?To explore the spatial strength distribution of backfill in the stope, a group of experiments in a large similar stope model was designed for simulating the consolidation of cemented tailings backfill (CTB) in a stope. The height of CTB in similar stope model was measured to analyse the flow and sedimentation characteristics. The unconfined compressive strength (UCS) test on specimens cored in the different position of CTB sample in similar stope model was conducted. Moreover, the particle size and cement content of CTB sample were tested to help to explain the mechanism. The results show that during the flow and sedimentation of filling slurry in the model, inconsistency of the particle size and cement content leads to the inconsistency of strength. In the flow direction (horizontal direction), the median particle size of CTB first increases and then decreases, the cement content of CTB decreases slowly and then increases sharply, and the strength of CTB first decreases and then rises. In the sedimentation direction (vertical direction), the cement content of CTB decreases with the increase of depth, while the strength of CTB increases with the increase of depth. The strength is affected by the interaction between particle size and cement content, and the higher cement content of CTB does not translate into higher strength. The results provide a theoretical basis for improving the quality of CTB and optimizing the design.
This report identifys and recommends a standard method for measuring the in situ undrained shear strength (or appropriate equivalent measurement methods) for all tailings deposit types that are technically and statistically appropriate for AER reporting.
Olympias Mine is operated by Hellas Gold S.A., a subsidiary of Eldorado Gold Corporation. The orebody shape and size are suitable for a drift and fill mining method. The mining sequence is overhand and the demand for backfill strengths are generally low except for the initial sill cuts. The design fill strengths are determined from the planned stope exposures to allow for safe extraction of the ore in adjacent drifts and immediately below the initial sill drifts with minimum dilution. Due to the permit constraints imposed on mining at Olympias Mine, after an environmental impact assessment, there is a requirement that the final backfill strength must reach a uniaxial compressive strength (UCS) of 4.0 MPa at 28-day cure age. By developing a suit of mix recipes incorporating superplasticiser admixtures, it was possible to achieve the strength demands and the workability of the backfill. This paper presents the results from comprehensive test work conducted on whole mill tailings and cyclone mill tailings to produce high strength backfill.
While not specific to tailings, this webinar includes valuable knowledge for tailings engineers. This webinar series discusses and presents fundamental and advanced topics for engineering with GCLs, with emphasis on waste containment applications. This webinar presents fundamental and advanced topics for static internal and interface shear strength of GCLs for stability analyses.
While not specific to tailings, this webinar includes valuable knowledge for tailings engineers. For proper utilization of PVDs (also called wick drains) in of saturated fine-grained foundation soils, one must understand their installation, requisite theory, remaining issues and the opportunity of strengthening (not only dewatering) the soil mass. This webinar provides this specific knowledge.
Mavres Petres mine is an underground mine, located in Chalkidiki, northern Greece, that is owned and operated by Hellas Gold; a wholly owned subsidiary of Eldorado Gold Corporation. The mine extracts a highgrade lead and zinc orebody using drift and fill mining method. Backfill is an integral part of mining cycle at Mavres Petres mine. Filtered coarse tailings mixed with cement are used for making cemented hydraulic backfill in a surface batching plant. The paper will discuss and present an overview of the backfill optimisation efforts at Mavres Petres mine, which includes recent changes and upgrades in the backfill plant, improved mix design, backfill quality control, and backfill delivery and placement in order to improve the operational efficiency, product consistency, safety and economic viability of the mine.
Cemented paste backfill is an increasingly popular technique to improve ground stability in underground mines. This technique is used in several mining methods that require strength evaluation for the vertically exposed cemented backfill following the excavation of an adjacent stope on one side. The critical strength is generally evaluated with an analytical solution proposed by Mitchell et al. (1982). Despite its wide acceptance in academia and application in the mining industry, the Mitchell solution has received only a few updates in the literature, including some new developments given by the authors and colleagues. The original Mitchell solution and its variants were mainly validated against the physical model test results obtained by Mitchell et al. (1982). Even though the Mitchell model debatably assumed a zero backfill friction angle, the required strengths predicted by the Mitchell solution corresponded quite well to those obtained by physical model tests. This study reanalysed the Mitchell solution and its physical model. The testing conditions and procedures for measuring the shear strength parameters are investigated. The stability of the cemented backfill upon removal of a confining wall is analysed with FLAC3D. The comparisons between the numerical modellings, experimental results and analytical solutions are presented, and the applicable range of the classical Mitchell solution is discussed. A new analytical solution is proposed to evaluate the minimum required strength of the cemented backfill confined by two sidewalls exposed on one side and subject to pressure from uncemented backfill on the opposite side. The proposed analytical solution is validated by numerical simulations with FLAC3D. The proposed analytical solution is used to determine the theoretical strength requirement of cemented backfill in primary stopes of an iron mine that employs stage stoping with subsequent backfill mining. The floating Factor of Safety (FS) characterising the current backfilling quality control level of this mine was statistically evaluated with a large amount of uniaxial compressive strength (UCS) data after testing vast drilled samples from field stopes. The engineered strength requirement of the cemented backfill in primary stopes had been finalised by combining the analytical results and floating FS of the mine.
Thin spray-on liners (TSLs) provide areal support to rock excavation surfaces, and have been implemented in the mining sector for over 20 years. However, scepticism over their usage still prevails, despite the results of laboratory research that has been carried out indicating their effectiveness for use in mines. The study described in this paper aims to highlight TSL performance as viewed by the mining industry. Some underground cases of practical performance have been singled out and compared with the expected performance based on information from suppliers and from laboratory testing perspectives, and the causes of the resulting quality of performances were categorised. Among the causes of the discrepancies between expectations and observations is the lack of inclusion of parameters such as temperature and humidity in the laboratory tests, which could have significant effects on the liner performance since, based on results from Brazilian indirect tensile tests on coated samples, their inclusion doubles the probability of failure and therefore, increases the predicted geotechnical risk of failure. Consequently, to take into account potential performance discrepancies, some existing recommendations and further potential recommendations are suggested in the paper. If later validated, these suggestions could be included in a good practice guideline for TSL application in underground mines.
The overall objective of thickened and paste tailings disposal has been stated many times: it is to thicken a tailings slurry to the point where it is non-segregating, and will beach to form a sloping, sub-aerial deposit. The advantages of this type of scheme have been stated to include higher density, higher strength (including avoidance of a slimes pond), improved seismic resistance, and better closure and rehabilitation prospects (including lower compressibility). The aim of this paper is to show how these outcomes are a product of the interaction of fundamental tailings properties, site management practices, and climatic conditions of the site. A typical set of test results is presented and discussed in the context of unsaturated soil mechanics. The absence of segregation in thickened and paste tailings is an important factor, but it is often overlooked. The paper addresses the influence of evaporative drying on the sub-aerial beach. The induced suction stresses, combined with compressibility (consolidation) largely influence the rate and extent of density and strength gain that is attributable to the thickened discharge method. Finally, the influence of overall site management practices (e.g. filling rate), together with climatic conditions, are discussed to illustrate how these may act as constraints on the potential to achieve optimum results.
The long-term strength of cemented backfill mass with ordinary Portland cement binder generally decreases with sulphide content due to the formation of expansive phases such as gypsum. This paper investigates the potential of using commercial reactive MgO-activated ground granulated blast furnace slag (MgO-GGBS) in cemented backfill from high sulphide content lead-zinc mine tailings to prevent long-term strength loss. The study focuses on the effect of MgO-GGBS content and the reactive MgO dosage on the unconfined compressive strength (UCS) and the shrinkage/expansion rate. The test results showed that the 28-day UCS of cemented backfill achieved the target strength (?1.0 MPa) with 14 wt% MgO-GGBS content, and the reactive MgO dosage affected the long-term UCS and the shrinkage/expansion rate of cemented backfill body. The main hydration products when using MgO-GGBS were hydrated calcium/magnesium silicate (C-S-H/M-S-H) and hydrotalcite-like phases (Ht). Cemented backfill has a porous opening microstructure. Micro-expansion produced by appropriate MgO content can increase microstructure density, which increases short- and longterm UCS of cemented backfill body, while sustained expansion produced by excessive MgO could destroy the MgO-GGBS microstructure, decreasing the UCS of cemented backfill. We conclude that the mechanical and extension properties of cemented backfill body are highly dependent on the reactive MgO content of the MgO-GGBS. The optimum value of responsive MgO content of MgO-GGBS was 2.57.5 wt% to achieve the long-term stability of cemented backfill.