the RBCM, and then microcracks appear and gather in the peripheral rock, which together lead to the macro penetration failure of the RBCM. Full article

In underground metal mines that use sublevel or stage open-stope and backfilling mining methods (SSOBMMs), there is a special structure around which both sides of the rock pillar are wrapped by backfill. As a permanent part of an underground mine, how much can backfill improve the rock pillar’s compressive strength? What is the difference in the mechanical properties between the special structure and the signal rock? To explore these questions, a composite structure made of a cement-tailing backfill (CTB) and rock core (RC) was designed. Uniaxial and triaxial compressive strength tests and scanning electron microscope (SEM) were used to research the mechanical properties, failure process, failure characteristics, and microstructure characteristics of the cement-tailing backfill and rock core (CTB-RC) specimens. It was found that the full stress–strain curve of the CTB-RC specimen under triaxial compressive strength (TCS) test had two times the stress increases reaching a lower peak deviator stress two times after the RC was destroyed. The CTB can reduce the destruction and slow down the deformation speed of the inner rock cor (IRC). It can also prevent rigid slip of the IRC after it is damaged and maintain the stability and integrity of the overall structure. The findings of this study can provide some basic knowledge on the mechanical properties of the CTB-RB and provide theoretical guidance for the optimization direction of the width of the rock pillar and the room in mines using SSOBMMs. Full article

The artificial-caved rock composited backfilling approach can effectively restrain the dynamic phenomena in the coal seam and the associated roof and floor during mining operations, and can also improve the stability of the system of support and surrounding rock. In this study, based on the analysis of influencing factors affecting the surrounding rock movement and deformation of the composited backfilling longwall face in a steeply dipping coal seam, the roof mechanical model is developed, and the deflection differential equation is derived, to obtain the roof damage structure and the location of the roof fracture for the area without backfilling. The migration law of the roof under different inclination angles, mining depths, working face lengths, and backfilling ratios are analyzed. Finally, mine pressure is detected in the tested working face. Results show that the roof deflection, bending moment, and rotation drop with the increase of the inclination angle and backfilling ratio, whereas these parameters increase with greater mining depth and working face length. The roof failure location moves toward the upper area of the working face as the inclination angle and working face length increases, while it moves toward the center of the non-backfilling area with greater mining depth and backfilling ratio. Results from the proposed mechanical model agree well with the field test results, demonstrating the validity of the model, which can provide theoretical basis for a safe and efficient mining operation in steeply dipping coal seams. Full article