Special Issue "Backfilling Materials for Underground Mining"

A special issue of Minerals (ISSN 2075-163X).

Deadline for manuscript submissions: closed (31 January 2019)

Special Issue Editors

Guest Editor
Dr. Abbas Taheri

School of Civil, Environmental and Mining Engineering, The University of Adelaide, Adelaide SA 5005, Australia
Website | E-Mail
Interests: drilling performance; rock burst investigation; behaviour of cement paste backfill material; slope and underground opening stability; advanced laboratory and field testing methods; soil improvement methods
Guest Editor
Prof. Dr. Jixiong Zhang

State Key Laboratory of Coal Resources and Safe Mining, China University of Mining and Technology, Xuzhou 221116, China
Website | E-Mail
Interests: backfill mining; behaviour of backfill material; strata movement control; rock mechanics; hazards prevention induced by mining

Special Issue Information

Dear Colleagues,

Backfilling of mined-out areas is a fundamental component of many underground mining operations. The backfill material provides support to the surrounding rock mass, reduces wasteful dilution, enables a safe working area for production activities and mitigates the risk of surface subsidence. By combining tailing materials in backfill, it is possible to reduce the environmental footprint of the mine and assist with final site rehabilitation. Therefore, cemented paste backfill (CPB) has become an important component of underground mining operations. CPB is a mixture of tailings, water, and cement used to fill underground stopes. Reducing backfilling cost by decreasing cement content may increase ore dilution from poorly performing backfill exposures. Alternatively, increasing cement content will raise the costs; however, it could increase the productivity through improved mining system cycle times. To reduce the cost and keep the CBP strength at its required level, use of other binder materials can reduce the cost while maintaining its optimal strength performance. Moreover, the tailings particle size and density significantly alter the strength, microstructure, water demand and economic costs of backfill mixtures. In addition, CPB, solid waste backfilling has become popular in underground mining activities specially coal mining. In coal mining, backfilling of the gob area is performed in conjunction with mining operations. The properties of solid waste backfilled materials may significantly influence local strata behaviour. Therefore, assessment of the behaviour of backfill material under different in-situ stress conditions is of crucial importance. This Special Issue aims to bring together corresponding studies from all these areas including fundamental constitutive model studies, experimental studies, as well as analytical and numerical analyses, to characterize backfill material. We welcome studies on mine stability and mining operation issues in mining with backfill and backfill mining case studies.

The first round deadline is 30 November 2018.

Dr. Abbas Taheri
Prof. Dr. Jixiong Zhang
Guest Editors

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Keywords

  • Cement paste backfilling
  • Solid backfilling
  • Underground mining
  • Constitutive and numerical modelling
  • Experimental studies
  • Backfilling optimization
  • Mine operation

Published Papers (18 papers)

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Research

Open AccessArticle Influential Factors in Transportation and Mechanical Properties of Aeolian Sand-Based Cemented Filling Material
Minerals 2019, 9(2), 116; https://doi.org/10.3390/min9020116 (registering DOI)
Received: 24 January 2019 / Revised: 12 February 2019 / Accepted: 13 February 2019 / Published: 16 February 2019
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Abstract
Given that normal filling technology generally cannot be used for mining in the western part of China, as it has only a few sources for filling gangue, the feasibility of instead using cemented filling materials with aeolian sand as the aggregate is discussed [...] Read more.
Given that normal filling technology generally cannot be used for mining in the western part of China, as it has only a few sources for filling gangue, the feasibility of instead using cemented filling materials with aeolian sand as the aggregate is discussed in this study. We used laboratory tests to study how the fly ash (FA) content, cement content, lime–slag (LS) content, and concentration influence the transportation and mechanical properties of aeolian-sand-based cemented filling material. The internal microstructures and distributions of the elements in filled objects for curing times of 3 and 7 days are analyzed using scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). The experimental results show that: (i) the bleeding rate and slump of the filling-material slurry decrease gradually as the fly ash content, cement content, lime–slag content, and concentration increase, (ii) while the mechanical properties of the filled object increase. The optimal proportions for the aeolian sand-based cemented filling material include a concentration of 76%, a fly ash content of 47.5%, a cement content of 12.5%, a lime–slag content of 5%, and an aeolian sand content of 35%. The SEM observations show that the needle/rod-like ettringite (AFt) and amorphous and flocculent tobermorite (C-S-H) gel are the main early hydration products of a filled object with the above specific proportions. After increasing the curing time from 3 to 7 days, the AFt content decreases gradually, while the C-S-H content and the compactness increase. Full article
(This article belongs to the Special Issue Backfilling Materials for Underground Mining)
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Open AccessArticle An Innovative Method for Placement of Gangue Backfilling Material in Steep Underground Coal Mines
Minerals 2019, 9(2), 107; https://doi.org/10.3390/min9020107
Received: 17 January 2019 / Revised: 7 February 2019 / Accepted: 11 February 2019 / Published: 13 February 2019
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Abstract
Using gangue backfilling in underground coal mining not only controls the roof deformation in the gob area but also reduces the amount of mining waste rock. However, due to the limitations of the complicated engineering conditions, backfilling mining in the steep coal seam [...] Read more.
Using gangue backfilling in underground coal mining not only controls the roof deformation in the gob area but also reduces the amount of mining waste rock. However, due to the limitations of the complicated engineering conditions, backfilling mining in the steep coal seam is not widely applied. In this study, a long-distance backfilling technology with a scraper winch for a steep coal seam was proposed and applied in a flexible shield supporting working face in Datai Mine, Beijing. Aiming at the problem of the decreasing backfilling ratio in field practice, numerical simulation was carried out to research the moving law of gangue in the goaf. The gangue mainly experienced four stages: gangue landslide stage, small-scale subsidence stage, funnel-shaped subsidence stage, and large-scale subsidence stage. The moving area of the gangue could be divided into five areas including a motionless area, a landslide area, a subsidence area, a funnel-shaped subsidence area, and a to-be-backfilled area. With the increase of the inclined length of the working face, the moving time of the gangue increased gradually. Based on the simulation results, the scheme of backfilling and mining in Datai Mine was optimized, for which the inclined length of the working face was shortened, and a higher backfilling ratio was obtained. Full article
(This article belongs to the Special Issue Backfilling Materials for Underground Mining)
Open AccessArticle Experimental Research on Deformation Characteristics of Waste-Rock Material in Underground Backfill Mining
Minerals 2019, 9(2), 102; https://doi.org/10.3390/min9020102
Received: 2 January 2019 / Revised: 5 February 2019 / Accepted: 7 February 2019 / Published: 11 February 2019
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Abstract
Waste-rock material used in underground backfill mining has a granular texture and acquires non-linear deformation characteristics when compressed. The deformation modulus of waste-rock measured by a laboratory compression test is significantly different from the true deformation modulus in the field, due to the [...] Read more.
Waste-rock material used in underground backfill mining has a granular texture and acquires non-linear deformation characteristics when compressed. The deformation modulus of waste-rock measured by a laboratory compression test is significantly different from the true deformation modulus in the field, due to the complete confining effect of the loading steel cylinder. In this study, we performed a series of laboratory-based compression tests on waste-rock samples. The results showed that lab-acquired deformation modulus variations of waste rock could be divided into three stages: slow increase, accelerated increase, and rapid increase. We also measured the true deformation modulus of backfill waste rock by conducting a field test in gob areas of the Tangshan coal mine, China. The hardening process of backfill waste rock during the field test was analyzed, and could be divided into four stages: roof contact, rapid compression, slow compression, and long-term stable. With the increase of axial strain, the lab- and field-measured deformation moduli of waste rock both increased exponentially. A correction parameter was proposed to investigate the relationship between the field-generated true deformation modulus and the lab-tested deformation modulus. The correction parameter k positively correlated with the axial strain, in the form of an exponential function. The magnitude of k was between 0.5616 and 0.6531. Full article
(This article belongs to the Special Issue Backfilling Materials for Underground Mining)
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Open AccessArticle Experimental Investigation of Perceptual Characteristics of Functional Cemented Backfilling Materials in Coal Mines
Minerals 2019, 9(1), 55; https://doi.org/10.3390/min9010055
Received: 27 November 2018 / Revised: 2 January 2019 / Accepted: 3 January 2019 / Published: 17 January 2019
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Abstract
For investigating perceptual stress characteristics of Functional Cemented Backfilling Materials (FCBM) in coal mines, we prepared functional specimens based on Cemented Backfilling Materials (CBM) with the perceptual stress ability, and clarified their conductive mechanism, perceptual mechanism, and possible engineering applications. Using mechanical tests [...] Read more.
For investigating perceptual stress characteristics of Functional Cemented Backfilling Materials (FCBM) in coal mines, we prepared functional specimens based on Cemented Backfilling Materials (CBM) with the perceptual stress ability, and clarified their conductive mechanism, perceptual mechanism, and possible engineering applications. Using mechanical tests and the network parallel dynamic method, the mechanical and electrical properties of the prepared materials and the perceptual characteristics under mechanical–electric coupling conditions were analyzed in depth. The test results demonstrate that the deformation of FCBMs obey standard stress–strain rules, while the conductive phase addition can deteriorate their mechanical properties and simultaneously enhance the electrical conductivity of materials. Through fitting, the percolation threshold was determined to be 9.85%. Before the failure, the spatial distribution of the apparent resistivity in the materials was shown to follow the X-shaped radial pattern; after the failure, the material apparent resistivity obeys different distribution rules at various stages. The apparent resistivity of FCBM is negatively correlated with the strain value at the elastic and plastic stages and positively correlated with it at the failure stage. When the graphite content exceeds the percolation threshold, the materials exhibit a favorable perceptual functionality at the elastic stage. Full article
(This article belongs to the Special Issue Backfilling Materials for Underground Mining)
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Open AccessArticle Properties and Application of Backfill Materials in Coal Mines in China
Minerals 2019, 9(1), 53; https://doi.org/10.3390/min9010053
Received: 20 November 2018 / Revised: 25 December 2018 / Accepted: 9 January 2019 / Published: 17 January 2019
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Abstract
Coal is the basic resource underpinning energy generation in China, however, constant, large-scale mining of coal results in many problems such as ecological destruction of mining areas. As a result, backfilling of solid waste underground is proposed to control strata and surface subsidence [...] Read more.
Coal is the basic resource underpinning energy generation in China, however, constant, large-scale mining of coal results in many problems such as ecological destruction of mining areas. As a result, backfilling of solid waste underground is proposed to control strata and surface subsidence and to protect the environment. At present, these materials, such as granular material, cemented material and high-water-content materials are mainly used for backfilling. This study summarised the types of backfill materials that are used in coal mines in China along with the backfilling process. Moreover, distribution and characteristics of mines backfilled with these backfill materials were obtained and analysed. Considering the socio-environmental aspects that affect backfilling, this research proposed a guideline for the selection of backfill materials and then analysed specific engineering cases of three backfill materials. In addition, the future development of backfill materials was discussed. With extensive extraction of shallow coal resources in China and, therefore, rapid depletion of coal resources in eastern regions of China, coal mining depth is increasing significantly. As a result, it is required to investigate new backfill materials suited for the deep high-stress environment. Full article
(This article belongs to the Special Issue Backfilling Materials for Underground Mining)
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Open AccessArticle In Situ X-Ray CT Investigations of Meso-Damage Evolution of Cemented Waste Rock-Tailings Backfill (CWRTB) during Triaxial Deformation
Minerals 2019, 9(1), 52; https://doi.org/10.3390/min9010052
Received: 4 December 2018 / Revised: 3 January 2019 / Accepted: 6 January 2019 / Published: 16 January 2019
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Abstract
This work presents an experimental study that focused on the meso-damage evolution of cemented waste rock-tailing backfill (CWRTB) under triaxial compression using the in situ X-ray computed tomography (CT) technique. Although numerous investigations have studied the magnitude of the strength of CWRTB material, [...] Read more.
This work presents an experimental study that focused on the meso-damage evolution of cemented waste rock-tailing backfill (CWRTB) under triaxial compression using the in situ X-ray computed tomography (CT) technique. Although numerous investigations have studied the magnitude of the strength of CWRTB material, the mesoscopic damage evolution mechanisms under triaxial deformation are still poorly understood. Artificial CWRTB samples with a waste rock proportion of 30% were prepared by mixing tailings, waste rock, cement, and water. A specific self-developed loading device was used to match the CT machine to real-time CT scanning for the CWRTB sample. A series of 2D CT images were obtained by performing CT imaging at five key points throughout the test and from three positions in the sample. The CT values, for the purpose of meso-damage evolution in CWRTB, were identified. The results showed that the axial stress–strain curve presented strain hardening characteristics. The CT data revealed the inhomogeneous damage field inside the CWRTB sample and the most severely damaged regions that were usually located at the waste block-tailings paste interfaces. The changes in CT values for the different regions of interest (ROI) revealed the complicated interactions between the waste blocks and the tailings paste matrix. The meso-structural changes, formation of the localized bands, and the associated stress dilatancy phenomenon were strongly influenced by the interactions between the waste blocks and tailing paste. Full article
(This article belongs to the Special Issue Backfilling Materials for Underground Mining)
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Open AccessArticle Total and Effective Stresses in Backfilled Stopes during the Fill Placement on a Pervious Base for Barricade Design
Minerals 2019, 9(1), 38; https://doi.org/10.3390/min9010038
Received: 10 November 2018 / Revised: 30 December 2018 / Accepted: 7 January 2019 / Published: 11 January 2019
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Abstract
Backfill is increasingly used in underground mines worldwide. Its successful application depends on the stability of the barricades built at the base of the stopes to hold the backfill in place, which in turn depends on the knowledge of the pore water pressure [...] Read more.
Backfill is increasingly used in underground mines worldwide. Its successful application depends on the stability of the barricades built at the base of the stopes to hold the backfill in place, which in turn depends on the knowledge of the pore water pressure (PWP) and stresses during, or shortly after, the placement of the slurried backfill. Until now, self-weight consolidation is usually considered for the estimation of the PWP. There is no solution available to evaluate the total and effective stresses during, and shortly after, the filling operation. As excess PWP can simultaneously be generated (increased) and dissipated (decreased) during the backfilling operation, effective stresses can develop when the filling rate is low and/or hydraulic conductivity of the backfill is high. The arching effect has to be considered to evaluate the effective and total stresses in the backfilled stopes. In this paper, a pseudo-analytical solution is proposed to evaluate the effective and total stresses in backfilled stopes during the backfill deposition on a permeable base, by considering the self-weight consolidation and arching effect. The proposed solution is validated by numerical results obtained by Plaxis2D. A few sample applications of the proposed solution are shown. Full article
(This article belongs to the Special Issue Backfilling Materials for Underground Mining)
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Open AccessArticle Slurry Preparation Effects on the Cemented Phosphogypsum Backfill through an Orthogonal Experiment
Minerals 2019, 9(1), 31; https://doi.org/10.3390/min9010031
Received: 6 December 2018 / Revised: 2 January 2019 / Accepted: 8 January 2019 / Published: 10 January 2019
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Abstract
The cemented phosphogypsum (PG) backfill technique provides a new method for massive consumption of PG, and therefore alleviating the environmental pollution of PG. This study considered the effects of slurry preparation on the performance of cemented PG backfill. A L16(44 [...] Read more.
The cemented phosphogypsum (PG) backfill technique provides a new method for massive consumption of PG, and therefore alleviating the environmental pollution of PG. This study considered the effects of slurry preparation on the performance of cemented PG backfill. A L16(44) orthogonal experiment was designed to analyze four factors, namely the solid content, phosphogypsum-to-binder ratio (PG/B ratio), stirring time and stirring speed, with each factor having four levels. According to the range analysis, the solid content played the dominant role in controlling the bleeding rate, while the setting times strongly depended on the PG/B ratio. In terms of strength development of the backfill, the PG/B ratio was shown to be the most significant factor determining the unconfined compressive strength (UCS), followed by the solid content, stirring time and stirring speed. Furthermore, the results showed that the slurry preparation affected the environmental behavior of impurities that originated in PG. By analyzing the concentrations of impurities in the bleeding water of the slurry as well as the leachates of the tank leaching test, the results showed that the release of F and SO42− was aggravated clearly with the increase in the PG/B ratio, while the release of PO43− always remained at relatively low levels. Full article
(This article belongs to the Special Issue Backfilling Materials for Underground Mining)
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Open AccessFeature PaperArticle Application of Slag–Cement and Fly Ash for Strength Development in Cemented Paste Backfills
Minerals 2019, 9(1), 22; https://doi.org/10.3390/min9010022
Received: 25 October 2018 / Revised: 24 December 2018 / Accepted: 24 December 2018 / Published: 30 December 2018
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Abstract
The present study investigates the combined capacity of a newly developed slag-blended cement (MC) and fly ash (FA) as a sustainable solution towards improving the mechanical performance of the cemented paste backfill (CPB) system of a copper-gold underground mine. A total of thirteen [...] Read more.
The present study investigates the combined capacity of a newly developed slag-blended cement (MC) and fly ash (FA) as a sustainable solution towards improving the mechanical performance of the cemented paste backfill (CPB) system of a copper-gold underground mine. A total of thirteen mix designs consisting of three MC-treated and ten MC + FA-treated blends were examined. Samples were prepared with a solids content of 77% (by total mass), and were allowed to cure for 7, 14, 28, 56 and 128 days prior unconfined compression testing. Scanning electron microscopy (SEM) studies were also carried out to observe the evolution of fabric in response to MC and MC + FA amendments. The greater the MC content and/or the longer the curing period, the higher the developed strength, toughness and stiffness. The exhibited improvements, however, were only notable up to 56 days of curing, beyond of which the effect of curing was marginal. The performance of 4% Portland cement or PC (by total dry mass) was found to be similar to that of 1.5% MC, while the higher MC inclusions of 2.5% and 3%, though lower in terms of binder content, unanimously outperformed 4% PC. The use of FA alongside MC improved the bonding/connection interface generated between the tailings aggregates, and thus led to improved mechanical performance compared with similar MC inclusions containing no FA. Common strength criteria for CPBs were considered to assess the applicability of the newly introduced MC and MC + FA mix designs. The mix designs “3% MC” and “2.5% MC + 2–2.5% FA” satisfied the 700 kPa strength threshold required for stope stability, and thus were deemed as optimum design choices. Full article
(This article belongs to the Special Issue Backfilling Materials for Underground Mining)
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Open AccessArticle Influence of Lateral Loading on Compaction Characteristics of Crushed Waste Rock Used for Backfilling
Minerals 2018, 8(12), 552; https://doi.org/10.3390/min8120552
Received: 13 October 2018 / Revised: 18 November 2018 / Accepted: 19 November 2018 / Published: 28 November 2018
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Abstract
Crushed waste rock can be used as backfill in goafs to allow re-use of otherwise solid waste and to control surface subsidence. If a certain lateral stress is applied to crushed waste rocks beforehand, they are densified. Therefore, this research investigated the effects [...] Read more.
Crushed waste rock can be used as backfill in goafs to allow re-use of otherwise solid waste and to control surface subsidence. If a certain lateral stress is applied to crushed waste rocks beforehand, they are densified. Therefore, this research investigated the effects of lateral stress on compaction characteristics of waste rocks for backfilling by utilising a self-designed bidirectional loading test system for granular materials. Furthermore, this study tested the changes in the mechanical parameters on lateral and axial loading of waste rocks for backfilling and measured the influence of lateral stress on lateral strain, axial strain, porosity, and lateral pressure coefficient during compaction. The test results demonstrate that (1) lateral stress affects porosity, strain, and the lateral pressure coefficient of crushed waste rocks for backfilling in lateral and axial loading. (2) In lateral loading, the greater the lateral stress, the larger the lateral strain and the reduction in lateral porosity. (3) Under axial loading, for the samples on which a high lateral stress is applied, because the porosity of waste rocks is decreased in advance, the density increases, thus finally resulting in a lower axial strain. (4) After compaction, the particle size distributions of the samples of the crushed waste rocks under four lateral stresses all shift upwards compared with those before compaction, implying that particles are crushed. However, lateral stress does not reach the crushing strength of waste rock particles, which exerts only a small influence on the crushing of particles before and after compaction. Full article
(This article belongs to the Special Issue Backfilling Materials for Underground Mining)
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Open AccessArticle In Vivo X-ray Computed Tomography Investigations of Crack Damage Evolution of Cemented Waste Rock Backfills (CWRB) under Uniaxial Deformation
Minerals 2018, 8(11), 539; https://doi.org/10.3390/min8110539
Received: 15 October 2018 / Revised: 10 November 2018 / Accepted: 15 November 2018 / Published: 21 November 2018
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Abstract
Cemented waste rock backfill (CWRB), which is a mixture of tailings, waste rock, cement, and water, is subjected to combination actions in underground mining operations and has been widely used in deep resource mining. While the strength requirement and macroscopic deformation behaviors of [...] Read more.
Cemented waste rock backfill (CWRB), which is a mixture of tailings, waste rock, cement, and water, is subjected to combination actions in underground mining operations and has been widely used in deep resource mining. While the strength requirement and macroscopic deformation behaviors of CWRB have been well studied, the mesoscopic damage evolution mechanisms are still not well understood. In this work, a CWRB sample with a waste rock proportion of 30% was studied with a uniaxial compression test under tomographic monitoring, using a 450 kV industrial X-ray computed tomography (CT). Clear CT images, CT value analysis, crack identification, and extraction reveal that CWRB damage evolution is extremely inhomogeneous and affected by the waste rock size, shape, and distribution. Furthermore, the crack initiation, propagation, and coalescence behaviors are limited to the existing waste rocks. When deformation grows to a certain extent, the cracks demonstrate an interlocking phenomenon and their propagation paths are affected by the waste rocks, which may improve the ability to resist compressive deformation. Volumetric dilatancy caused by the damage and cracking behavior has closed a link with the meso-structural changes, which are controlled by the interactions between the waste rocks and the cemented tailing paste. Full article
(This article belongs to the Special Issue Backfilling Materials for Underground Mining)
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Open AccessArticle Particle Size Distribution of Cemented Rockfill Effects on Strata Stability in Filling Mining
Minerals 2018, 8(9), 407; https://doi.org/10.3390/min8090407
Received: 2 August 2018 / Revised: 25 August 2018 / Accepted: 11 September 2018 / Published: 14 September 2018
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Abstract
It is of great significance for engineering safety, economic benefits, environmental protection, and sustainable development to investigate the strata stability in filling mining with cemented rockfill. Consequently, this paper is based on a specific coal mine where we applied the fully-mechanized longwall mining [...] Read more.
It is of great significance for engineering safety, economic benefits, environmental protection, and sustainable development to investigate the strata stability in filling mining with cemented rockfill. Consequently, this paper is based on a specific coal mine where we applied the fully-mechanized longwall mining and filling and designed a cemented rockfill material for which the particles satisfied the Talbot gradation. Uniaxial and triaxial compression experiments were carried out on the cemented rockfill specimen, which obtained the relations between the mechanical parameters (Poisson ratio, elastic modulus, compressive strength, cohesive force, internal friction angle, and tensile strength) and the particle size distribution of the aggregate. The excavation and filling processes in the coal seam were simulated based on the numerical software FLAC3D. The characteristics of the displacement and stress fields of the strata when the goaf was filled by cemented rockfill with different granule gradations were discussed. The influences of the particle size distribution and mining distance on the maximum subsidence displacement of the coal seam roof, internal stress of the backfill, and the stress of the rock mass in the coalface were analyzed. The feasibility and effectiveness of the filling mining with cemented rockfill to protect the integrity of the overlying strata were discussed. The results showed that optimizing the particle size distribution of the aggregate in cemented rockfill could increase the loading capacity of the backfill to improve the filling effect, effectively control the strata movement, and decrease the stress of rock mass in the coalface to reduce the potential danger. Full article
(This article belongs to the Special Issue Backfilling Materials for Underground Mining)
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Open AccessArticle Effects of Superplasticizer on the Hydration, Consistency, and Strength Development of Cemented Paste Backfill
Minerals 2018, 8(9), 381; https://doi.org/10.3390/min8090381
Received: 23 July 2018 / Revised: 10 August 2018 / Accepted: 27 August 2018 / Published: 3 September 2018
Cited by 8 | PDF Full-text (4495 KB) | HTML Full-text | XML Full-text
Abstract
The strength and consistency of cemented paste backfill (CPB) are of key concerns in the stope stability and cost control for underground mines. It is common practice to use additives, such as superplasticizer, to improve the performance of CPB. This study mainly focuses [...] Read more.
The strength and consistency of cemented paste backfill (CPB) are of key concerns in the stope stability and cost control for underground mines. It is common practice to use additives, such as superplasticizer, to improve the performance of CPB. This study mainly focuses on the effects of superplasticizer on the hydration, consistency, and strength of CPB. In this study, a polynaphtalene sulfonate was used as the superplasticizer. The binder is a mix of 33.3% ordinary Portland cement and 66.7% fly ash. The CPB specimens with a tailings-binder ratio of 3:1 and a solid concentration of 70% were then tested by a low field nuclear magnetic resonance system after different hydration times. Effects of polynaphtalene sulfonate on the hydration, fluidity, and strength were investigated. Results showed that the polynaphtalene sulfonate has a strong influence on short-duration hydration, which may contribute to the strength increase of CPB. It has been demonstrated that the polynaphtalene sulfonate improved the fluidity of the CPB mixture. With the increased dosage of polynaphtalene sulfonate, the slump increased. It was also found that the polynaphtalene sulfonate dosage has a negligible effect on the 1 day (d) strength while it has a strengthening effect on the 7 d, 14 d, and 28 d strength of CPB specimens. Full article
(This article belongs to the Special Issue Backfilling Materials for Underground Mining)
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Open AccessArticle Evaluation of Viscosity, Strength and Microstructural Properties of Cemented Tailings Backfill
Minerals 2018, 8(8), 352; https://doi.org/10.3390/min8080352
Received: 9 July 2018 / Revised: 9 August 2018 / Accepted: 12 August 2018 / Published: 14 August 2018
Cited by 10 | PDF Full-text (4977 KB) | HTML Full-text | XML Full-text
Abstract
In this study, the particle size distribution and chemical composition of gold mine tailings were examined experimentally. A series of viscosity and uniaxial compressive strength (UCS) tests were used to study the relations between the viscosity of cemented tailings backfill (CTB) slurry, the [...] Read more.
In this study, the particle size distribution and chemical composition of gold mine tailings were examined experimentally. A series of viscosity and uniaxial compressive strength (UCS) tests were used to study the relations between the viscosity of cemented tailings backfill (CTB) slurry, the solid content (SD), and the cement-to-tailings ratio (c/t). Relations between UCS performance of CTB and SD, c/t, and curing time (CT) were discussed while examining the microstructure of 28-day cured backfill with different solid contents. Results illustrate that a major increase in CTB viscosity by increasing the SD leads to the formation of tailings grains for a skeleton formation, which is formed due to consolidation and gravitational forces. The CTB’s strength increases with the increase of c/t, SD, and CT, due to a decrease in water-to-cement ratio and porosity, and an increase in hydration products over time. The SEM micrographs show how CTB’s microstructure is affected by the SD, generating ettringites and calcium silicate hydrates in the backfill matrix. The findings of this study will lead to an efficient CTB mix design for reaching the higher performance in underground mining structures, thereby reducing expenses related to the backfill. Full article
(This article belongs to the Special Issue Backfilling Materials for Underground Mining)
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Open AccessArticle Particle Size Distribution Effects on the Strength Characteristic of Cemented Paste Backfill
Minerals 2018, 8(8), 322; https://doi.org/10.3390/min8080322
Received: 31 May 2018 / Revised: 10 July 2018 / Accepted: 25 July 2018 / Published: 27 July 2018
Cited by 7 | PDF Full-text (5370 KB) | HTML Full-text | XML Full-text
Abstract
It is of great significance, for economic, environmental and security reasons, to investigate the strength characteristic of underground cemented paste backfill (CPB). Consequently, an ultrasonic test, uniaxial and triaxial compression experiment, and acoustic emission (AE) monitoring were carried out on CPB, for which [...] Read more.
It is of great significance, for economic, environmental and security reasons, to investigate the strength characteristic of underground cemented paste backfill (CPB). Consequently, an ultrasonic test, uniaxial and triaxial compression experiment, and acoustic emission (AE) monitoring were carried out on CPB, for which the particles satisfied Talbot gradation. The homogeneity of CPB specimens was evaluated by ultrasonic pulse velocity (UPV). The stress–strain behavior and AE characteristic of CPB specimens under different Talbot indices and confining pressures were investigated. The effects of the particle size distribution and the confining pressure on the peak strength of CPB were analyzed. The strength parameter model of CPB under the coupled influence of the particle size distribution and the confining pressure was constructed based on the Mohr–Coulomb strength criterion. The results show that the peak strength of CPB is positively linear with confining pressure, however, the relationship between its strength parameters and the Talbot index can be characterized by a quadratic polynomial function. This suggests that there is an optimal gradation of particles reflected in the maximum strength of CPB. Full article
(This article belongs to the Special Issue Backfilling Materials for Underground Mining)
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Open AccessArticle Particle-Crushing Characteristics and Acoustic-Emission Patterns of Crushing Gangue Backfilling Material under Cyclic Loading
Minerals 2018, 8(6), 244; https://doi.org/10.3390/min8060244
Received: 13 May 2018 / Revised: 31 May 2018 / Accepted: 3 June 2018 / Published: 7 June 2018
Cited by 1 | PDF Full-text (5108 KB) | HTML Full-text | XML Full-text
Abstract
In solid backfilling coal mining (SBCM), the crushed gangue backfilling material (CGBM) is generally compacted circularly by a compaction machine in order to reduce its compressibility. In this cyclic compaction process, the particles are crushed, which has a significant effect on the deformation [...] Read more.
In solid backfilling coal mining (SBCM), the crushed gangue backfilling material (CGBM) is generally compacted circularly by a compaction machine in order to reduce its compressibility. In this cyclic compaction process, the particles are crushed, which has a significant effect on the deformation resistance of CGBM. However, the deformation resistance of CGBM is critical for controlling overburden strata movement and ground surface subsidence. This study implemented an experimental approach to investigate the particle-crushing characteristics and acoustic-emission (AE) characteristics of CGBM during constant-amplitude cyclic loading (CACL). At the same time, the relationship between particle crushing and AE signals was established. The results showed that the gangue particles were generally in the shape of irregular convex polyhedrons with more edges and angles that were prone to breakage. It also demonstrated that both the crushing ratio (Bg) and the newly produced fine granule content increased with the cyclic loading times. The content of newly generated fine particles can reflect the particle-crushing conditions to a certain extent. What is more, it was found that the CGBM samples exhibited an apparent Felicity effect during CACL, and AE signals were the most active during the first loading cycle. The crushing ratio of CGBM was highly correlated to the AE signals, which indicated that AE signals can be used to reflect the particle-crushing situation of CGBM. This study is of great significance for obtaining an in-depth understanding of the mechanical properties of CGBM, as well as providing guidance for the engineering practice of SBCM. Full article
(This article belongs to the Special Issue Backfilling Materials for Underground Mining)
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Open AccessArticle The Effect of Backfilling Materials on the Deformation of Coal and Rock Strata Containing Multiple Goaf: A Numerical Study
Minerals 2018, 8(6), 224; https://doi.org/10.3390/min8060224
Received: 25 April 2018 / Revised: 22 May 2018 / Accepted: 23 May 2018 / Published: 25 May 2018
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Abstract
Backfilling mining is thought to play a significant role in controlling the deformation of coal and rock strata and the distribution of underground pressure. This study presents a numerical investigation of the influence of the strength of backfilling materials (BMS) on the deformation [...] Read more.
Backfilling mining is thought to play a significant role in controlling the deformation of coal and rock strata and the distribution of underground pressure. This study presents a numerical investigation of the influence of the strength of backfilling materials (BMS) on the deformation of coal and rock strata consisting of multiple goaf during excavation using the backfill mining method. In this study, a numerical three-dimensional fast Lagrangian analysis of continua (FLAC 3D) model was constructed to explore the relationship among the BMS, the displacement of coal and rock strata, and the distribution of underground pressure based on the geological conditions of a mining panel of the Hengda coal mine in the City of Fuxin, China. The numerical results suggest that as the BMS increase, the supporting ability of backfilling materials in goaf becomes stronger. At the same time, when the displacement of coal and rock strata decrease, the pressure on the surrounding rocks decreases and the pressure on the overlying stratum increases. However, the effect of BMS on the coal and rock strata has a limit. When the BMS equals and/or exceeds that of coal, the influence is not obvious. In addition, the displacement and underground pressure in the surrounding goaf are also affected, but in a relatively gentle way. Moreover, during the process of mining, as the BMS increases, the scope and arch area of the underground pressure in front of working face decrease instead. The higher the BMS is, the more stable the main key stratum is. The ability to resist compressional deformation of backfilling materials plays an important role in controlling the displacement of roof and relieving the underground pressure on the overlying stratum. Thereby, the roof stability in front of the working face is helpful for safety in the production of coal mines. Full article
(This article belongs to the Special Issue Backfilling Materials for Underground Mining)
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Open AccessArticle Strength Development and Microstructure Evolution of Cemented Tailings Backfill Containing Different Binder Types and Contents
Minerals 2018, 8(4), 167; https://doi.org/10.3390/min8040167
Received: 20 March 2018 / Revised: 16 April 2018 / Accepted: 17 April 2018 / Published: 19 April 2018
Cited by 7 | PDF Full-text (36264 KB) | HTML Full-text | XML Full-text
Abstract
The microstructure evolution and strength development of cemented tailings backfill (CTB), mixed with plant tailings and cement, is critical to a more thorough and complete understanding of its functionality as a support structure in underground mining operations. Here, an experimental study is conducted [...] Read more.
The microstructure evolution and strength development of cemented tailings backfill (CTB), mixed with plant tailings and cement, is critical to a more thorough and complete understanding of its functionality as a support structure in underground mining operations. Here, an experimental study is conducted to investigate the effect of the solid contents of tailings, binder proportion, and type of cement reagent on unconfined compressive strength (UCS) and microstructure evolution with respect to a 90-day curing time. The results indicate that the mechanical strength gain is proportionally associated with increased binder and solid content. Besides, the samples prepared with 70 wt % solid content and a 25 wt % binder/tailings ratio have a maximum UCS of 6.26 MPa at a curing time of 90 days. In addition, it is also concluded that the binder proportion promotes the strength acquisition of CTB samples. Specifically, the 90-day UCS of the CTB with solid content of 68 wt % and binder content of 25 wt % is approximately twice that of the CTB with a 12.5 wt % binder proportion. Slag cement (Binder B1) and slag cement with 5 wt % NaOH (Binder B2) are used as admixture to replace the cement reagent; the results show that Binder B2 has more advantages than Binder B1 and Portland cement, and is a suitable cementing material for the CTB technology in the Daye Iron Mine. The microstructure is dominated by the network of hydration products and distribution of the pore, and hydrated material is significantly influenced by the curing time. The tailings particles are enclosed by the hydration products, and randomly disperse within their matrix at curing time of 90 days. Finally, the UCSs of CTB samples are observed to significantly increase with the increase in the curing time. Full article
(This article belongs to the Special Issue Backfilling Materials for Underground Mining)
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