Publications

Cemented paste backfill (CPB) is the emerging trend in integrated mine tailings management. CPB consists of mine tailing, binder agents, and water that provides ground support for underground openings known as stopes. CPB has tight characteristics and a very high delivery rate compared to other backfilling materials such as rockfill. Once placed in a stope, CPB is generally considered as a loose, saturated granular soil at its early stage of binder hydration. In this state, CPB might be prone to liquefaction if subjected to static or dynamic loadings. CPB liquefaction would lead to the application of excessive horizontal loads that can lead to barricade failure.

CPB liquefaction is much more complicated that the conventional liquefaction analysis of granular materials such as sand. Hydration and confined environment of a stope are a couple of these complicating factors in addition to the type of input ground motions (i.e., earthquakes vs mining-induced seismic loads). To be able to establish a design procedure, CPB liquefaction analysis must be done first using the conventional geotechnical earthquake engineering concepts. The current state of practice assumes that once the unconfined compressive strength of CPB reaches 100 kPa, the material is non-liquefiable (Clough et al. 1989).

In this paper, first a time domain ground response analysis is performed using FLAC3D. The time dependent material properties due to binder hydration are incorporated into the analysis. FLAC3D results are then compared with the one dimensional equivalent linear analysis results using SHAKE2000. The induced shear stresses are then compared with the laboratory obtained cyclic shear resistances to identify the regions of backfilled CPB that are prone to liquefaction.

Paste backfill reticulation systems are often designed around steady state friction losses and pressure effects from elevation changes. Most positive displacement pumps do not operate at steady state. The pressure pulse, which results from each pump stroke, is a combination of acceleration forces and friction losses. This paper investigates the magnitude of the acceleration forces, explores the circumstances where these forces could become a fatal design flaw, and possible alternatives which reduce or remove the pulses.

In cooperation with the Hecla Mining Company, NIOSH researchers have developed effective methods for monitoring the in situ performance of cemented paste backfill during underhand cut-and-fill mining more than 1,950 m (6,400 ft) beneath the ground surface. Robust and reliable instruments were installed at eight locations in two production stopes prior to backfilling, and monitored over a two-year period through five undercut advances. Horizontal pressures up to 5.50 MPa (798 psi) were measured in the paste fill along with 51 cm (20 in) of stope closure. From the instrument data, the in situ stress versus strain behavior of the paste fill was analyzed, providing an average in situ modulus of deformation of about 3.62 GPa (525 ksi) for the backfill during initial undercut mining. The initial elastic response of the paste fill was typically followed by strain softening and plastic deformation with additional closure. The onset of strain hardening behavior in the paste fill was measured during mining of a fifth undercut advance. The instruments are currently being monitored every two hours by data acquisition systems that are linked through the mine's communications systems to a corporate web site—thus providing the mine staff and NIOSH researchers with reliable, timely information about the backfill's behavior and stability.

For the reason that Anhui Shapinggou Molybdenum mine with large-scale deep mining appears obvious underground pressure, the arch facade sequence mining and subsequent backfilling are designed for controlling the frequent underground movement. The numerical analyses of arch facade mining sequence and conventional upward horizontal slice mining sequence are carried out respectively, and static calculation and dynamic calculation are carried out for the stability of backfill. The analytical results show that the maximum principal stress distribution is uniform in the arch facade mining, and the arch facade mining has smaller degree of stress concentration and less plastic area than those of conventional sequence mining. Because of a better supporting role arising from the vaulting, the surface subsidence displacement caused by arch facade mining is smaller than that caused by conventional sequence mining. The operating range of blasting vibration influences the variation of plastic zone and displacement for backfill. When the blasting dynamic loading is applied near the backfill, the distribution area of backfill plastic zone is expanded obviously. If the curing time of backfill is insufficient, the backfill is prone to collapse.

Cemented rock fill (CRF) commonly referred to as backfill has been utilized as the main support in the underhand cut and fill (UCAF) mining method at the Turquoise Ridge Mine (TRJV). The design is based on flexural instability utilizing fixed beam analysis, originally developed by Mitchell and Roettner (1989) and later Stone (1993). The methodology has been utilized to increase our average undercut width from 20 to 30 feet. The opportunity also exists to lower mine costs by adjusting the cement content without jeopardizing necessary mine design safety factors. Numerical modeling and instrumentation has also substantiated minimal pressures and movement from current designs, and could facilitate even wider undercut widths or expanded mining methods in the future.

The largest operating cost associated with most cemented mine backfill systems is binder. Binder dosage is typically based on the results of the quality control strength testing, a suitable model for estimating the strength requirements and a Factor of Safety (FoS). In the author's experience, safety factors (or equivalent) can range from 1.2 to 2.0, often with no rational basis for selection. At typical mine backfill operations this range may equate to a 1-3M USD difference in annual binder costs. Consequently, selection of a suitable FoS, which properly reflects the material and model uncertainty, is considered necessary.

This paper presents the results of analysis that was undertaken for the purpose of providing guidance relating to a suitable FoS for cemented mine backfill design. Work presented in this paper utilizes Monte Carlo simulations of a typical mine backfill vertical exposure to derive a rational approach for using variable quality control strength data (either plant sampling or in situ measurements) for the design of fill exposures.

In addition to providing a rational approach to addressing material uncertainty, this paper also provides recommendations relating to the selection of appropriate model uncertainty safety factors. While limited in scope the presented results provide useful guidance for the selection of appropriate model uncertainty safety factors when applying simplified analytical solutions, compared with more rigorous numerical methods.

The pore water pressure (PWP) has a significant effect on effective stress and strength development in cemented paste backfill (CPB) structures. Moreover, the PWP has a considerable impact on stability and design of barricades. Hence, it has paramount and practical importance for stability analysis as well as the cost-effective design of CPB structures and barricades. In this study, a multiphysics model is developed and successfully validated against laboratory and field data to assess and predict the development and evolution of PWP within CPB mass. A series of engineering issues are then examined with the model to investigate the PWP in field CPB mass with respect to the changes in the mixture recipe, as well as the backfilling, surrounding rock and curing conditions. The obtained results provide in-depth insight into the PWP evolution in CPB.

Paste backfill and uncemented rockfill are used at the Éléonore gold mine to allow pillarless recovery of the narrow gold veins. A major constraint of the Éléonore operation is to store the sulphide tailings underground. Maximizing uncemented rockfill underground is an important economic factor. A good balance of paste backfill and uncemented rockfill is critical to allow the mill to discharge the sulphide material without compromising paste quality and the continuous mill operation.

This study is part of an ongoing internal research program that aims to find an economical mix design with desired fresh and hardened properties at high sulphide content. The effects of the different mix parameters were evaluated independently using the compressive strength at different curing times. All of the mixes were batched at the same consistency. This paper covers the mix design philosophies and challenges encountered during full-scale implementation tests along with innovative techniques used at the Éléonore paste backfill plant.

Cemented paste backfill (CPB) with excellent flow ability and a high rate of early strength gain achieved in an economical manner is a key target in the backfill technology. This paper presents the results of an experimental investigation of the effect of a novel chemical admixture (Master Glenium 7500) on the rheological properties (yield stress, viscosity) and mechanical properties of CPB. The yield stress and viscosity of CPB samples containing 0%, 0.05%, 0.125% and 0.25% admixture were tested up to 4 hours. Unconfined compressive strength (UCS) of the samples was also determined after 1, 3, 7 and 28 days. The results obtained show that the admixture significantly reduces the viscosity and the yield stress of CPB. The admixture also proved to be important for strength development. At the initial stage, up to 3 days curing period, samples with admixture show lower UCS but become stronger than the treated samples after 7 days. This shows that this admixture can significantly improve the rheological properties, strength and strength gain rate of CPB. The findings of this study will, therefore, help to prepare CPB with enhanced performance properties.

This paper discusses the paste design and the experimental results of using an environmentally benign additive known as engineering backfill fiber (EBF), which can potentially and significantly reduce of the cost of paste backfill. It was found that paste with EBF produced less bleed water and developed higher strength. The improved high early strength allowed a more flexible mining and backfill schedule. EBF may also be used for managing the risk of liquefaction and improve safety. The tailings, binder, and water used in this series of experiments were collected in a real world mining process.

The results discussed in this paper highlighted a Feasibility study of overburden material (OBM) from mines as stowing/backfill material. The study refers significant physical parameters like particle size, dry density, porosity, permeability etc. The flow characteristic i.e. pressure gradient change for slurry transport of OBM for 37.5 mm circular pipe have been experimentally evaluated. The linear expressions related with change in pressure gradient have been presented using multiple regressions of data. Water percolation characteristic after placement of slurry also have been evaluated experimentally. The commonly used stowing material; sand is taken for the comparative analysis with overburden material.

With the development of information technology, digital mines has become a development goal of the mining enterprises in recent years. The equipment intelligent, automation production, management information mining mode of production is being extended gradually, the digital management system of filling has become an important project of digital mined development. This paper studies the remote automatic filling process control, material concentration and flow rate of the real-time monitoring technology, to develop a suitable metal mines filled automatic control system. The system is applied in a copper mine enterprises. The test results show that the system realizes the production equipment and process for remote status monitoring and management, optimize the number of staff, reduce labor intensity and improve packing efficiency, to achieve a continuous and stable mine production.

In order to meet the need of efficient backfills in some low grade and hard-to-recover mines, a new backfilling method named short-processing tailing-storage-free filtration backfilling method was invented by studying on the quantity and concentration control of filtrated slurry, as well as optimizing of mine operating flowchart and cyclone clusters. No tailing storage is required for this system; as a result, tailings can be transported to cyclone clusters directly. Generally, the concentration and production rate of the downstream inside the cluster is between 68% to 72% and 69% to 72% respectively. This downstream then flow directly down to the continuous mixers for the mixing with cement, and ultimately, was filled into the voids through underground reticulation systems and boreholes. The installation time for this system has been reduced to 4 months, while the capital investment and operating cost are also reduced by 70% and 20% respectively. The strength of the filling body, with ratio of cement to sand 1:4, can reach up to 3.2Mpa in 28 days. Therefore, this system can be effectively integrated with the overall mining sequence, balance the mineral extraction rate and processing rate safely, hence to improve the profitability of the mine.

The benefits of incorporating chemical admixtures into mine paste fill designs are numerous and cost effective, especially when incorporating metrics such as energy- and cement consumption, reduced dewatering costs, reduced downtime and pipe blockages as well as reduced plant maintenance costs into the equation. The addition of admixtures is a tool to optimize the backfill product in order to have a direct feedback on the backfill quality and numerous operating cost centres. Using admixtures provides the paste fill engineer with a tool to adjust and modify many variables of the paste mix. The following variables can be modified in order to obtain a cost performing backfill paste: enhanced rheological behaviour (better thixotropic profile, improved slump, better pumpeability), reduced water content, reduced cement content or change of cement type, increased solid content, improved compressive strength and improved cure time. An adjustment to any of the mix design variables can result in significant improvements of the paste cost-performance and reduction in overall operational expenses. Test results have proven that the addition of a single admixture at relatively low dosage of 1% to 3% by weight of cement can have powerful effects in modifying the parameters listed above. A prerequisite for good results is a good understanding about the mineralogy and granulometry of the ore host and therefore the source of the tailing material which leads to a customized adjustment of the used admixture in any given paste backfill operation. This paper outlines results from different mine backfill pastes and how to come up with the right admixture choice.

Wear is the result of material loss due to impingement, impact, scuffing, and the sliding of particles across the material surface. Add to that the many other variables which affect the wear rates such as pressure, temperature, velocity, and particle size just to name a few. With that being said wear is very application specific. There are a few standard tests such as the National Bureau of Standards (NBS), DIN and the Taber Abrasion that provide guidance, but often specific field tests must be conducted to determine the best material. This presentation describes the relationship between lab data and field results with various types of cast polyurethane systems. In the end, experience in various operating environments is often needed in order to select the proper polyurethane system for the specific wear service.

There are many forms of backfill that can be considered for a specific mine application and the mine plan, layout and mining method are all key criteria required to develop the appropriate backfill properties. In some instances, a high strength fill may be required for large bulk open stopes and aggregate fill may be the best solution. However, generating suitable aggregate can present logistical challenges and so is often considered an expensive option, but in cases where development waste is readily available, a cemented aggregate fill (CAF) may be an appropriate and cost effective solution. Open stope mining creates large voids and properly designed backfill is used to ensure regional stability as well as to maximize the extraction ratio. CAF is broadly defined as a rock fill that can be modified to suite the mining requirements by optimizing the particle size distribution through a combination of screening, inclusion of tailings or crushing of the waste rock, and adding binder such as cement. The requirements to conduct UCS test work on CAF presents unique challenges and a specially designed and constructed 50 tonne load frame was developed for this test work. This paper presents results from a series of laboratory scale tests on CAF to determine the effect of particle size distribution on the unconfined compressive strength (UCS) so as to optimize the binder content of a CAF backfill product.

Backfill production can be challenging in a mining environment in which multiple mining methods are in use (longhole, overhand & underhand cut and fill). It becomes even more complex when there are multiple headframes, two processing facilities, and associated pastefilling facilities, and where many small, high grade stopes take priority over all others. The complexity of this type of operation in a mine that is mature and where the stoping areas are widely spaced and deep, can present many obstacles to maintaining the ideal inventory of stopes ready to fill and the reticulation to support.

Numerous associated obstacles over time led to a backlog of 80,000 tons of unfilled stopes. Such a deficit is very difficult to overcome when the pressure to meet targeted ounce production can lead to short term decisions which eventually create long term pain.

This paper describes the actions that were taken to completely overhaul the backfill process, eliminate the backlog and implement a sustainable system that will ensure the future success of the mine.

Through innovative improvements, via a structured team approach, with a focus on design flexibility, improved processes, optimization, and a simple mantra "do every task as soon as you can do it," significant step changes in backfill management were achieved.

Changes to organizational structure, planning, scheduling, and coordination, along with optimized preparation, transportation, and distribution, were achieved through the introduction of a philosophy where through team work, collective awareness, understanding, and ownership successful outcomes are achievable.

Expanding the existing pastefill distribution system to the East Zone of Minera San Rafael's Escobal Mine posed a challenge due to long pumping distances and high discharge elevations. Several options were considered for delivering pastefill to the new area which included procuring a replacement higher pressure surface pump, installing an underground booster pump station and increasing the efficiency of existing site infrastructure with a pressure damper and admixtures. Hydraulic modelling inputs were refined after a series of field trials and the final decision was made to use admixtures and to install a pressure dampener to reduce peak pressure spikes and increase the average operating pressures with existing site infrastructure. This paper outlines the steps taken to reach this decision including testing, modeling and an economic evaluation. It presents how the pressure dampener and admixtures are used to extend pumping distances while maintaining targeted paste quality.

Deeper underground mining is becoming more prevalent throughout the world. With this comes the fact that the installation of infrastructure to deliver bulk materials in support of mining can add significantly to the overall cost of a project. To this end, the multi-purposing of required infrastructure can lead to significant cost savings during a mine's development, and operation. The use of cemented paste backfill dipped boreholes for delivery of concrete and shotcrete underground is one possible way to bring about economical and efficiency benefits to a project. This paper presents some of the design and technical consideration that went into such an evaluation as part of feasibility studies undertaken by Glencore's Sudbury Integrated Nickel Operations (Sudbury INO) for the Onaping Depth (OD) Project.

Minefill is widely used in underground mines around the world, mainly to improve ground stability, reduce ore dilution and maximize ore recovery rate. To successfully apply backfill, it is a critical issue to evaluate the stresses in backfilled stopes. Previous published works have shown that numerical modelling is an effective means to accomplish this task. However, most of the numerical models did not consider interfaces between the backfill and rock walls. The influence of the mechanical properties of the interfaces was seldom systematically investigated on the stresses in backfilled stopes. In this study, the stress distribution in backfilled stopes is analyzed using FLAC3D after taking into account interface elements. The influence of the planar and nonplanar interfaces, as well as the shear strength and roughness on the stresses in backfilled stopes will be presented and discussed.