Publications

Addressing the technical challenge of coordinating safety and efficiency in the mining of gently dipping, thin orebodies, this study—using the Chengcheng Mine as the engineering context—conducts an end-to-end investigation covering mining-method selection, stope structural design, stoping process planning, backfill system construction, and mix-design optimization. By introducing a time- dependent stability coefficient and revising the hydraulic-radius calculation model for point-pillar stopes, we extend the classical Mathews stability graph method to enable safe stope-parameter design. The required backfill strength and thickness are determined using the Pakalnis empirical analogy method. Aggregate gradation measurements and backfill mix tests are performed to build a random forest (RF) strength-prediction model, which quantifies the significance of aggregate gradation, slurry concentration, and cement content on backfill strength. Furthermore, a random fores-differential evolution (RF-DE) coupled inversion model is established to achieve intelligent search of mix designs that meet target strengths. Engineering practice demonstrates that the proposed workflow effectively resolves the key issues of safe and efficient extraction for the gently dipping thin orebody at this mine: stope production capacity reaches 150 t/d, ore loss and dilution are controlled within 12% and 10%, respectively, and China′s first underground backfill mixing station has been constructed—providing technical support and practical experience for economically viable development under similar geological conditions.

A significant percentage of power production in the country is still dependent on thermal power plants that use coal as their fuel, which has led to massive production of fly ash as an industrial by-product. Disposing fly ash and especially the storage of ash in an ash pond has become a major environmental and operational challenge facing thermal power stations. Simultaneously, the growing need in sand and aggregates in construction, roads, and geotechnical practices has caused faster exploitation of natural resources. In that regard, the current research examines how alternative aggregates can be developed by applying different percentages of fly ash and plastic waste. The environmentally hazardous plastic materials were obtained as municipal solid waste streams and added to encourage resource recovery and waste valorization. The two-fold environmental advantages of using fly ash and plastic waste as constituents of aggregates relate to the lightness of their disposal and the reduction of reliance on natural aggregates. The fly ash plastic aggregates were formed by the rotary extruder into seven mix proportions. The slake durability and point load strength index tests were used to compare the engineered aggregates in terms of durability and mechanical performance, respectively. Moreover, the essential physical and geotechnical characteristics were calculated and identified and compared to the values of fly ash alone to evaluate the impact of plastic inclusion. The study show that the addition of plastic increases the durability of the aggregates and has a positive effect on their physical and geotechnical properties, which implies that the derived synthetic lightweight aggregates could be useful in hydraulic backfilling works in underground mines.

The paper considers the methodology for a comprehensive analysis of the stability of an open pit- dump system, using limit equilibrium (LEM) and finite element (FEM) methods in the Russian CAE (computer-aided engineering) software Fidesys. It briefly highlights the issues of comparing limit equilibrium methods using the VNIMI (Research Institute of Geomechanics and Mine Surveying- Intersectoral Scientific Center “VNIMI”) methodology and a specialized software product with numerical methods. The main focus of this study is to compare the results of the stability analysis in the volumetric model of the open pit-dump system using limit equilibrium and finite element methods in the CAE software Fidesys. It was found that, when modeling the combined operation of an open pit-dump system in complex terrain, both methods should be used, as each has its own advantages. The finite element method, for instance, has certain features that are not present in the calculations using the limit equilibrium approach. As a key scientific contribution, this paper introduces an automation program for calculating the stability of open-pit walls using the limit equilibrium method in CAE Fidesys, which was not previously integrated in the original software. The calculations performed with the use of this newly developed module were compared to those obtained from other widely used software solutions available on the market. The findings demonstrate a remarkable level of convergence in the calculation results for all relevant parameters, including the safety factor, localization, instability type, and deformation. The proposed approach improves the accuracy of calculations and ensures consistency between the higher stress design zones and the actual deformation and fracture patterns. It also enhances the ability to predict the behavior of rock mass when calculating stability parameters for facilities, both during operation and design.

Conventional sensors for cemented paste backfill (CPB) monitoring often fail due to three dominant process challenges: excessively high slurry concentration, material inhomogeneity, and partially filled pipe flow. While visual monitoring offers a promising alternative, its practical implementation is critically hindered by the fundamental need for extensive data annotation. We present a weakly supervised, vision-only framework that enables robust concentration estimation in backfill mixing tanks without human annotations. A large vision-language model (LVLM) performs pairwise ranking over unlabeled video clip pairs to compare relative paste concentrations and produce confidence- weighted ordinal labels. These signals are distilled into a compact vision model that runs on an edge device and directly infers paste concentration, requiring only sparse solid concentration measurements for calibration. Our results indicate that LVLM-derived ordinal judgments effectively transfer high- level semantic reasoning into quantitative material characterization, enabling specialized models for backfill operation to achieve a mean absolute error (MAE) of 2.12% in concentration. Despite harsh plant conditions and illumination variations, the distilled model achieves high accuracy via vision-only inference, supporting instrumentation and control tasks such as concentration control, binder dosage control, and water-cement ratio optimization. This establishes a foundation-model-supervised pathway for non-intrusive CPB sensing that reduces instrumentation burden and facilitates integration with backfill production, quality control, and placement workflows.

Backfill reticulation systems - whether for paste, hydraulic fill, or cemented rock fill (CRF) - rely on multiple functions including switching between pumps, directing flow to boreholes, initiating flush water or high-pressure injection, and managing emergency dumps. In many mines these tasks remain manual, requiring crews to physically move heavy elbows and spools. This not only slows routine operations such as daily pouring or flushing, but also exposes workers to risk in high-pressure, high- wear environments where it is often difficult to ensure a true zero energy state (ZES), particularly during blockages. In emergencies, manual reconfiguration creates not only critical delays but also serious safety hazards; workers must intervene under pressure and in confined spaces at the very moment conditions are least predictable. If response is slow, paste may cure in the line, resulting in costly downtime and infrastructure damage. Integrating automation-ready diverter valves at the paste plant transforms both routine and emergency operations. For daily use, operators can remotely and instantly redirect flow, switch boreholes, or initiate flushing without underground intervention—eliminating hours of manual handling and reducing non-productive time. In emergencies, a dynamic decision tree provides a structured, rules-based matrix for operators to follow. By laying out clear actions based on pressure readings, flow behavior, and whether flushing restores clear water at pour points, the decision tree removes guesswork and reduces human error, ensuring consistent responses regardless of operator experience. When paired with remote valve actuation, this framework enables rapid interventions such as pump switching, initiating high-pressure water injection, or diverting flow to pour points and dumps. The result is lower personnel exposure, faster recovery, and protection of the reticulation system against permanent damage. This paper will discuss how automation at the surface paste plant - combined with a structured emergency decision tree - creates a safer, more consistent, and more reliable foundation for backfill operations. Using real-world examples, we will demonstrate how diverter valve automation and operator decision matrices can work together to protect people, reduce financial risk, and ensure the long-term stability of backfill reticulation systems.

Increasingly stringent environmental regulations, both in Germany and across the European Union (EU), are limiting or prohibiting the above-ground disposal of certain industrial (non-mining) chemotoxic wastes. As a result, alternative, sustainable disposal routes are gaining importance. Over the past three decades, K-UTEC AG (K-UTEC) has supported mining operations in utilizing underground cavities not only for conventional backfilling but also for the controlled and legally compliant disposal of chemotoxic non-mining waste. In many cases, these wastes contribute to cavity stabilization and are kept safe in terms of long-term environmental safety, making such projects technically and economically viable. The legal framework in Germany and the EU is outlined, distinguishing between pure disposal and waste utilization as a substitute for primary raw materials in backfill applications. The advanced and well-established European standards could serve as a model for international adoption. Feasibility assessments must always be site-specific, considering factors such as hydrogeology, cavity geometry, logistics and the availability of suitable wastes. Current practices have identified promising waste streams, e.g., from incineration, steel production, cement manufacturing, and waste treatment, that are both suitable for underground use and economically attractive due to limited disposal capacities. A forward-looking approach to mine backfilling is presented, showing how underground cavities can become valuable assets in industrial waste management. K-UTEC anticipates growing international relevance for this dual-purpose strategy.

The design of underground reticulation networks for paste backfill systems is typically achieved through the use of steady state hydraulic models. These lightweight models use pipe spatial data, class ratings, and pressure loss equation to calculate line pressures and tolerances. During design, variables such as flowrate, solids concentration, or plant discharge pressure can be adjusted to assess system performance. However, a fundamental simplification is that paste material is assumed to be homogeneous from source to discharge. In practice, variability in paste composition, driven by plant proportional-integral-derivative (PID) control loops or fluctuations in tailings feed, introduces significant dynamic effects. This paper introduces a discrete time simulation (DTS) framework to more accurately model pressure loss in heterogeneous paste flows. The study evaluates three key aspects of DTS implementation: representation of process variance, choice of pressure loss models, and reticulation control philosophies (e.g., fixed discharge pressure, fixed flowrate, or differential pressure control). Machine learning approaches (neural networks) are compared directly with empirical numerical models for predictive accuracy. Results highlight the limitations of steady state models, particularly in systems with high variance where line pressures can deviate markedly from steady state predictions, leading to risks of over pressurisation or slack flow. DTS provides a more realistic representation of network hydraulics, offering a robust alternative design methodology for complex backfill systems.

This paper presents the commissioning experience and binder optimization strategy implemented at the V oisey′s Bay paste backfill plant, with a focus on QA/QC data and trends in unconfined compressive strength (UCS) under evolving tailings conditions. During plant commissioning in 2023, tailings properties were found to deviate from the original design assumptions. The changes in lower specific gravity (SG) and finer particle size distribution (PSD) posed a risk of reduced backfill strength at fixed binder contents. To address this risk, the QA/QC program was optimized to incorporate routine tailings characterization and systematic UCS testing. Initial test results indicated that a binder content of 5% was required to achieve the target strength of 200 kPa at 7 days for plugs, while 4% binder was required to reach the target strength of 380 kPa at 21 days for bodies. However, these binder dosages exceeded the FEL3 design basis of 2%-2.5%. A stepwise binder reduction program, supported by UCS data from more than 2,200 cylinders collected over a three-year period, enabled a progressive reduction in binder demand to 3.5%-4.0% for plugs and 2.8%-3.0% for bodies. This corresponded to a 1% -1.5% reduction in binder consumption, equivalent to approximately 14,000 tonnes of binder savings per year, without compromising strength performance. The results demonstrate that integrating QA/QC monitoring with UCS testing provides a primary basis for optimizing binder usage under evolving tailings conditions. Ongoing evaluation of alternative binders is expected to further reduce costs and material intensity while maintaining strength reliability.

The mining industry faces severe environmental challenges, requiring economically feasible carbon sequestration pathways. Backfill materials, with their alkaline properties and large-scale application potential, serve as effective carbon sinks. However, existing research mainly focuses on carbon fixation under solid-state curing conditions, which is costly and hard to implement on-site. This study proposes direct CO₂ injection during the mixing of backfill slurry to explore the feasibility of synergistically enhancing mineral carbonation and backfill performance. Experiments systematically investigated the effects of different CO₂ mixing durations (0–100 s) under 0.5 MPa on the uniaxial compressive strength (UCS), failure mode, and microstructure of cemented tailings backfill (CTB) at a 28-day curing age. Results show that UCS peaks at 60 s with a maximum increase of 53.0%. Appropriate CO₂ stabilizes the structure, forming an orderly shear-dominated failure mode, while excessive CO₂ causes cementation failure, sharp strength decline, and brittle fracture characteristics. Microstructural analysis indicates that appropriate CO₂ promotes synergistic carbonation-hydration reactions, facilitating co-precipitation of calcium carbonate crystals and calcium silicate hydrate (C-S-H) to achieve a dynamic balance between “pore formation and cementation densification”. Excessive CO₂ leads to pore coarsening and structural damage. This study confirms that CO₂ injection during mixing simultaneously improves backfill strength and achieves carbon-negative solidification, providing a novel approach for the synergistic resource utilization of mine tailings and CO₂ waste gas in green mining.

Cemented paste backfill (CPB) is a cornerstone technology for achieving green mining. This paper presents a comparative framework. It contrasts the global perspective with Chinese innovations in CPB development. First, it reviews the evolution of international CPB technology. This includes core equipment such as the deep cone thickener (DCT), high-efficiency mixing, and piston pumps. It also covers foundational theories, such as rheology. This analysis highlights the international model’s focus on modularization and standardization. Furthermore, it provides an in-depth analysis of China’s unique CPB development path. This path was developed to address “deep, large-scale, and complex” geological conditions. It also meets the strategic demands of the “dual carbon” goals. China’s core contribution lies in systems integration—linking mining, processing, backfilling, and solid waste management. This approach emphasizes the synergistic use of multiple sources of solid waste and has spurred technological innovations to address major engineering challenges, such as thickening ultra- fine tailings and transporting them across large height differences in ultra-deep shafts. This study highlights China’s progress in CPB technology. It has advanced from “

Paste backfill performance depends on interdependent processes, yet data management is commonly split across several software tools and spreadsheets, limiting trend inference and rigorous analysis of system performance. This study presents a centralised digital platform integrating the management of several process workflows. The platform includes a QAQC database, stope fill design tools, backfill scheduling, reticulation management, and advanced analytics. Granular fill logging ties SCADA and QAQC to discrete filling events for root-cause diagnosis of process deviations and strength shortfalls. Machine-learning models trained on ingested data improve strength prediction. A digital reticulation model links stope design objects to the network with rheological parameters bound to stope design set points enabling route-specific hydraulic analysis; auto-generated bills of materials streamline installation planning; wear observations feed back to the hydraulics to plan pipe replacement. Together, these capabilities replace ad hoc tools with a coherent, evidence-led workflow. Applied at an active operation, the platform unified management and materially improved operational visibility, simplifying day-to-day control and yielding lower OPEX alongside higher design accuracy. At industry scale, adoption of centralised digital systems would standardise practice and make performance evaluation consistently data driven. Pooled cross-project datasets would support deeper analysis and more robust multi-site engineering models, advancing understanding of backfill performance, establishing shared benchmarks and building an industry knowledge base.

Coal based solid waste is one of the major industrial wastes, and its large−scale disposal and utilization are of great practical significance for the sustainable development of the coal industry and the protection of the ecological environment in mining areas. As a green mining method that combines underground disposal of coal based solid waste and “three down” coal pressure recovery, backfill mining has been rapidly developed and applied in the past 20 years, forming a technical system mainly consisting of solid and paste filling materials, and fully mechanized and continuous mining filling as the main processes. This paper summarizes the technical characteristics and classification of coal based solid waste filling and mining, represented by gangue and fly ash. The basic physical and chemical properties of solid wastes such as coal gangue, fly ash, slag, gasification slag, and desulfurization gypsum indicate that coal based solid waste has the feasibility of being used as filling materials. The compression characteristics of gangue solid and paste filling materials are summarized, and the characteristics of the two main filling and mining processes, continuous mining and charging and comprehensive mining filling, are analyzed. Prospects are made in expanding the range of coal based solid waste filling materials, improving the production capacity of filling and mining, and reducing filling costs, in order to provide ideas for the future development of coal based solid waste filling and mining.

Waste rock and tailings represent the primary solid wastes generated in metal mining. Underground co-backfilling with waste rock and cemented tailings offers an effective approach for the large-scale utilization of these materials. However, quantitative methods for characterizing the permeability and compactness of such composite backfill systems remain limited. In this study, semi-industrial surface experiments were conducted using a self-developed experimental device combined with infrared imaging technology. Three dumping sequences—waste rock followed by slurry, slurry followed by waste rock, and simultaneous dumping—and three accumulation angles of waste rock (90°, 60°, and 30°) were investigated. The compactness of the co-backfill and the permeability of cemented tailings slurry within waste rock voids were quantitatively analyzed. Results show that simultaneous dumping yields the highest compaction, although practical constraints may limit its application. Therefore, a sequence of slurry dumping followed by waste rock, at a volume ratio of 3 :2, is recommended. Moreover, the inclination angle of waste rock piles was found to be positively correlated with slurry penetration. A quantitative relationship between slurry infiltration and the contact surface area was established, expressed as the penetration volume per unit area, with values of 0.185 m³/m² and 0.107 m³/m² depending on whether the pile base was in contact with the stope boundary. Based on these findings, a co-backfilling strategy for high stopes in iron mines is proposed, providing a technical basis for the efficient utilization of mine waste through integrated waste rock–tailings backfilling.

This paper investigates the influence of mine tailing particle size and curing temperature on the rheological properties and strength development of cemented paste backfill (CPB). Laboratory experiments were conducted on CPB to evaluate their physical and mechanical behavior. A series of CPB samples with different mixture designs were prepared and cured for 28 days. The effect of curing temperature and particle size on mechanical properties was assessed using uniaxial compressive strength (UCS) tests. In addition, the influence of curing temperature (ranging from 5 °C to 50 °C) on CPB samples was studied through UCS testing. The microstructure of selected specimens was further analyzed using the mercury intrusion porosimetry (MIP) technique. The results indicate that: (i) the mechanical performance of CPB can be enhanced by reducing the proportion of fine particles in the tailings; (ii) the rate of strength gain increases with decreasing particle size, samples exhibiting faster strength development than CPB samples over the 28-day curing period; (iii) curing temperature has a significant impact on both the mechanical and microstructural properties of CPB; (iv) microstructural analysis revealed that reducing fine particles modifies pore size distribution and decreases overall porosity, thereby improving the mechanical behavior of CPB; and (v) MIP results showed that the reduction of particle size altered the microstructure, leading to a higher proportion of fine pores in CPB.

The strength assessment of cemented tailings backfill (CTB) in underground stops is a focal point of current research. However, it is challenging to render the “black box” of underground backfilling stopes transparent, due to the varying drainage conditions and curing temperatures, and the corresponding pore water saturation and degree of hydration are the key intermediate indicators for strength evaluation. This study combines ultrasonic pulse velocity (UPV) testing and computed tomography (CT) technology, along with the CTB-water characteristic curve to investigate the evolution of unconfined compressive strength and ultrasonic pulse velocity in relation to water saturation, as well as the interrelationships among these three parameters. The results indicated that water saturation exerted a significant influence on UPV , while demonstrating minimal impact on unconfined compressive strength (UCS). Both UPV and UCS increase with the increasing the connectivity of solid phase, and the relationship of UPV and UCS can be fitted by exponential. Additionally, the UPV of CTB can be markedly affected by moisture content on the hydration process and transmission path. Finally, a new insight is provided that it is possible to accurately predict the strength of CTB by UPV on the basis of eliminating the effect of water. This research contributes to understanding the propagation mechanism of ultrasonic waves in unsaturated CTB, and offering a feasible approach for predicting CTB strength and mitigating potential geotechnical hazards in underground.

Underhand cut-and-fill mining is applied in underground operations where rock masses are either weak or subject to rockburst risks under high stress conditions. In such cases, miners operate beneath a cemented backfill roof or sill mat. Maintaining its stability is crucial for the safety of mining workers and equipment. Existing analytical approaches for evaluating sill mat′s stability and strength requirements generally assume rigid and immobile rock walls. However, recent numerical simulations and field observations indicate that pronounced wall convergence induced by the excavation of underlying stopes can trigger crushing failure within the sill mat. This discrepancy suggests that the influence of wall convergence has not been adequately incorporated into current design methodologies. To address this limitation, the present study conducts a series of numerical investigations to reveal the crushing failure mechanism of sill mats subjected to rock wall convergence. Furthermore, an analytical solution is developed to estimate the minimum required cohesion (c min) of sill mat associated with this failure mode. The proposed solution is established without reliance on empirical correction factors, and its validity is verified through comparison with numerical results.

Cemented paste backfill (CPB) is receiving increasing attention in modern underground mining operations due to its dual advantages of enabling the safe storage of mine tailings and providing essential ground support. Conventionally, CPB mixtures rely mainly on Portland cement as the primary binder, a material with a high greenhouse gas footprint that accounts for up to 70% of the backfill process's total emissions. To reduce environmental impact while meeting the operational requirements of mining practices, this study investigates the use of a calcium-activated pozzolanic binder as an environmentally friendly substitute in CPB mixture preparation. The binder is mixed with gold tailings to evaluate the strength development. Silicate sands were used to modify the particle size distribution (PSD) to investigate their influence on unconfined compressive strength (UCS). The results demonstrate that Portland cement achieves relatively higher strength at the initial stage (<3 days), while the calcium-activated pozzolanic binder exhibits stronger later-stage strength development. The mechanisms governing strength development in the calcium-activated pozzolanic binder mixture are discussed in terms of average pore size and connectivity, solid-phase continuity, and particle coating quality. Microstructural observations suggest that these differences are related to pore structure, matrix continuity, and particle coating quality. The findings of this study suggest that calcium-activated pozzolanic binders are promising low- carbon alternatives for CPB, providing satisfactory mechanical performance while improving the sustainability of backfilling operations.

To solve the engineering challenges of low consolidation speed, low backfill strength, and high cement consumption of ultra-fine unclassified tailings backfill in metal mines, the physical and chemical properties of various solid wastes around the Jinchanghe polymetallic mine were tested. An orthogonal test was designed for the composition of a new cementitious material to determine its optimal mixture ratio, which consist of blast furnace slag, gypsum, lime and activator. The strength growth mechanism of the new cementitious material backfill was revealed through the coupled characterization of scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) microtests. Mine field test results indicate that the in-situ coring backfill with the new cementitious material is complete and the cementitious performance is good. After 38 days of curing, the strength of the samples with the new cementitious materials can reach 3.89 MPa, which is 2.78 times that of the cement-cored backfill, and to meet the strength design requirements for backfill, the cement-tailings ratio at the bottom of the stope is reduced from 1 :6 to 1 :7, resulting in a 30% cost reduction. The research findings provide a reference for the development of new cementitious materials for ultra-fine unclassified tailings backfill in metal mines.

In underground mining with backfill, evaluating the minimum required strength of side-exposed backfill is a routine work for mining or backfill engineer. An analytical solution proposed by Mitchell and coworkers in 1982 is largely used. Since 2012, Li and coworkers have published several improvements to the original Mitchell 1982 solution after taking into account several limitations identified in the Mitchell 1982 model. In addition, Liu and coworkers have shown that the Mitchell 1982 solution was developed for short-term stability analysis, implicitly considering the backfill under an unconsolidated and undrained condition. For backfill after a prolonged period of curing, the Mitchell 1982 solution should not be suitable. The improved solutions of Li and coworkers should seem to be used. However, the improved solutions of Li and coworkers have never been validated by experimental results for side-exposed backfill under different conditions. To fill this gap, a series of box instability tests were conducted using an uncemented paste backfill to experimentally validate the analytical solutions of Li and Aubertin (2012, 2014) and Li (2014a) under high aspect ratio geometry and undrained conditions for short-term stability analysis. The measured unconfined compressive strength (UCS) values were used to calibrate and predict backfill behavior through comparison with analytical results. The results indicate that the new analytical solutions, which incorporate realistic boundary and interface conditions, provide a more accurate and representative estimation of short-term backfill stability than the original Mitchell et al. (1982) formulation. In this article, the laboratory tests and the comparisons between the experimental results and analytical solutions will be presented and discussed.

At Olympias Underground Mine, drift-and-fill mining under cemented paste backfill is required for the safe and effective recovery of sill pillars within complex geology and variable ground conditions. Cured cemented paste backfill provides critical confinement to the surrounding rock, enabling controlled blasting and reducing the risk of instability during mining. This case study reviews operational practices and design considerations specific to Olympias Mine, including geomechanics and geotechnical aspects of mining with paste backfill, paste fill strength requirements and quality control, curing times, blast sequencing, and integration of ground support systems.