Publications

Routine sampling and testing of paste mixes with uniaxial compression test cylinders is an accepted industry practice for routine monitoring of paste quality and strengths. However, unlike the concrete industry, there is no industry accepted quality control standard for assessing the results, or for determining what actions, if any, need to be taken. This paper sets out the groundwork for an industry standard for interpretation of routine quality control testing of paste mixes. The paper will examine the variability of several key benchmarks based on mine site quality control databases, and provides a draft assessment criteria.

In 2018, a remediation program was executed to stabilize the underground voids near stopes that store arsenic trioxide waste at the Giant Mine in the Northwest Terri­ tories of Canada. The shapes of the voids were reconstructed through integrating multiple cavity monitoring system surveys. A number of mix recipes of paste backfill and self- consolidating concrete (SCC) were designed with various bleeds, set times, uniaxial compres­ sive strengths, and flow properties. Respectively, a total of 16,686 m3 and 53,389 m3 of SCC and paste were backfilled by gravity.

Eleonore Mine experiences high transient forces in their pastefill underground distribution system which results in significant damage to the pipeline supports. This investi­ gation examines the causes of the transients in this pumped system and looks at their effect. A transient flow model was developed and validated using operating data. The investigation showed that favourable transient conditions came from operation in full flow conditions. It was also shown that a misaligned hydraulic pulsation dampener can produce higher transients in the line than would be experienced without one. This investigation spurred design and oper­ ating strategy changes to combat transients in the underground distribution system.

Historically, strength development in underground backfill is estimated based on the results of historic unconfined compressive strength (UCS) testing. During both prelim­ inary study phases and operational phases are batched to specific solids and binder contents and placed in curing chambers, with the intention that these chambers replicate the curing conditions experienced underground. The rate of strength development in mining backfill can be greatly affected by variations in environmental factors including temperature & humidity. Therefore accurate representation of in situ curing conditions for cemented specimens is crucial. This paper investigates the effect that differing curing conditions can have on the strength development of cemented mine backfill specimens. This paper explores how variations expected to be encountered in typical fill masses impacts the resulting strengths and also inves­ tigates how aspects that may appear subtle can actually have a significant impact on the resulting measured strengths. Given the findings of this investigation a series of recommenda­ tions are provided for improving the way mine backfill curing chambers are managed.

Direct shear tests were carried out with planar interfaces between cemented backfill and rock to obtain cohesion and friction angle. Triaxial compressive tests with the same backfill were used to reveal proportions of shear parameters between interface and back­ fill. Nonplanar interfaces with different roughness were shear tested for further comparison. A constitutive model for interface was modified based on Mohr Coulomb criterion, which could used to investigate interaction between backfill and rock mass. Numerical simulated shear stress strain were used to validate the model.

One of the problems of the mining industry is the management of fine mineral tailings (with a solid phase diameter of less than 0.1 mm),which are the result of the enrich­ ment process. Due to their physical properties, mainly thickening and compressibility, the fine-grained materials are not suitable for use in large quantities in the mining industry or other industrial branches. A number of experiments were conducted to develop a technology allowing the practical use of fine-grained post-flotation tailings as hydraulic or cemented hydraulic fill and also as a material for goaf tightening. The paper presents the results of the research conducted on obtaining condensed fine-grained tailings of copper ore flotation by the dredging method. During the experiments, the following parameters were determined: pump operation parameters, material density, linear head losses On top of this, the process of depositing material on the beach was assessed. During the research both traditional measure­ ment methods and laser scanning techniques were used to assess the deposition of material on the beach. Experimental studies have confirmed the effectiveness of obtaining material by the dredging method that can be used in backfilling technologies or for goaf tightening.

Backfilling and filling voids in Polish underground mines has mainly two faces: the classic hydraulic backfilling and caulking gobs with use fine-grained mixtures. The first type is backfilling, in which the main material is sand has over 100 years of tradition in Poland, but in recent years it has virtually disappeared in hard coal mines. There are used for almost 30 years other methods - caulking and filling voids caving mainly with mixtures based on different types of fly ash. Fine-grained hard coal waste is eagerly added to such mixtures, which is the cheapest way to manage it. In recent years there have been a number of changes on the ash market. Their price increased significantly due to widespread use in the construc­ tion sector. Coal mines wanting to use known and proven technology at a low level of costs, are forced to look for alternative mixtures, based more on their own waste. The article describes the properties of caulking mixtures based on own (mining) waste with the addition of parameters improving the parameters. The possibility of producing binder mixtures with higher mechanical properties was also assessed. The scope of research concerned the proper­ ties of mixtures in a liquid state, including rheological properties, as well as the properties of mixtures after hardening.

A popular method to determine backfill strength for sidewall exposure assumes that the cohesive bond strength is equal to one-half the Unconfined Compressive Strength (cb = ½ UCS). A new laboratory study uses direct shear, UCS, and novel ten­ sile strength test results to show that this strength assumption is not valid for the tested CPB (and quite possibly many other CPBs). The implications of this finding in the con­ text of strength for exposed backfill sidewalls is investigated using generalized design examples.

CPB pressures up to 3.3 MPa have been measured arising from rock closure on the backfill. However, backfill has never been tested at pressures this high and therefore its response to high stress needs investigating. A high-pressure compression test device is described. Test results are presented for isotropic compression tests up to 6.5 MPa. The key parameters defining compression response are related to quality UCS test results. The general behaviour is very stable and extrapolating the results to several times the pressures used seems feasible, indicating CPB’s suitability for deep and high stress mining.

Currently there appears to be no rational method of defining plug strength in a typical “plug and cure” backfilling strategy, which is a significant problem when many engineered backfill containment structures include assumptions that the backfill plug isolates the structure from pressure applied by the subsequent “main” backfill volume. The proposed method for plug strength determination is presented as an analytical solution supported by numerical modelling and case study data. By extension, this method enables definition of required backfill strength for continuous backfilling.

In the mining industry both segregation and thickening of flotation tailings are usually used to obtain backfill material. The use of flocculants in the process of thickening tailings causes a change in the rheological parameters of the obtained mixture which directly affects the flow conditions and segregation of the solid phase. The paper presents the results of semi-technical tests of thickening, deposition and segregation of the copper ore flotation tailings. Thickening tests with and without flocculants were carried out. The material obtained at the underflow was deposited in prepared measuring ditches. During the experiments were monitored such parameters as the flow rate, particle size distribution of the solid phase and the density of the feed, overflow and underflow. The results of the experiment were analyzed with regard to the use of the underflow stream as a backfill material. After exceeding critical concentration of the solid phase, the movement of non-Newtonian fluid was observed in measuring ditches whose role was to simulate the spread of backfill in the post-mining void.

South African gold and platinum mines commonly utilise narrow tabular mining for ore extraction. The removal of the ore body leaves open voids with stoping widths that can exceed 2 m in some mines. Props and cementitious grout packs are used extensively as stope support systems to stabilize the rock mass of the voids and to reduce the risks associated with rockfalls and rockbursts. The construction of grout packs for support follows the stope face advance and mining production is inter alia dependant on the production profile of the grout packs. The grout pack production system of a mine generally consists of a surface mixing plant and a reticulation system to the underground workings. A cementitious grout slurry is prepared at the mixing plant and is pumped to the underground stopes for filling of grout packs positioned between the hanging wall and footwall. Construction of grout packs in stopes is labour intensive and requires plan­ ning to ensure that the grout pack production profile meets the mining production pro­ file. To determine the planned monthly grout volumes of a mining operation a variety of parameters need to be considered. These parameters should be accurately estimated at the start of a production month and are based inter alia on historical data and the mining plan of the operation. This paper presents a method to assist mining staff in esti­ mating the required grout pack production profile, determining the required capacity of grout plants and reconciliation of the actual and planned grout pack production profile for a production month.

Paste backfill technology has become increasingly relevant to the mining industry, providing not only a safe way for the underground disposal of tailings but also essential advantages for ground stabilization and optimized ore recovery. Yield stress is among the most important rheological properties of paste backfill, which determines its trans­ portability during long distances. Measurement of yield stress is a challenging and complex task, given the high number of variable factors. So far, no standard procedures and methods have been established for measuring the rheological properties of paste backfill, in particular yield stress. This experimental work consists of the development of an accurate laboratory testing pro- gramme that will allow for the evaluation, measurement and understanding of rheological yield stress of paste fill. For this study, tailings from Zinkgruvan (Sweden) and Neves-Corvo (Portugal) mines were analysed. A series of laboratorial tests were conducted including the following test procedures: slump, flow table spread, fall cone and the vane technique (applied using a viscometer and a rheometer). The correlations between the yield stress, measured by vane technique and other test methods, were obtained from the test results. Additionally, preliminary conclusions were drawn regarding the influence of physical properties of tailings (particle size distribution, dry content, uniformity coefficient and coefficient of gradation) on yield stress by a statistical study using multiple linear regression models. The fall cone test has resulted in the best correlation measurement of dry content and of yield stress measurements using the viscometer and rheometer. Being a simple, inexpensive, and expedited method for paste yield stress measurements, it is considered effective for quality control and/or rapid on-site measurements of paste fill.

Traditional manual approaches to managing backfill systems are being replaced with improved and more efficient methods that are faster and safer. Automated diverter valves are among the technologies being used to effect efficiency and safety gains. Using diverter valves eliminates time-consuming manual operations that require special equip­ ment and put workers in harm’s way. A case study that assesses automated diverter valve operation and manual diversion at an Australian mine provides a comparison of functionality, time-savings, and safety advantages inherent to the diverter valve.

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.

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.