Fracture evolution of rock–backfill composites (RBCs) under complex loading–unloading and dynamic disturbances is critical for stope stability in deep backfill mining. Using PFC3D, this study constructs numerical models of RBCs to investigate this process, considering burial depths (500, 1000, 1500, 2000 m), interface angles (IA: 60°, 90°), and cement–tailings ratios (CTR—1:4, 1:8), while replicating true triaxial paths and blasting impacts. Systematic analysis of mesoscopic crack quantity, spatiotemporal distribution, and multiscale fracturing reveals that shear cracks dominate damage, with crack counts evolving in stages as strain increases. With greater depth, the number of propagation stages and growth rate inflection points shift systematically. During mining–filling disturbance, crack quantity negatively correlates with depth but turns positive during late static loading beyond 70% peak stress. Spatial crack distribution is synergistically controlled by IA, CTR, and depth. For IA 60°, shear crack angles spread broadly yet concentrate at 50–70°; for IA 90°, they are near-axial, concentrated at 80–90°. The synergistic process progresses through microscopic initiation, mesoscopic accumulation, and macroscopic instability. In terms of failure modes, IA 60° exhibits shear failure along the cemented interface plus tensile fracturing in rock, while IA 90° shows combined diagonal shear and axial tension. Higher CTR yields more extensive fracture networks in backfill, indicating superior synergistic bearing capacity.
Hongjian Lu, Zhaoyang Ren, Fan Jiang· Minerals· 0 citations
This book is intended as a reference book for advanced graduate students and research engineers in rock mechanics related to mining engineering. The cemented tailings backfill (CTB) technique is widely used in deep underground mining, since this technique is effective to support surrounding rock, control rockburst, reduce ground subsistence, and reduce surface disposal of tailings. Plenty of investigations have been attempted to experimentally or numerically evaluate the strength of CTB with different components (e.g., mixture of cement, tailings, fly ash, blast furnace slag, etc.) to ensure the geological stability when extracting adjacent stopes. After extracting ore from stopes, CTB is filled in the gob, stress redistribution occurs in the backfill stope and surrounding rocks. Due to the elasticity mismatch of these two kinds of material, differential deformation occurs and they both resist the overburden pressure and deformation. As a result, the interactions between the surrounding rock and tailing backfill material have significant role in maintaining the long-term stability of mine stopes. Apart from the investigations on the static mechanical behaviors of rock-backfill composited backfill (RBCS) material, the RBCS in the stope are also exposed to disturbed stress (e.g., blast vibration, excavation, earthquake, etc.), and the disturbed stress is usually equivalent to cyclic or fatigue loads. As a result, investigations on rock-backfill interactions subjected to the disturbed stress are critical and significant to maintain the long- term stability of mine stopes.
In this study, we explore the static and dynamic mechanical responses of layered cemented backfill subjected to blasting loads. Variable-rate uniaxial compression tests and Split Hopkinson Pressure Bar (SHPB) numerical simulations were performed on specimens with three different interlayer cement-to-tailings ratios. All samples were cured for 28 days before testing. The test results reveal that uniaxial compressive strength rises and then falls with increasing loading rates, and mixed tensile-shear failure dominates quasi-static loading conditions. The interlayer cement-to-tailings ratio dominates the bearing capacity of backfill. At the test loading rate of 0.02 mm/s, lowering the interlayer ratio from 1:4 to 1:8 sharply reduces peak strength from 5.595 MPa to 1.285 MPa, with a total drop of 77.0%. SHPB simulation results show obvious strain-rate hardening under dynamic impact. For samples with an interlayer ratio of 1:4, dynamic compressive strength increases from 5.38 MPa to 6.16 MPa as impact velocity rises from 4 m/s to 13 m/s, a 14.5% improvement caused by rapid compaction of internal micropores. Combining damage mechanics and energy conservation principles, we establish a dynamic damage constitutive model that couples inherent layered interfacial damage with blasting-induced dynamic disturbance. Model predictions match experimental measurements well. The peak strength error is only 1.3% at a loading rate of 0.005 mm/s, and peak deviations for all test cases are controlled within 5.0%. This work quantitatively clarifies the static and dynamic mechanical evolution of layered cemented backfill, and provides solid theoretical support for mixture proportion design and blasting stability assessment in high-stage sequential backfilling mining.
The stability of slice drifts is critical to the safety and sustainability of mining operations. In underhand cemented backfill mining, slice drifts may be subjected to a special condition in which both the roof and sidewalls are composed of cemented backfill. Therefore, evaluating their long-term stability is of significant engineering importance. To analyze the time-dependent deformation of this special structure, the roof and sidewalls were idealized as a fixed-end beam and a fixed-end wall, respectively. Burgers creep compliance was then incorporated to derive time-dependent expressions for roof subsidence and sidewall convergence. The effects of slice-drift width, in situ stress conditions, and creep influence range on deformation were then analyzed. Subsequently, a three-dimensional FLAC3D 6.0 model incorporating the actual excavation, backfilling, and creep processes was established. The Mohr–Coulomb and Burgers constitutive models were used to investigate the evolution of stress and deformation in slice drifts with different widths. The results show that increasing the slice-drift width significantly increases the roof tensile stress and sidewall convergence rate. Under the extreme condition in which four adjacent drifts on both sides are excavated simultaneously, roof tensile stress concentration and drift deformation are further intensified. Considering both the roof tensile stress and the allowable convergence rate during the stable creep stage of the sidewalls, a slice-drift width of 5.0 m is recommended. Finally, field convergence monitoring was conducted at eight monitoring points in two slice drifts with widths of 4.8–5.08 m. The monitoring results show that the average convergence rates within this width range were lower than 0.25 mm/d, satisfying the stability requirement. These observations support the reasonableness of the numerical results and the recommended slice-drift width. The findings provide a reference for long-term stability assessment and width design of backfill-formed slice drifts in underhand backfill mining.
Jilong Pan, Qinli Zhang, Yan Feng et al.· Applied Sciences· 0 citations
In civil engineering projects, the practice of partial excavation or backfilling of slopes often results in landslide occurrences because of the redistribution of internal stress within the slope mass. This paper presents the findings from scaled-model tests conducted to investigate the reinforcement of high-fill embankment slopes using anti-slide piles. During the filling process, data were meticulously monitored using strain gauges affixed to the pile bodies and embedded earth pressure cells. The analysis focused on the mechanical behavior, including load–displacement relationships at the pile tops, bending moments, and earth pressures. This study was designed to investigate how anti-slide piles contribute to slope stabilization and to evaluate their load-bearing behavior throughout the backfilling process. Additionally, particle image velocimetry technology was used to capture the variation patterns of the soil surface displacement field, thereby revealing soil displacement deformation and the overall failure mechanism. By integrating mechanical responses with the analysis of the soil displacement field, a more profound understanding of the pile–soil interaction mechanism was attained. This experimental method provided a comprehensive depiction of the entire process, from the initial slope movement to its eventual deformation and failure. The research indicates that a reduction in pile spacing leads to a decrease in the maximum bending moment of the pile body, thereby enhancing slope reinforcement. For the same pile spacing, the pile located on the first-level slope platform shows the smallest horizontal displacement at its top after deformation. The soil on either side of the anti-slide pile disperses outward from the pile body, with the maximum displacement occurring directly beneath the pile tip.
Bingxiang Yuan, Weiyuan Xu, Kaipeng Yang et al.· Journal of Testing and Evalu...· 0 citations
Cemented paste backfill (CPB) is widely used in mining, but its high brittleness, low toughness, and limited ductility can cause it to crack and spall, or even damage the overall structure, thereby limiting its application in deep underground mine excavations. To this end, this study investigates the damage and failure mechanisms of cemented gangue–rubber paste backfill (CGRPB) and analyses its energy evolution characteristics. The aims are to: (i) assess the CGRPB mechanical properties, i.e., toughness, ductility, and brittleness due to incorporating rubber; (ii) analyze the fracture propagation process of CGRPB from an energy evolution perspective. Therefore, monotonic and cyclic compression tests were conducted on CGRPB samples containing 0%, 5%, and 10% recycled rubber powder. This study focuses on analyzing compressive strength, failure modes, stress–strain responses, energy evolution and the damage evolution process. Key findings include: (1)the effect of rubber incorporation on strength is dosage- and curing-age-dependent; a moderate rubber content (5%) improves early-age strength, whereas excessive rubber addition reduces strength due to increased porosity and weakened load-bearing capacity; (2) samples with rubber significantly reduce the length, number, and width of cracks, achieving better structural integrity; (3) introducing rubber improves the pre-peak deformation capacity of the samples; (4) the strain growth magnitude is positively correlated with the rubber content, enhancing their toughness and ductility; (5) adding rubber effectively reduces the damage propagation rate within the sample; (6) under loading, rubber elastic deformation in samples dissipates energy, which describes the approximately linear energy storage and dissipation trend; (7) among the investigated rubber contents, 5% rubber incorporation achieved a favorable balance between mechanical strength, toughness, and ductility.
Chengjin Gu, M. Silva, Baogui Yang et al.· Mining· 0 citations
