Publications

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.

George Fisher Mine (GFM) is currently in the process of optimizing its backfilling placement and backfill barricade designs. Part of this process involves the installation of in situ and barricade instrumentation to monitor the loads being placed on the barricade and the response of the barricade to these loads. This paper presents the first installation at GFM, which involved total earth pressure cells and piezometers installed immediately upstream of the CPB barricade wall, and ShapeAccelArray instruments installed on the downstream side of the barricade. The results obtained showed that the pressures experienced by the barricade were lower than anticipated and significantly lower than GFM's current barricade design stress. The isotropic stress period (i.e. the backfill's fluid state) of approximately 5 hours was also shorter than expected. The instrumentation also measured some periods in which pressures increased even through the paste plant was not in operation. There also appears to be a positive correlation between pressure and temperature may indicate thermal expansion. Overall, this test is a first step in helping characterize GFM's in situ backfill behavior, providing encouragement that efficiencies can be found within the backfilling system. Further tests featuring more comprehensive installations are in preparation.

In the 10 years since Grabinsky and Bawden (2007) published initial data from an extensive campaign of in situ measurements of backfilling stopes, a better understanding of how in situ backfill behaves, and how operations can use this information to safely improve the efficiency of their backfilling operation has developed. In part, this is due to an ever increasing catalog of published field data. In order to continue this trend, we present a detailed review of the instrumentation, and installation techniques that have worked best as the initially research focused work has been applied on a consulting basis. A recent case study from Barrick Gold Corporation's Williams mine is presented, where relatively low (63 kPa) barricade pressures were measured during a trial to investigate the suitability of continuously backfilling. Importantly, the transition from hydrostatic loading occurred within several hours, which indicates the transition from a fluid backfill to soil-like material was relatively rapid, and likely is a key factor in the relatively low barricade pressures. This data indicates that subject to appropriate QA/QC, including real-time monitoring of barricade pressures, reduced stope cycle times through more efficient backfilling may be possible. Further, barricade displacement has been measured and demonstrated to correlate with barricade pressures. The peak displacement was 0.4 mm. This data will be useful in a site specific barricade strength calibration project.

The Garpenberg Mine in Sweden is owned and operated by Boliden, producing lead and zinc concentrate. The mine has been operated by Boliden since 1953, and has recently (2014) undertaken a major operational and production upgrade with the construction of a new processing plant operating at 2.5 Mtpa of ore production. The revitalisation being driven primarily by the discovery of increased mineral reserves and resources offering a production life past 2030.

A backfill system has been operating at the mine since 2007, producing a paste backfill from de-slimed mill tailings. Between 2015 and 2016 Boliden, with support from Paterson & Cooke's Backfill Group undertook a program of work to improve the operational performance of the system, focusing on increasing system availability and throughput, as well as enabling reticulation into the new Kvanberget ore body.

This paper is presented as a case study to describe an approach to overcome commonly encountered paste reticulation system problems, notably expansion to new mining areas, system availability and excessive system wear. Specifically, the case study describes how, through the introduction of diversion valving, level loops and hydraulic modelling, the system availability has been increased. The hydraulic modelling including completion of a rheological loop testing to better quantify the paste characteristics so that, through hydraulic modelling the consistency of the backfill could be adapted to ensure full flow operating conditions, accounting for inclusion of the new level loops.

As development projects and operating mines drive for efficiencies, both capital and operating cost are often scrutinized. The selection of technically viable and cost effective backfill is an important task for many underground mines. This paper presents the findings of a study for the Twin Metals Minnesota Project that looked at the results of combining a tailings that readily dewaters, with a slow set binder, such as slag cement. The resulting proposed backfill plant design takes on the simplicity reminiscent of a standard hydraulic fill plant yet maintains the performance and operational benefits of a typical paste fill plant. In this case, dewatered tailings from a high rate thickener can be combined with slag cement to achieve unconfined compressive strengths that are similar to paste.

There are a large number of different sizes and shapes cavities when mines use the openstope method to mine, and these cavities will have influence on mine condition, then cause serious geological hazard such as the roof fall, rib spalling, closure deformation of the cavity, even surface collapsing, all of geological hazard can threaten mine safety. Using backfill method to deal with dangerous cavities is the best efficient method which will prevent wholesale ground pressure activity. However, it is difficult to obtain cavity shape and calculate backfill amount if mine uses backfill method to deal with dangerous cavities. To solve this problem, this paper introduces the 3D laser scanner for mine which is developed by Beijing General Research Institute of Mining and Metallurgy to scan cavity before mine backfill and probe the whole or part shape and real time condition of cavities, then obtain whole, comprehensive, continuous point cloud data. point cloud data will be converted into line model, entity model, profile data, these data will provide intuitive information to constitute backfill process for cavity and calculate backfill amount precisely to solve the problem which is difficult to check backfill amount of cavity.

Salt mining in Austria commences today for more than 5000 years. Past mining activities have left remnant stopes which could pose a risk for mine stability. A research project was initiated to develop a backfill design methodology for the special conditions encountered in the salt mines. Special focus was laid on the determination of suitable rock mass parameters since the host rock exhibits a time-dependent behaviour. It was possible to establish parameters for the rock mass and the backfill using a large 3D-model comprising the complex mine geometry, high precision levelling measurement data and stress measurement data. The filling of these remnant stopes was completed without incidents based on the findings of the presented study.

Polish underground coal mines successfully adopt new method of filling of gob area in logwall. Currently, due to cost reasons, most of conventional backfill operations have been stopped, however many mines are equipped with the hydraulic backfill infrastructure. This infrastructure, mainly pipelines networks, can be easily applied for transportation of fine-grained mixtures used for filling of gobs. Placement of ashes, slag and processing waste in mined areas at Silesian coal mines began in XIX centuries. Such practices have been employed at both active and abandoned coal mines. The current filling technology of gob area in longwall operation allows to avoid surface subsidence, utilize fine waste and saline mine waters, improve stability of rock mass and reduce some of the ventilation problems such as loss of air into the gob in the headgate area (the loss can reduce the air available to ventilate the longwall face), gas emission and spontaneous coal combustion. The purpose of this paper is to present the current fill operation, the results obtained by applying a new method in longwall mining and a number of problems related to environmental and safety issues. Physical properties and requirements for fill materials and mixtures will be discussed.

The Northam Platinum Zondereinde mine is performing multi-reef mining by exploiting two types of platinum bearing reef, known as the Merensky and UG2 reefs, each with differing ore characteristics and resulting tailings properties. The mine has been using uncemented hydraulic backfill for primary as well as regional support since the start of the mining operations in 1993. Historically, the backfill material comprised of classified Merensky and, to a lesser extent, development waste tailings. Northam Platinum Zondereinde mine is now investigating the use of UG2 tailings as backfill material should the availability of Merensky tailings not meet the required future volumetric placement demands.

The suitability of UG2 tailings as backfill material was investigated through benchtop tests, followed by a full-scale test paddock on surface. The test paddock was equipped with total earth pressure cells and piezometers to assess the stress build up in the backfill during and after placement as well as the drainage potential of the material in the paddock. In addition, different geotextiles were trialled to optimise the volume of drainage water, while limiting the amount of solids released from the trial paddock.

During the field trials, slumping events were witnessed inside the test paddock which resulted in increased loading conditions on the fill fence. This paper presents the backfill system, test setup and results from the field trials as well as a discussion, and probable causes, of the slumping events that were witnessed during the field trials.

Many mines start as an open pit operation and advance into underground developments. In some cases, paste is selected as the backfill method of choice. For these operations the potential to place tailings in the existing inactive open pit can be beneficial from an environmental and cost perspective. The operation can delay or eliminate the need to permit a new tailings storage facility. One of the key challenges with in-pit deposition in general is the management of water. A highly dewatered tailings such as paste can be the solution, and to those operations that have a paste backfill plant, the advantages are apparent. This paper discusses the engineering considerations for an in-pit tailings disposal design with a particular focus on the advantages of delivering a paste consistency material.

The safety science is trapped in the management concept that 'what gets measured gets done', and the belief that incidents rates are actually validly and reliably measuring safety performance. We give incentives based on false data, and we spend huge resources on misconceptions, achieving little more than looking very busy.

The more recent focus on the art of leadership, as against the 'science of management', has brought a deep and different understanding of people in the work place - that human motivation is a complex but powerful force that can be harnessed. The approach argues that if people are given authority and trust, they will excel. If people understand and believe in the true purpose of safety, they will sign up.

When it comes to promoting job-site safety, how much messaging is too much? How much risk-identification and management is too much? Is there such a thing as too many safety rules and guidelines? While most people argue that job-site safety can never be promoted enough, one safety-industry researcher suggests otherwise.

Corrie Pitzer argues that many organizations suffer from delusions when they think about safety. He suggests that by driving risk-identification and risk-management strategies, as well as promoting "unrealistic" goals such as zero accidents, safety managers unwittingly create organization-wide delusions that actually cause more harm than good.

Because Pitzer uses strong language to describe his approach, he's often characterized as not caring about ordinary men and women who risk injury or death in dangerous workplace situations. Nothing could be further from the truth. Rather, Pitzer and his team study traditional approaches to safety through unusual means, and the conclusions they draw are based on data gathered through years of careful study.

Analysis shows, quite clearly, that some of the modern approaches to workplace safety have fostered more harm than good. Although the approaches themselves are not without merit—it's reasonable to want to control risk, and it's laudable to want to reduce accident rates—as a society, we have arrived at a point where organizations drive such approaches harder than ever, to the point where these notions are being followed slavishly and without any regard to their broader consequences. According to the author, accidents are largely not preventable. As organizations are operating increasingly closer to 'zero', accidents are increasingly random events, caused by chance circumstances and inherent risks that randomly interact. Moreover, by creating illusions of compliance and consistency, where workers are encouraged to follow rules and procedures unquestioningly and without relying on their own common sense and instincts, safety systems can actually promote disaster.

The author describes seven deadly delusions from which organizations suffer.

There are many ways to design and construct a backfill plant for cemented hydraulic fill (CHF), cemented rock or aggregate fill (CRF/CAF) or cemented paste fill (CPF). Backfill plants can be simple, mobile plants that require little in the way of permanent fixed infrastructure. Prefabricated modular plants are also an option and can allow clients to reduce construction costs by performing the majority of the construction and assembly work in a fabrication shop rather than on site. Lastly, custom plants, constructed at the minesite can be designed around competitively-bid equipment, with the optimum layout for operation and maintenance without any limitations due to transportation size restrictions or equipment dimensions.

The three backfill plant options listed previously (mobile, modular and custom), and a variety of hybrid options that mix the characteristics of the three, are not always well understood and the risks, advantages and disadvantages of the various options can be overlooked when selecting a plant option that is right for a particular site. This paper seeks to identify the various options available for backfill plant design and discusses the pros and cons of the options. The intent is that this paper will help mine operators understand their options better, match their approach with their environment, and avoid unintended consequences when selecting a backfill plant type.

In China's western eco-environment frangible area, the traditional fully mechanized caving or room mining method is facing coal pillar instability, mine earthquake, large-area roof subsidence in the goaf, surface subsidence, water and soil loss, vegetation deterioration and other environmental problems. To solve the aforementioned problems and improve coal recovery, the roadway backfill coal mining (RBCM) technology with water-preserved was proposed as a solution and its technical principle, key equipment, roadway layout and backfill mining process were presented in detail in this paper. The mechanical properties of backfilling materials with different ratio of aeolian sand, fly ash and cement are studied in laboratory for a optimum ratio for local coal mines. moreover, a two-dimensional physical simulation model is established to analyze the characteristics of overlying strata movement and effect of water-preserved. Field application results shows that this technology can effectively control the overlying strata movement and improve the recovery rate of coal resources, achieving the coordinated development of the western mining area resources exploitation and environmental protection purposes.

The treatment of tailings and paste from ore processing filtration and dewatering has gained more and more significance in the recent years. The recovery of water from the process is an important target with respect to both economic and environmental aspects because water is a valuable resource. The dewatering of tailings allows dry-stacking which is environmentally more acceptable, safer, and cheaper and especially with mine backfill it allows to reduce the amount of cement to be added which may save millions of dollars per year.

The most common dewatering technologies for the filtration of tailings and paste from ore processing are filter presses, belt filters and rotary vacuum disc filters. Among these the vacuum disc filter is the most economical technology in most applications - both in CAPEX and OPEX – especially, when high performance disc filters of modern filter design are used. The Boozer disc filter is a modern high performance vacuum disc filter which has set the pattern in a multitude of applications. In the recent years this filter type has established itself in many applications of tailings dewatering initiated by a first reference application which started operation in 2010. In this application the use of two Boozer disc filters allowed to reduce the input of cement by about 60 %.

The reasons for the successful operation of this disc filter in tailings dewatering are: the high throughput and dewatering performance, the excellent operational reliability even in case of varying feed conditions, the simple and robust design, the ease of maintenance and last but not least the small footprint.

The paper reports on operation experience and operation results of tailings dewatering with the Boozer disc filter from 3 different plants with 3 different tailings. In one of these plants a Boozer disc filter is operated in the Andes in more than 4000 meter above sea level.

The mining industry has recognized the advantages of high density backfill or 'paste', which is typically pumped with a hydraulically driven piston pump. Due to the discontinuous flow of this type of pump, pressure pulsations can occur in the discharge line. Pressure pulsations are an undesired phenomenon in pumping installations for a number of reasons, such as damage to the pumping system, including piping and supports, disturbing noise levels and even safety risks for operators and maintenance personnel. This paper describes an advanced system on the GEHO® piston pumps, which will prevent pulsations from occurring, rather than merely reducing the already existing pulsations.

A prefeasibility-level mine closure study of the Metates open pit, gold and silver project in Mexico was recently completed that involved optimized partial backfill of tailings into the pit. The study considered several treatment options to improve pit lake water quality including mixing of lime with the upper horizons of tailings backfill in order to neutralize acidity in the tailings pore water and pit lake. Models of groundwater flow, water balance and pit lake geochemistry were used to predict and optimize the pit lake water quality. Results highlighted trade-offs between the treatment options and were used to manage the overall project cost and risk.

Underground mines use intricate piping networks, known as paste backfill systems to fill stopes after extracting materials for processing. These piping networks require extensive manual labor to operate and maintain a functional system, as these systems operate under extremely rigorous conditions. Diverting paste fill from one stope to another requires removal and reinstallation of the pipe to redirect the flow of the line. This process is laborious, time consuming, and requires extensive planning to ensure safer operations. New innovations and products are now making these manual processes a thing of the past, resulting in increased backfill reticulation, job site efficiency, and safety. This paper evaluates a new system that uses a diverter valve, as opposed to manual changeover, to reduce downtime, eliminate safety hazards, and increase processing throughput.