Publications

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.

Cemented paste backfill (CPB) is increasingly applied in underground mines world-wide and has a broad prospect considering its benefits in environmental protection and ground control. During the paste production, a well-graded aggregate is critical for the achievement of CPB. Mine tailings from the outcome of ore-dressing plant are commonly used as the fill aggregate. However, it is difficult to obtain an ideal particle size distribution for the mine tailings which are roughly mixed with final residuum in ore concentration processes. In this study, a novel industrial method is proposed to select fill aggregates from different parts of ore-dressing processes. With combined design of concentration plant and backfill plant, the tailings with desired particle sizes and proportions during the mineral processing are chosen to produce CPB without disturbing the regular ore concentration. The problem of passively accepting final tailings from ore-dressing plant has been improved.

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.