Publications

In constructional backfill mining, due to differences in mining and backfill speed, the backfill body is subjected to loads with different loading rates. To investigate the effect of the loading rate on the failure characteristics of the backfill body, uniaxial compression tests were conducted on cemented gangue backfill body (CGB) with loading rates ranging from 0.15 mm/min to 2.4 mm/min, assisted by digital image correlation (DIC) and acoustic emission (AE) monitoring. The cracks in the specimens were classified based on RA-AF data using expectation maximization (EM) algorithms and a Gaussian mixture model (GMM). Energy analysis was also performed to examine the failure characteristics and patterns of the specimens. The results reveal that as the loading rate increases, the compressive strength of the specimen first increases and then decreases, reaching a maximum of 13.72 MPa at 0.6 mm/min. The occurrence of major internal failure within the specimen shifts forward from the elastic stage to the compaction stage, and the concentration and intensity of the failure location increase. The density of cracks on the surface of the specimens shows a trend of first increasing and then decreasing. The internal cracks in the test specimens are mainly shear cracks, but as the loading rate increases, the proportion of internal shear cracks first decreases and then increases. At 0.6 mm/min, the proportion reaches its lowest value of 73.90%. The proportion of shear cracks is one of the important factors affecting the strength of the CGB under different loading rates. The dissipated energy during specimen failure shows a trend of first increasing and then decreasing. The energy value used for specimen failure at 0.6 mm/min is the highest, reaching 24.589 kJ·m -3 . The research results are expected to provide a basis for determining the stability of CGB under different mining speeds, thereby ensuring the efficient and safe operation of backfill mining.

Stability of backfill roof in underhand cut-and-fill mining is crucial to production safety, as personnel and equipment often work directly beneath it. The interfaces (or cold joints) between adjacent drifts, which result from the primary-and-secondary mining sequence, typically exhibit lower strength compared to the backfill matrix. These weaker interfaces can compromise the integrity and stability of the backfill roof. Additionally, they lead to two distinct drift layouts: an aligned drift layout and a staggered drift layout. Clearly, the stability of backfill roof is closely associated with both the interfaces and the drift layout. However, in previous studies, backfill roof was generally treated as an intact structure, with less attention paid to the influence of drift layout. In this paper, the interfaces between filled drifts were explicitly considered to investigate the stability of the backfill roof. Failure modes and strength requirements of the backfill roof for both aligned and staggered drift layouts were comprehensively analysed using numerical modelling with FLAC3D. Four distinct failure modes of the backfill roof were identified based on the evolution of plastic zones and displacement contours: block sliding, top caving, bottom caving, and sloughing. For the aligned drift layout, an increase in interface strength was found to trigger a transformation in failure modes, accompanied by a reduction in strength requirements. When the interface strength was further increased, the backfill roof in the aligned drift layout behaved as if no interfaces existed between the drifts. In contrast, for the staggered drift layout, failure modes and strength requirements of backfill roof were barely affected by the interface strength, regardless of whether the interface had no strength or was as strong as the backfill matrix. These findings are expected to provide valuable insights for mining engineers to optimize drift layout and implement cost-effective backfill designs in underhand cut-and-fill mining.

To increase annual ore production and reduce mining costs, the Black Mountain Mine in South Africa introduced the long-hole mining method. The existing hydraulic fill backfill system, designed for cut- and-fill stopes, could not cope with the new life of mine schedule. A backfill system upgrade project was launched to increase backfill production to enable timely filling of the long hole stopes. Analysis of the existing system identified issues related to safety, performance, reliability, and excessive downtime in the underground distribution system, the latter which accounted for 47% of total system downtime. Short-term interventions addressed immediate safety and production concerns, followed by a comprehensive engineering upgrade to improve system performance. The backfill system optimisation process focused on technical improvements to the underground distribution system using hydraulic modelling, an identification of the system ′s most vulnerable components and analysing the dominant wear mechanisms at those locations. In parallel, backfill system utilisation was addressed and the mine prepared for long-hole filling by backfill integrated operations management which included personnel training to promote backfill system understanding and promote cross-departmental knowledge sharing. A structured approach to preventative maintenance was sought and an all-encompassing backfill management plan was created. The paper will present a comprehensive discussion of the steps and processes followed in successfully reducing system downtime and doubling the annual backfill production. Key learnings that can be applied to other active backfilling operations include the value of a structured approach to underground distribution system diagnostics, the prioritisation of upgrades in accordance with the mine schedule, the need for a detailed technical understanding of hydraulic challenges, and the critical role of securing workforce buy-in to achieve and sustain backfill objectives.

Backfilling is a critical step in underground mining, providing rockmass confinement and enabling safe extraction of ore. Current practice is dominated by monolithic pour designs where the stope is treated as a uniform body with consistent strength requirement. While this approach offers simplicity, it neglects the complex interplay of flow, placement, and exposure conditions that drive performance and binder consumption. This paper introduces a methodology for transitioning from monolithic to segmented backfill design through integrated flow and strength modelling. By simulating the flow of paste into a stope, we establish the spatial and temporal sequence of fill, enabling segmentation (“banding”) into zones with distinct strength targets. These targets are determined dynamically, reflecting both material placement and the exposure conditions that govern stability. To support this framework, we evaluate predictive models for backfill strength beyond the traditional water-to-cement ratio approach, which dominates current practice. Using machine learning methods including neural networks, random forest, and XGBoost, we demonstrate the capacity to capture higher-dimensional interactions between mix design, curing time, and various process SCADA streams. These more accurate strength prediction models facilitate just-in-time strength design, supporting mine scheduling with dynamic curing time designs and reliable exposure date forecasting. The methodology is applied to an active mining case study, where segmented design and advanced prediction models together reduce binder usage by 32% without compromising safety. These results highlight both the practical benefits and the conceptual shift required for backfill design: moving from uniform monolithic pours toward granular, data-driven design strategies that optimise material use while ensuring structural reliability.

To address the persistent challenge of accurately predicting the unconfined compressive strength (UCS) of cemented paste backfill (CPB) in underground mining applications, this study develops a hybrid intelligent model integrating quantum-behaved particle swarm optimization (QPSO) with a fully connected neural network (FCNN). A comprehensive database comprising 383 laboratory test samples was compiled from multiple published experimental studies, encompassing eight input variables—non-uniformity coefficient of tailings, chemical composition (CaO and MgO), cement grade, tailings-to-cement ratio (T/C), slurry mass concentration, curing temperature, and curing time—and one output variable, UCS. The QPSO algorithm was employed to perform a global optimization of critical hyperparameters (hidden nodes, learning rate, regularization coefficient, dropout rate, and batch size) within a high-dimensional continuous search space. Subsequently, the Adam optimizer was applied for deterministic fine-tuning of network weights, yielding concurrent enhancements in convergence efficiency and predictive accuracy. Furthermore, Shapley additive explanations (SHAP), ±10% perturbation analysis, and partial dependence plots (PDPs) were utilized to quantitatively evaluate the global importance, local marginal effects, and interactive sensitivities of input parameters. The proposed model exhibited outstanding predictive performance, achieving an R ² of 0.969, RMSE of 0.198 MPa, MAE of 0.139 MPa, and a composite performance score of 0.930, surpassing both conventional FCNN and QPSO-BP hybrid models. Sensitivity analysis revealed that the tailings-to-cement ratio and curing time were the most influential factors, while pronounced coupling effects occurred between tailings gradation and slurry concentration as well as between curing conditions and T/C ratio. These results provide robust quantitative insights for optimizing the mix design and curing regimes of CPB, thereby enhancing its mechanical reliability and supporting sustainable underground mining operations.

The global mining industry faces criticism due to substantial production of tailings and carbon emissions, demanding urgent sustainable strategies. Mineral carbonized mine backfilling integrated with CO 2 offers a more suitable strategy for addressing these issues. However, this technology is not yet mature for backfills due to knowledge gaps persistent in CO 2 injection optimization, mechanical characteristics, and pore structure refinement during preparation. This study investigates the influence of CO 2 injection rates through slurry on mechanical properties and pore structure evolution at ambient conditions using a self-made novel multifunctional closed reactor. A series of experiments was conducted to optimize the process. The highest uniaxial compressive strength (UCS) of 2.589 MPa was achieved at 10 min CO 2 injection, a 93.2% increase over non-carbonated sample, simultaneously sequestering 6.5% CO 2 by weight. The porosity reduced from non-carbonated samples (10.5%) to optimal samples (8.1%). The secondary pores decreased up to 30 % while micropores increased to 60%. Thermogravimetric analysis (TGA) showed a weight loss of 6.48% attributed to the decomposition of CaCO3. Microstructure analysis using scanning electron microscopy (SEM) and low-field nuclear magnetic resonance (LF-NMR) confirmed that calcite (CaCO 3) was formed during mineralization reaction, which densified the matrix, reduced porosity by 29.6%, and caused pore refinement through transformation of secondary pores to micropores. A strong linear correlation was established between porosity and UCS (R 2 = 0.795). However, prolonged CO2 injection deteriorates strength and pore refinement due to formation of dense CaCO 3 passivating boundary that blocks pore network, hindering further diffusion of CO 2 and reducing carbon sequestration. Hence, controlled and optimized CO 2 injection rates are required for pore refinement and enhancement of the overall mechanical integrity of the backfill. This study provides a triple-advantage pathway for improved tailing management and permanent carbon sequestration within underground mine backfill, contributing to safer and more sustainable mining practices.

Macroscopic and microscopic properties of cemented tailings backfill (CTB) were studied through uniaxial compressive testing, acoustic emission (AE) monitoring and microscopic feature analysis. The research shows that the uniaxial compressive strength (UCS) and elastic modulus have an exponential function y=ae bx +c type positive correlation with the increase of curing time and a polynomial function y=ax 2 +bx+c type wiuj6th the rise of curing temperature, the mechanical parameters reach the maximum when the curing temperature is 40 °C. Increasing the curing time and curing temperature can promote the transition from shear crack to tensile crack. Increasing the curing time and raising the curing temperature both promote the transition of shear crack to tensile crack in the CTB. Overall, the crack mode is a combination of tensile and shear crack. At room temperature, shear crack dominates in the initial stage, but the proportion of shear crack decreases as the pressure increases. At a curing temperature of 60 °C, the crack mode transitions to a tensile-shear mixed crack, with tension becoming the dominant crack mode. Microscopic analysis suggests an excellent linear correlation between the pore fractal dimension, UCS, and elastic modulus. When the pore fractal dimension decreases, the mechanical parameters also decrease. The pore fractal dimension can effectively characterize the macroscopic mechanical properties. Finally, the curing temperature is divided into two stages, with 40℃ as the dividing line for analysis. In the first stage, the increase in curing temperature effectively improved the mechanical parameters; in the second stage, the excessively high hydration reaction rate weakened the mechanical parameters.

In the global map, coal mining extraction is predominantly governed by the opencast (OC) method of mining. India and several major coal-producing regions around the world rely heavily on opencast mining to extract coal. Currently, over 95% of India′s coal is produced through this method. As finite resources and ecological concerns become more apparent, the mining industry must adopt and practice sustainable mining techniques to protect the environment and manage resources responsibly. The process of opencast coal mining offers a high level of productivity and operational fluidity, but on the other hand, it is also associated with huge mine voids, significant overburden quantities, challenging land acquisitions, and extensive land disturbances. Because of this, mine closure planning poses a techno- economic and environmental challenge. It is important to note that, although backfilling is widely implemented in OC mines as a mitigation measure, backfill planning is often driven by production requirements rather than by the feasibility of long-term closure. This work presents a strategic integrated backfill planning decision support framework (IBP-DSF) for the sustainable closure-oriented planning of opencast coal mines. A set of normalized indices is compiled by aggregating the geometric characteristics of the mine, the availability of materials, pit depth, geotechnical stability, hydro-environmental sensitivity, and economic feasibility into an integrated backfill planning score (IBPS). Based on threshold values, the IBP-DSF classified mine closures into four types of closure strategies. The IBP-DSF tool is applied to brownfield and greenfield Indian OC coal mines and further examined using hypothetical case scenarios. Physical-economic and ecological considerations limit the feasibility of full backfilling, whereas partial backfilling and alternative void management strategies can be more realistic and sustainable closures. This framework provides a transparent, generalized decision support tool that supports realistic closure commitments, optimizes land use, and reduces risks for long-term environmental, financial, and social sustainability.

The sustainable reuse of industrial by-products in mine backfilling has attracted growing attention in underground mining practice. Cement kiln dust (CKD), a major waste from cement production, offers potential as a supplementary binder in cemented backfill, yet its performance under blasting disturbance is not well investigated. This study examines the mechanical response and stability of CKD-based backfill subjected to underground blasting through numerical simulation. A dynamic modelling framework was developed to capture the rock-backfill interaction. Blast loading was represented by pressure-time functions of varying intensity and pulse duration. Parametric studies were conducted, considering the effects of blast intensity, pulse duration, distance from the source, and uniaxial compression of backfill. Mechanical indicators, including displacement, stress redistribution, and energy absorption, were employed to assess backfill mechanical performance and stope stability. The results indicate that lower compression strength significantly improves dynamic resistance, whereas intense, short-duration blasts accelerate damage accumulation. Blast proximity strongly governs energy transfer and failure mode. These findings will provide quantitative insights into the dynamic performance of CKD-based backfills and highlight practical guidelines for designing resilient and sustainable underground backfilling systems.

Paste backfill relying on deep-cone thickening represents a complex systems engineering challenge. Achieving stable thickening, consistent paste quality, and efficient process control remains a critical challenge for the metal mining industry. Recent advances in computational intelligence offer new opportunities to improve system efficiency and operational stability. Using data from a Mongolian zinc mine with high-specific-gravity tailings (SG=3.459), this study proposes a multivariate LSTM- based predictive model for underflow concentration. Leveraging historical data on four key variables, the model employs a sliding-window mechanism to perform recursive three-hour-ahead forecasts of underflow concentration. The model achieved high training accuracy (R ² = 0.92) and robust test performance (MAE=0.42%, RMSE=0.48%), confirming its suitability for engineering applications. Simulations under three discharge rates (40, 50, 60 m³/h) indicated that solely maximizing discharge rate is suboptimal. Accordingly, a “predict–evaluate–regulate” feedforward control framework is proposed, shifting operations from reactive feedback to proactive regulation. Industrial trials maintained a slurry bed height of approximately 5.5 m. Proactive discharge-rate regulation sustained underflow concentration at 70%–82% for seven hours, enabling consistent preparation of high-quality paste (74%–76% solids content). In the stope, the backfill provided sufficient bearing capacity for personnel access within 10 hours at low cement-to-tailings ratios, achieving 1.5 MPa after one day and exceeding 3 MPa after three days at higher ratios. The proposed predictive model offers a quantitative tool and a methodological pathway for optimizing discharge strategies and facilitating feedforward control in deep-cone thickening.

Assessing core samples retrieved from boreholes in mining areas is critical for mine fill design, as it enables the early identification of potential mechanical and environmental risks. This study experimentally investigates the strength and microstructural behavior of cementitious backfill (CPB), broadly used for sustainable re-filling of underground voids. In this context, CPB mixtures were prepared using core samples obtained from a copper mine and binder (Ordinary Portland, CEM I) at different cement ratios (5%, 7%, 9%, and 11%, by weight) and three solid contents (66%, 74% and 82%, by weight). Strength development was evaluated with uniaxial compressive strength (UCS) tests executed at 3-28-day curing days. Microstructural properties were investigated with SEM: scanning electron microscopy, FTIR: Fourier-transform infrared spectroscopy, and TGA: thermogravimetric analysis. The findings revealed that cement dosage are decisive in C–S–H formation, porosity development, and CPB strength gain. Furthermore, this study showed that rising age caused further development of CPB microstructure with less pores, more hydration products and greater mechanical stability. Finally, the findings contribute to the design of durable and economical fill incorporating core samples suitable for prospective complex subsurface conditions.

In open-stope subsequent filling mining, the impact load from second-step orebody blasting threatens the stability of the first-step backfill, and rock thickness (RT) is a key factor regulating the mechanical behavior of rock-backfill composites (RBC). However, existing damage constitutive models fail to accurately capture the three-stage damage evolution (linear elastic deformation, plastic yield, post- peak failure) of RBC under impact loading, especially the post-peak softening characteristics, which limits the scientific design of pillar thickness and the safety of mining operations. To address this engineering and academic gap, this study adopted the split Hopkinson pressure bar (SHPB) system to conduct impact tests on RBC specimens with four RT levels, obtaining stress-strain curves and damage evolution data under impact loading. A novel three-stage damage constitutive model (TS model) was established by integrating Lemaitre's strain equivalence principle and the Mazars method, with innovative consideration of residual strength in boundary conditions to improve prediction accuracy. Additionally, the TS model was systematically compared with the Weibull distribution- based model (WD model) and energy-based model (EM model) via error analysis and regression analysis. This study clarifies the regulatory effect of RT on the anti-impact performance of RBC and provides a reliable constitutive model for predicting its damage behavior, offering theoretical basis and engineering reference for the stability control of filling mining systems.

Aiming at the prominent problems of high cost of cementitious materials and low CO 2 sequestration efficiency in mine filling, this study systematically explored the influence mechanism of the mineral activator carbide slag (CS) and its composite activation with Na 2SiO3 (sodium silicate, S S) on the properties of low-activity electric arc furnace slag (EAFS)and granulated blast furnace slag (GBFS)- based cementitious materials. By preparing carbon-sequestering backfill materials with CS and CS-S S as activators, mineralization tests were conducted under controlled CO 2 curing parameters (pressure: 0.2–0.4 MPa, concentration: 20%–60%, curing duration: 1–4 h). Comprehensive characterization via X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), thermogravimetry- differential scanning calorimetry (TG-DSC), and scanning electron microscopy (SEM) was performed to elucidate the evolution of hydration products and microstructures. It was revealed from the experimental results that, for CS single-activation system, the 3-day and 7-day uniaxial compressive strengths (UCS) of the cementitious materials decreased with an increasing EAFS replacement ratio. The UCS peaked at 6.81 MPa (3-day) and 10.96 MPa (7-day) when EAFS replacement was 20% (with 20% or 30% CS, respectively). However, excessive CS reduced strength due to insufficient GBFS participation. The CS-SS synergistic activation system exhibited superior early-age strength (17.66 MPa at 3-day or 22.01 MPa at 7-day), confirming the dominant role of S S in early hydration. Mineralization significantly enhanced the performance of CS single-activation system: the 3-day strength increased by 1.90–2.77 times (reaching 11.6 MPa) compared to the control group (4.2 MPa), but it weakened CS-SS synergistic activation system. It was identified via orthogonal analysis that CO 2 concentration (40%) was the primary factor influencing the 3-day strength of CS single-activation system, followed by pressure (0.4 MPa) and curing duration (1 h). This validates that mineralization can be achieved under non-pure CO 2 and non-high-pressure conditions. Microstructural analyses showed that CS single-activation system promoted the formation of C-(A)-S-H gel and CaCO 3, whereas composite systems underwent decalcification of C-(A)-S-H gels during mineralization. This study uncovers the synergistic advantages of CS under CO 2 mineralization conditions and the incompatibility between CS-SS synergistic activation system and CO 2 mineralization curing, providing theoretical foundations and technical pathways for developing low-cost mine backfill materials with high CO 2 sequestration capacity.

In-situ mining environmental factors, including temperature, pressure, and pore water pressure, significantly alter the curing process of cemented tailings backfill. This leads to pronounced discrepancies in mechanical properties between laboratory specimens prepared with identical mix ratio and core samples extracted from mining stopes. Accurate prediction of the mechanical properties of cemented paste backfill (CPB) under in-situ conditions is a critical prerequisite for achieving economically optimal design of backfill mix proportions in mining operations. While substantial research has been conducted globally on the influence of individual environmental factors on tailings backfill properties, quantitative studies addressing the coupled effects of multiple environmental factors remain relatively scarce. This paper systematically reviews the current state of research on the mechanical properties of tailings cemented backfill under in-situ conditions in mining areas. Focusing on three core in-situ environmental factors—curing pressure, curing temperature, and pore water pressure—it analyzes their influence mechanisms on backfill strength and summarizes the application characteristics and limitations of existing backfill curing devices. On this basis, the paper introduces the in-situ environmental physical twin testing apparatus for mine backfill developed by the BGRIMM Technology Group. This apparatus precisely simulates the temperature, pressure, and pore water pressure curing conditions of the actual mining environment in a laboratory setting. It enables quantitative research on the effects of multiple in-situ environmental factors on the mechanical properties of CPB, providing critical experimental support for optimizing mine backfill mix designs.

With the gradual depletion of shallow open-pit iron ore resources, the transition from open-pit to underground mining has become an inevitable choice for sustainable development in metal mines. The determination and monitoring of rock strata movement areas during backfill mining of thick and large ore bodies are critical to mine design. Using a large open-pit to underground iron ore deposit mined by backfill methods as an engineering case study, this research systematically investigated methods for determining and monitoring rock strata movement areas through laboratory mechanical tests and numerical simulation. Three levels of rock movement ranges and monitoring zones were established based on surface deformation indicators, total displacement values, and designed movement angles. An integrated three-dimensional monitoring methodology was proposed, combining surface monitoring technologies (level gauges, GPS, and D-InSAR remote sensing) with underground monitoring points deployed in roadway engineering. The study revealed the movement patterns of rock strata during the backfill mining process: a movement arch formed after deep-level mining and backfilling, which evolved into an open barrel-shaped movement zone characterized by a “wider lower part and narrower upper part” as mining advanced toward the surface, eventually transforming into a hyperbolic barrel- shaped movement zone with a “wider lower part, narrower middle part, and wider upper part” when mining approached surface levels. Under the support of backfill and pillars, the movement angles of the hanging wall ranged from 85° to 89°, while those of the footwall ranged from 58° to 90°. After pillar extraction and backfilling, the movement angles of the hanging wall measured 64° to 77°, and those of the footwall measured 43° to 89°. The research results provide significant guidance for mine design under similar geological conditions.

Mining kimberlite deposits in Arctic environments presents unique logistical and environmental challenges, particularly due to the reliance on cement for backfilling, which is costly to transport and environmentally damaging. As an alternative, frozen zero-cement backfill has been proposed to enhance shaft stability while reducing ecological impact. This study employs finite element modeling to evaluate the geomechanical performance of backfilling within the vertical cutter mining (VCM) method, focusing on single shaft and multi shaft configurations at three spacings (6, 10, and 14 m). Comparisons between unfilled shafts (Case One) and backfilled shafts (Case Two) reveal that backfilling consistently reduces stress and strain magnitudes, with von Mises stress and volumetric strain lowered by nearly 50% relative to unfilled conditions. The stabilizing effect was most pronounced at the tightest spacing, where unfilled shafts produced stress levels up to 1.5 times higher than the single shaft baseline. Backfilling also altered failure mechanisms, shifting the depth of instability from shallow zones at –213 m in unfilled shafts to depths approaching –400 m across all spacings. These findings demonstrate that backfilling not only restrains deformation but also delays or prevents failure, enabling denser shaft layouts without compromising geomechanical safety. From an operational perspective, systematic backfilling emerges as an essential stabilizing measure, allowing Arctic kimberlite mining to balance ore recovery with excavation stability and environmental responsibility.

This paper presents laboratory- and full-scale optimisation of cemented paste backfill (CPF) at the Čukaru Peki mine, Serbia, operated by Zijin Mining. The backfill system combines waste rock and cemented paste to achieve high transportability, penetration into rockfill, and reliable strength development. Two tailings streams—dry excavated tailings from Veliki Krivelj and fresh tailings from Čukaru Peki—were investigated. Laboratory testing included material characterisation, rheology, unconfined compressive strength (UCS), and screening of chemical admixtures. Selected admixtures were subsequently evaluated in full-scale underground trials. Results demonstrate that admixtures significantly improve flowability, enable higher solids content, reduce water and cement demand, and increase UCS relative to control mixes. Cement reductions from 20% to as low as 16%–17% were achieved in laboratory scale testing while maintaining or improving mechanical performance. Further optimization achieved in full scale testing. Additional benefits include reduced water consumption, increased underground tailings placement, and a lower carbon footprint. The study confirms that chemical admixtures are an effective tool for improving CPF performance, reliability, and sustainability in large-scale mining operations.

Underground reticulation networks for paste backfill systems must hydraulically connect a single paste plant to hundreds or even thousands of stopes. These networks are composed of boreholes linking underground drives and intra-level pipes. The positioning of boreholes and routing of intra-level pipes is a fundamental design decision that directly influences both the operability and cost of the backfill system. The hydraulic route from plant to stope constrains the paste to a feasible rheology window. Rheology is principally controlled by the CPB solids concentration, which in turn affects the geotechnical properties of the cured paste. Suboptimal route design can therefore result in (1) a narrow or even non- existent operating window, making consistent delivery difficult, or (2) reduced solids concentration, which increases binder demand and raises the unit cost of the backfill. In a study conducted by Retic Systems for an underground operation, an algorithmic design approach was developed to optimise reticulation layout and achieved a 13% reduction in binder usage. The process involved converting spatial mine design data into a graph representation and applying a heuristic graph traversal algorithm iteratively to construct routes for each stope. Graph edge costs were defined as a combination of CAPEX (pipe procurement and installation) and OPEX (binder consumption). The traversal algorithm was adapted from A* search: during each frontier update, route hydraulics were evaluated to (1) determine the required pipe class and (2) ensure that line pressures remained within minimum and maximum tolerance limits. The iterative nature of the approach allowed optimization of shared infrastructure between stopes, with core reticulation sections re-evaluated as new connections were added. This enabled minimization of life of mine costs while maintaining hydraulic feasibility across the network.

The sustainable stabilization of underground mine voids remains a critical challenge, as extensive coal extraction continues to underpin industrial and economic growth. Conventional backfilling materials such as river sand are increasingly scarce due to environmental degradation, urbanization, and restrictions on sediment extraction. This study develops a novel sustainable lightweight aggregate (SLA) synthesized from fly ash (FA) and waste plastics as a binder, aimed at addressing both material shortages and solid-waste management issues. The fabricated SLAs were physically and mechanically characterized to assess their suitability for hydraulic backfilling applications. Results reveal that the SLAs possess significantly lower relative density than raw FA, improving their transport efficiency through pipelines. Their coarse well-graded particle structure enhances pumpability, and permeability while substantially increasing shear strength compared with untreated FA. Laboratory investigations further demonstrate that when SLA backfilling is applied around coal blocks, the load-bearing capacity improves by up to 37% at a 90% coverage ratio relative to unfilled conditions. These findings confirm that SLA is a technically viable, environmentally beneficial, and operationally efficient material for mine backfilling. The work promotes the dual advantage of utilizing industrial FA and disposable plastic waste while contributing to safe mining operations and broader sustainable engineering practices.

Paste backfill is typically delivered over long distances ranging from 1 -5 km or even further in some cases. The ability to deliver paste backfill either by pumping or via gravity flow depends on the ability to control friction losses in the pipeline which are primarily governed by the paste viscosity. In addition, the paste backfill strength is highly sensitive to the water/cement ratio and since higher water content results in a lower viscosity for a given backfill material. The control of the viscosity is important to control the consistency of the backfill strength. Despite the paste backfill viscosity control being very important for strength and delivery to the stopes, the control of backfill viscosity is frequently not as accurate as it could be. This is despite the fact that improvements in viscosity control are frequently not difficult to implement even in existing systems that do not have good viscosity control. This paper presents various methods to control paste backfill viscosity and their associated control system and equipment specification requirements. Some typical impediments to viscosity control such as adverse material properties, process design decisions and inadequate equipment selection will be presented as well as solutions to improve viscosity control in new and existing systems.