Publications

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.

Accurately predicting the geochemical behaviour of underground backfill is essential for designing effective closure strategies and reducing long-term water management risks. This case study describes a novel approach to predict geochemical source-terms for paste backfill in an underground nickel mining operation based in Tanzania, completed as part of a Definitive Feasibility Study (DFS) assessment. The backfill material, referred to as paste aggregate fill (PAF), comprises sulphide-bearing tailings, crushed waste rock, process residues, and a slag-based cement binder with a process-derived binder aid. Source terms were derived to quantify post-closure solute mass loadings to groundwater, under submerged conditions, to inform predictive groundwater modelling and closure planning. A conceptual framework was developed to represent the flow and geochemical processes influencing solute release from the PAF, focusing on two mass transfer mechanisms: advection and diffusion. Laboratory testing provided the empirical basis for the modelling reducing the requirement to apply scaling factors. Modified triaxial permeability (MTP) tests were used to estimate advective porewater quality, while the Leaching Environmental Assessment Framework (LEAF) method was applied to derive diffusion coefficients. Source terms were generated for both long-term (base case) and initial flushing (upper case) conditions, with simplifying assumptions applied to address uncertainty and maintain conservatism. Results show that the PAF shows low hydraulic conductivity limiting advective mass transfer, high initial alkalinity, and a calcium–chloride dominated leachate. The upper-case scenario predicts elevated concentrations of certain metals, including copper, strontium, and sodium, during the early flushing period, with concentrations decreasing over time in line with ordered-rate kinetics. Diffusivity values are relatively low, with the highest observed for aluminium, cobalt, lead, and vanadium. This work demonstrates a novel, structured laboratory-informed approach to source term derivation for paste backfill, transferable to other mining operations requiring assessment of long- term water quality impacts from underground backfill disposal.

To achieve efficient resource utilization of bulk industrial solid waste, this study employed hydrothermal synthesis and low-temperature calcination to prepare coal gangue cementitious materials (CGCM). The effects of hydrothermal temperature (A), Ca/Si molar ratio (B), NaOH content (C), and calcination temperature (D ) on the properties of the materials were investigated using an orthogonal test, with the 28-day mortar compressive strength serving as the key evaluation index for range analysis. The results show that the significant order of the influence of various factors on the compressive strength is as follows: calcination temperature (D) > Ca/Si molar ratio (B) > hydrothermal temperature (A) > NaOH content (C). The optimized process parameters are as follows: hydrothermal temperature of 90 °C, Ca/Si molar ratio of 2.0, NaOH content of 1.5%, and calcination temperature of 800 °C. Under this condition, the 28-day compressive strength of the prepared cementitious material reached 19.3 MPa. Based on the conclusion of the orthogonal experiment, the evolution mechanism of calcination temperature and Ca/Si molar ratio on the microstructure and properties of the material was studied. Calcination at 800 °C is beneficial for the formation of highly active phases, such as β-C2S, α′-H-C2S, CA, and C12A7. At 1,000 °C, a large amount of inert phase C2AS) is formed, resulting in a significant decrease in strength. The Ca/Si molar ratio directly affects the production of active minerals by regulating the degree of polymerization of silicon-oxygen tetrahedra. Conductivity and pH tests further confirmed that the sample calcined at 800 °C showed the best ion dissolution rate and pozzolanic reactivity, which provided a theoretical basis for strength development. This study offers a high-value utilization pathway for coal gangue, elucidating the micro-level mechanisms of key parameters to support its application in mine backfilling.

A reasonable evaluation on required strength of side-exposed backfill is significant for safe and economic mining in open stoping with subsequent backfill. The backfill stress distributions and contact properties between backfill and rock should be considered in the evaluation method. In this study, analytical models for arching stresses of uncemented backfill in secondary stopes and side-exposed cemented backfill in primary stopes have been proposed respectively. The analytical stresses have been verified against numerical outcomes by FLAC3D simulations. In addition, the lateral pressure from uncemented backfill acting on backside of side-exposed cemented backfill, and frictional resistances along-side walls between backfill and rock have been investigated to reveal contact mechanism and influences on the stability of exposed cemented backfill. Based on potential failure modes of exposed backfill which are quantitatively characterized by direction angles of sliding plane and frictional forces along side interfaces between backfill and rock, an analytical model for required strength evaluation have been proposed. Numerically searched strength requirements under different stope sizes (length, width, height) and backfill parameters (bulk density, internal friction angle) have been used to verify the analytical solution. Then, the analytical and numerical solutions show the best consistency when direction angle of sliding plane α =45°+fc/2 and direction angle of frictional resistances β =45°‒fc/2. The analytical model has been obtained to evaluate the theoretical required strength of side-exposed cemented backfill. Furthermore, the method to transfer the theoretical required strength of backfill to practical required strength by the floating factor of safety is discussed.

The filling mining method is a core mining approach for deep and high-risk ore bodies. However, the filling slurry often fails to effectively reach the roof due to issues such as water seepage and settlement, and an insufficient roof contact rate can lead to safety hazards such as roof collapse. The existing forced roof contact technologies have issues such as complex processes and limited effectiveness. Therefore, a new “active roof-contact” filling concept is proposed. The core principle of this concept is to introduce special chemical reaction-based solid phase expansion components, which induce controlled volume expansion of the filling material through hydration reactions. This will drive the filling body in the local uncontacted areas to actively “fill in”, thereby significantly improving the roof contact effect. During this process, the continuously developing expansion force can also act on the rock interface to form a “pre-stress field”, improving the secondary stress concentration of the surrounding rock. This study takes the cemented filling body of all tailings and waste rocks as the main research object, analyzes the expansion mechanisms of three different types of chemical reaction-based solid phase expansion agents. Then, through the grey target decision-making method, with strength as the benefit type index, slump, final vertical expansion rate and lateral expansion stress as the cost type index, an optimization decision is made to ultimately select the expansion agent suitable for mine filling and its optimal level, to provide a useful reference for future research on active roof-contact backfill(ARCB) materials.

The rock-backfill composite structure is the core load-bearing structure formed by the stage open stope subsequent filling process in underground metal mines. As a key or even permanent stope component, its bearing capacity and stability directly determine the ground pressure control effect during mining and long-term stope stability, which is of great significance for ensuring safe and efficient mining. Due to significant differences in medium characteristics and mechanical properties between rock and backfill, this composite structure’s damage evolution and failure laws differ notably from single- medium structures, and relevant research holds important scientific value and engineering practical significance. This paper systematically reviews global research progress on the mechanical properties, damage mechanisms, and synergistic bearing mechanisms of multi-medium composite models. It first outlines the mature research system and methodological references of coal-rock composite structures, then focuses on sorting out rock-backfill composite structure research findings from both macro and meso-micro scales. At the macro scale, laboratory mechanical tests and numerical simulations such as finite element method and finite difference method clarify the composite ′s synergistic pressure-bearing characteristics, stress-strain laws, and failure mechanisms. At the meso-micro scale, observation technologies including computed tomography scanning, acoustic emission, and discrete element numerical simulation reveal the damage essence such as pore development, micro-crack propagation and particle interaction imbalance. Compared with the comprehensive research on coal-rock composite structures, rock-backfill composites still have deficiencies in dynamic mechanical properties, macro- meso-micro cross-scale correlation, and parameter quantitative characterization. Based on this, the paper looks forward to future research trends of rock-backfill composite structures. The research results not only support supplementing the interaction mechanism between backfill and surrounding rock and enriching the meso-micro mechanical theory system of multi-medium models but also provide reliable theoretical basis and technical reference for mine stope structure optimization, filling ratio design, and long-term stability guarantee.

In India, several underground coal mining operations exist beneath essential surface infrastructures such as railways, highways, and urban settlements. Many of these mines, developed at relatively shallow depths, have left behind abandoned workings under railway corridors, posing a significant risk of subsidence and surface collapse. Such instability can threaten railway track integrity, passenger safety, and transport continuity. To address this critical issue, a pilot-scale experiment on self-levelling paste backfilling was conducted in a coal mine in Jharkhand, India. The paste, prepared using a blend of fly ash, cement, chemical additives, and water, exhibited favorable flow and self-levelling characteristics during underground placement. Moreover, it developed sufficient compressive strength to stabilize overlying strata. The promising results underscore the effectiveness of self-levelling paste backfill as an innovative and practical solution for mitigating subsidence hazards beneath vital railway infrastructure.

With the growing emphasis on carbon peaking and carbon neutrality, red mud has garnered significant attention as a promising backfill material due to its potential in strength optimization and heavy metal control. This study systematically investigates the mechanical properties and heavy metal leaching behavior of red mud-based backfill materials. A combination of macro-scale experiments—such as setting time, bleeding rate, flowability, and unconfined compressive strength (UCS)—is performed alongside micro-scale analyses, including X-ray diffraction (XRD), scanning electron microscopy (SEM), and leaching toxicity tests. Results demonstrate that, with 60% red mud content, the setting time, bleeding rate, and flowability initially increase before declining. A moderate red mud addition accelerates UCS development due to the synergistic effects of minerals (e.g., SiO₂ and Al₂O₃) during hydration, promoting the formation of hydration products. However, excessive red mud content reduces UCS, particularly in samples with 70% red mud, where the 28-day UCS is only 82.64% of the 7-day UCS. Further analysis reveals that at 60% red mud, the quantity and microstructure of primary hydration products (e.g., calcium aluminate hydrate and C-A-S-H gel) are significantly enhanced, and the pore structure is optimized. Moreover, the heavy metal leaching concentration in the red mud- based backfill materials is below the detection limit for Class Ⅲ groundwater as per GB/T 14848 — 2017. These findings highlight the potential of red mud-based backfill materials as a sustainable solution for mine waste utilization, offering both environmental benefits and resource efficiency in mining operations.

In response to the carbon neutrality goal, the field of deep metal mine backfilling urgently needs to seize the transformative opportunity for green and low-carbon development. It is critical to fully utilize the carbon storage space within underground goaf and the solid and gas waste generated during mining operations. Accordingly, this study focuses on the mineralized cemented paste backfill (MCPB) and aims to elucidate the characteristics of the hydration–mineralization synergistic reactions and the evolution of macroscopic mechanical properties. Scanning electron microscopy (SEM) and mechanical testing were comprehensively employed to conduct investigations into hydration–mineralization products and mechanisms, damage characteristics, as well as carbon sequestration performance. (1) Morphological analyses of hydration–mineralization products were performed based on SEM–EDS, revealing the synergistic mechanisms of hydration and mineralization in MCPB. (2) Fracture modes were identified and established, showing that MCPB specimens mainly undergo shear failure. And most of the specimens showed shear failure accompanied by secondary shear cracks and secondary tensile cracks. (3) Thermogravimetric analysis was employed to determine the carbonation rate and carbon sequestration performance of MCPB.

With the increasing demand of mineral resources, the stage subsequent backfill mining method is widely used in various mines with the advantage of its high production capacity, and it is easy to form a large-scale empty area in the process of this mining method, resulting in the filling method of mines is mostly layered filling. Layered filling has a certain effect on the physical properties of the cemented tailings backfill(CTB) and the stability of the quarry, therefore, this paper uses indoor experiments to study the effect of different factors on the physical properties of the layered CTB, and uses numerical simulation to simulate the stability of the quarry under the influence of different layered variables under the actual size, and obtains the following results: (1) the experimental results show that the increase of the number of layers, the height ratio, and the reduction of the layered gray-sand ratio will weaken the strength of the layered CTB, and the layered CTB will be stronger than the layered CTB. The uniaxial compressive strength of layered filler is polynomial in function of the number of layers, polynomial in function of the height ratio, and multiplicative power in function of the gry-sand ratio. (2) Numerical simulation results show that with the increase of the number of layers, layer height, and layer angle, the maximum principal stress of the quarry increases continuously, which makes the ore rock bear more stress and harms the stability of the quarry.

This study investigates the settlement and shrinkage behavior of high-concentration filling slurry under occluded conditions, with the objective of improving the efficiency and reliability of backfill operations in underground mining. Large-scale concrete or slurry placement projects often experience variations in physical and chemical properties due to environmental changes, which can significantly influence material performance. To address this, both macroscopic and microscopic analyses were conducted to evaluate settlement patterns, concentration regulation, and the effects of different sand- to-cement ratios. The results indicate that the

Recycling cement-amended waste tailings into mined-out cavities has yielded significant financial and environmental benefits for the mining industry. Once in place underground, the backfill mass is supported by retaining structures across the access tunnel, with the resulting earth pressure critically influencing the stability of the subsurface minefill system. Despite its substantial socioeconomic benefits, recent field operations have encountered challenges due to anomalous minefill pressure, stemming from an unidentified source of thermal loading. As mining depths increase, interacting with hostile geothermal environments, this pressure anomaly becomes a crucial issue that must be addressed to enable clean and sustainable mine development in unprecedentedly challenging conditions. In this paper, we explore the multiphysics origin of this anomalous thermal pressure and discuss its practical implications for future mine backfilling. We then present a comprehensive review of existing experimental and computational studies on multiphysics minefill behaviour under complex heat loads. By critically identifying current knowledge gaps, we provide guidance for future research aimed at enhancing the safety and cost-efficiency of waste tailings recycling in challenging mining environments.

The mechanical response of cemented tailings rock backfill (CTRB) in underground mining environments is significantly affected by environmental temperature, yet the coupled effects of thermal loading and damage evolution are not fully understood. In this study, a three-dimensional meso-scale numerical model of CTRB is established using the coupled thermal-displacement analysis to investigate the influence of temperature on mechanical behaviour and internal damage evolution. The model explicitly accounts for the mechanical heterogeneity of aggregates, mortar, and the interfacial transition zone (ITZ). Specimens conditioned at different temperatures ranging from 20 ℃ to 50 ℃ are subjected to quasi-static uniaxial compression. The results show that (1) increasing temperature leads to a gradual reduction in peak stress and a corresponding increase in deformation capacity, while the elastic modulus is only slightly affected; (2) compared with the reference specimen without thermal coupling, temperature-conditioned specimens exhibit smoother strain distributions and higher local stress levels along internal paths, which can be attributed to thermal expansion and enhanced stress redistribution; (3) damage evolution analysis indicates a clear transition from localized damage concentration to more distributed damage patterns as temperature increases, resulting in earlier damage initiation but more gradual failure development. These findings demonstrate that the thermo-mechanical response of CTRB is governed primarily by damage evolution and stress redistribution. The coupled thermal-displacement approach is shown to be effective for capturing temperature-induced effects on CTRB behavior.

The intervening pillar plays a significant role in ensuring safety and ore recovery efficiency during sequential stope-and-fill mining. Its mechanical behavior, however, is strongly time-dependent due to the coupled effects of rock creep and backfill consolidation, which are often overlooked in conventional design. This paper presents a numerical model based on FLAC3D that explicitly incorporates these time-dependent processes to investigate pillar performance under varying stope sequencing intervals. The results show that a short interval allows the partially consolidated backfill to provide effective lateral support when the adjacent stope is excavated, enhancing pillar stability. A longer interval permits further rock creep and backfill densification, leading to significant swelling pressure on the inner side of pillar. This induces a beam-like bending and an asymmetrical stress state including tensile minimum principal stress in the outer part of pillar and high differential stress with elevated brittle shear ratio in the inner portion. Results also suggest that wider pillars exhibit markedly better resistance to both tensile spalling and shear damage, whereas narrow pillars are highly susceptible to instability as stope sequencing interval increases. The findings underscore that managing sequencing interval and optimizing appropriate pillar width are critical for mitigating time-dependent risks of pillar in multiple stope-and-fill operations.

Paste backfillinging is a central development direction for the construction of green mines, offering a high tailings utilization rate, reducing the cement consumption quantity, and keeping the minging operations safe. However, the performance regulation in high-solids backfilling slurry systems remains a critical bottleneck that limits the large-scale engineering application of paste backfillinging, and the admixtures represent key technical routes to overcome this barrier. This paper systematically reviews recent advances of admixtures in the concrete-related engineering that may be applied in paste backfillinging. Firstly, a classification framework of admixtures used in concrete and paste backfillinging was established and their mechanisms of performance regulation and applicable scenarios were clarified. And then, the mechanisms of contemporary admixtures to improve flowability of backfilling slurry and to enhance the strength of backfilling body were examined. The typical engineering problems were summarized, and the outstanding challenges in adaptability to complex and extreme field conditions and in coordinated multi-objective performance regulation were identified. Finally, three promising development directions of the admixtures used for paste backfillinging were proposed, i.e., environmentally friendly chemistries, enhanced adaptability to extreme or complex operating conditions, and synergistic fluidity–strength optimization strategies. The study provides a systematic conceptual framework to guide the efficient development and engineering deployment of paste backfilling admixtures.

Newmont Goldcorp Australia’s Tanami Operations consists of the Dead Bul­ lock Soak underground mine (DBS) and the Granites Processing Plant. The Backfill Group at DBS has recently introduced a number of improvements to benefit the UG reticulation system. These improvements focused on three areas: reduction of major blockage downtime, continuous monitoring of tight filling operations, and paste plant automation. The first part of the paper will cover the installation of dump/diversion valves throughout the DBS reticula­ tion system. This paper will present why these valves were installed, the design behind deter­ mining where they were placed, and several case studies showing how their installation has benefited DBS. The second part of the paper will detail the changes that allow for continuous monitoring of tight filling and present case studies on how this has benefited DBS. The third part of the paper present the results of a trial paste plant automation project which was run in conjunction with NGA’s Process Control Group. This section will detail how this automation works and present case studies on how this automation has benefited DBS.

Mine backfill is typically placed in stopes with drawpoints or access drifts at the bottom of the stope. To contain the fluid backfill, barricades are required to prevent the flow of backfill out into the access drift. Typically barricades are constructed of muck or reinforced shotcrete; however, there are some disadvantages with typical barricade design and this paper examines some theoretical possibilities for a new barricade design that may improve safety, productivity, cycle time and the mines economics.

Prior to backfilling, fibrecrete barricades (which for the purpose of this paper refers to both barricades and bulkheads utilised for Minefill purposes) are typic­ ally cured to achieve a target strength. However, due to sensitivity of early age fibre­ crete strength caused by variations in mix properties, curing environments and spraying techniques, the rate of strength development can be quite varied. Challenges associated with conventional curing, coring transportation, and destructive strength testing methods and mine location generally prevent early age quality control testing of fibrecrete barricades and the consequence is often conservative cure periods leading to extended fill cycle times. This paper further develops a novel technique where laboratory testing is used to develop a unique relationship between strength and the shear wave velocity (or small strain stiffness) of the fibrecrete. The inves tigation considers a range of different vari­ ables encountered during the manufacture of fibrecrete to illustrate the unique relationship. The presented non-destructive test method provides a practical method to define the rele­ vant barricade strength and shear wave velocity relationship. Implementation of improved quality control techniques such as that proposed can reduce fill cycle times without comprom­ ising safety.