Research

12 pages, 1790 KiB

Open AccessArticle

Optimization of Parameters for Rheological Properties and Strength of Cemented Paste Backfill Blended with Coarse Aggregates

by Jiandong Wang, Aixiang Wu, Zhuen Ruan, Raimund Bürger, Yiming Wang, Shaoyong Wang, Pingfa Zhang and Zhaoquan Gao

Minerals 2022, 12(3), 374; https://doi.org/10.3390/min12030374 - 18 Mar 2022

Cited by 7 | Viewed by 1908

Abstract

Cemented paste backfill (CPB) technology is widely used for environmental protection and underground goaf treatment. The influences of solid concentration, coarse aggregates dosage, and cement dosage on the rheological properties and compressive strength of CPB blended with coarse aggregates (CA-CPB) are investigated through [...] Read more.

Cemented paste backfill (CPB) technology is widely used for environmental protection and underground goaf treatment. The influences of solid concentration, coarse aggregates dosage, and cement dosage on the rheological properties and compressive strength of CPB blended with coarse aggregates (CA-CPB) are investigated through three-factor and four-level orthogonal experiments. The dynamic shear stress and plastic viscosity are selected to characterize the rheological properties of CA-CPB. The uniaxial compressive strength (UCS) is used to describe the compressive strength. The effect of each factor on rheological properties is different from that on UCS. The most significant influences on rheological properties and UCS are solid concentration and cement dosage, respectively. The optimal levels of each factor for rheological properties and UCS are different, resulting in different optimal combinations obtained through range analysis. Therefore, the overall desirability function approach is employed to perform multiple response optimization. The optimal parameters for high fluidity and strength obtained provide valuable information for the CA-CPB process in the Chifeng Baiyinnuoer Lead and Zinc Mine. Full article

(This article belongs to the Special Issue Backfilling Materials for Underground Mining, Volume II)

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17 pages, 6008 KiB

Open AccessArticle

Scale Effect of Filling on Overburden Migration in Local Filling Stope of Longwall Face in Steeply Dipping Coal Seam

by Shidong Wang, Wenyu Lv, Wenzhong Zhang, Juan Fan, Ankun Luo, Kaipeng Zhu and Kai Guo

Minerals 2022, 12(3), 319; https://doi.org/10.3390/min12030319 - 04 Mar 2022

Cited by 5 | Viewed by 1749

Abstract

The gangue filling mining method is used to reduce the occurrence of dynamic disasters on the roof of a steeply dipping coal seam (SDCS) effectively and improve the stability of the overburden structure. To comprehensively study the movement law of the overburden under [...] Read more.

The gangue filling mining method is used to reduce the occurrence of dynamic disasters on the roof of a steeply dipping coal seam (SDCS) effectively and improve the stability of the overburden structure. To comprehensively study the movement law of the overburden under different filling quantities, the 3221 working face of the Lvshuidong coal mine was taken as the research site. The vertical displacement, vertical stress, and plastic zone of the overburden under different filling quantities were analyzed by using FLAC3D numerical simulation and physical similarity simulations. The results show that the maximum stress in the stress concentration zone decreased with the increase of filling size. The vertical stress range of the overburden and floor in the filling zone increased significantly. The affected zones of the vertical displacement of the roof and floor and the vertical displacement of the overburden were reduced to varying degrees. The overall plastic zone was shrinking. The movement of overburden was well-controlled as the proportion of the fillings increased. The results of this study can provide an important reference for the stability control of the roof of SDCS filling mining. Full article

(This article belongs to the Special Issue Backfilling Materials for Underground Mining, Volume II)

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16 pages, 4596 KiB

Open AccessArticle

Stability Evaluation of Layered Backfill Considering Filling Interval, Backfill Strength and Creep Behavior

by Chongchong Qi, Li Guo, Yu Wu, Qinli Zhang and Qiusong Chen

Minerals 2022, 12(2), 271; https://doi.org/10.3390/min12020271 - 21 Feb 2022

Cited by 12 | Viewed by 1845

Abstract

Cemented paste backfill (CPB) is the primary solution to improving the safety of continuous mining. The interaction between rock mass and backfill is an important indicator of backfill stability. The creep behavior of weak rock mass is an essential factor, which causes the [...] Read more.

Cemented paste backfill (CPB) is the primary solution to improving the safety of continuous mining. The interaction between rock mass and backfill is an important indicator of backfill stability. The creep behavior of weak rock mass is an essential factor, which causes the evolution of stresses and displacements in the backfill stope. In this paper, numerical models were constructed to analyze the interactions between rock mass and backfill by considering the creep behavior of the rock mass, filling interval, and backfill strength. The numerical simulation results showed the effects of different parameters, including the number of backfilling layers, filling interval time (FIT), and backfill strength under creep behavior on stress, displacements, and plastic deformation. The horizontal displacement near the mid-height and vertical displacement at the top of the backfilled stope is the largest compared to layered backfilling. The stress within the backfilled stope is smallest when the stope is filled in a single layer. With increasing FIT, stress in the backfilled stope decreases. FIT mainly affected the horizontal displacement of the stope. The stresses on the stope bottom decrease when the strength of the middle-backfilled stope decreases. Overall, this study provides important insights for understanding the creep behavior of rock mass in underground backfilling practices. Full article

(This article belongs to the Special Issue Backfilling Materials for Underground Mining, Volume II)

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22 pages, 8188 KiB

Open AccessArticle

Three-Dimensional Quantitative Recognition of Filler Materials Ahead of a Tunnel Face via Time-Energy Density Analysis of Wavelet Transforms

by Sheng Zhang, Liang Zhang, Wenchao He, Tonghua Ling, Zongwei Deng and Guihai Fu

Minerals 2022, 12(2), 234; https://doi.org/10.3390/min12020234 - 11 Feb 2022

Cited by 13 | Viewed by 1391

Abstract

Advanced geological prediction of tunnels has become an indispensable task to ensure the safety and effectiveness of tunnel construction before excavation in karst areas. Geological disasters caused by unfavorable geological conditions, such as karst caves, faults, and broken zones ahead of a tunnel [...] Read more.

Advanced geological prediction of tunnels has become an indispensable task to ensure the safety and effectiveness of tunnel construction before excavation in karst areas. Geological disasters caused by unfavorable geological conditions, such as karst caves, faults, and broken zones ahead of a tunnel face, are highly sudden and destructive. Determining how to predict the spatial location and geometric size of unfavorable geological bodies accurately is a challenging problem. In order to facilitate a three-dimensional quantitative analysis of the filler material ahead of the tunnel face, a biorthogonal wavelet with short support, linear phase, and highly matching waveform of ground penetrating radar (GPR) wavelet is constructed by lifting a simple and general initial filter on the basis of lifting wavelet theory. A method for a time-energy density analysis of wavelet transforms (TEDAWT) is proposed in accordance with the biorthogonal wavelet. Fifteen longitudinal and horizontal survey lines are used to detect void fillers of different heights. Then, static correction, DC bias, gain, band-pass filtering, and offset processing are performed in the original GPR profile to enhance reflected signals and converge diffraction signals. A slice map of GPR profile is generated in accordance with the relative position of longitudinal and horizontal survey lines in space. The wavelet transform analysis of a single-channel signal of each survey line is performed by adopting the TEDAWT method because of the similar rule of the single-channel signal of GPR on the waveform overlay and the ability of the constructed wavelet basis to highlight the time-frequency characteristics of GPR signals. The characteristic value points of the first and second interfaces of the void fillers can be clearly determined, and the three-dimensional spatial position and geometric sizes of different void fillers can be obtained. Therefore, the three-dimensional visualization of GPR data is realized. Results show that the TEDAWT method has a good practical application effect in the quantitative identification of void fillers, which provides a basis for the interpretation of advanced geological prediction data of tunnels and for the construction decision. Full article

(This article belongs to the Special Issue Backfilling Materials for Underground Mining, Volume II)

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18 pages, 10140 KiB

Open AccessArticle

Application of Numerical Simulation Methods in Solving Complex Mining Engineering Problems in Dingxi Mine, China

by Boyi Hu, Qinli Zhang, Shuai Li, Haoxuan Yu, Xinmin Wang and Hao Wang

Minerals 2022, 12(2), 123; https://doi.org/10.3390/min12020123 - 21 Jan 2022

Cited by 9 | Viewed by 2475

Abstract

In the mining industry, with numerical simulation analysis of stope roof stability, stope exposed area computation, and pillar buckling collapse simulation, backfill body creep damage mechanism research is becoming the most popular method in the field of backfill mining techniques. In this paper, [...] Read more.

In the mining industry, with numerical simulation analysis of stope roof stability, stope exposed area computation, and pillar buckling collapse simulation, backfill body creep damage mechanism research is becoming the most popular method in the field of backfill mining techniques. In this paper, we first summarized and analyzed the current application status and the existing problems of numerical simulation for solving mining engineering technical problems; then, based on the practical engineering problems of mining phosphate rock resources under high and steep rock slopes (HSRS), we carried out a true-3D numerical simulation study for different underground mining methods, to determine the appropriate mining method. Therefore, this paper, taking Dingxi Mine in China as an example, highlights the advantages of the backfill mining method with a high and steep slope; meanwhile, it also points out how to improve the accuracy of a numerical simulation and make it more consistent with the actual situation of the mining engineering application site. This paper only serves as a guide, in order to start a conversation, and we hope many more experts and scholars will become interested and engaged in this field of research. Full article

(This article belongs to the Special Issue Backfilling Materials for Underground Mining, Volume II)

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18 pages, 5800 KiB

Open AccessArticle

Insight into Saturated Hydraulic Conductivity of Cemented Paste Backfill Containing Polycarboxylate Ether-Based Superplasticizer

by Sada Haruna and Mamadou Fall

Minerals 2022, 12(1), 93; https://doi.org/10.3390/min12010093 - 14 Jan 2022

Cited by 3 | Viewed by 1514

Abstract

Recycling of tailings in the form of cemented paste backfill (CPB) is a widely adopted practice in the mining industry. Environmental performance is an important design criterion of CPB structures. This environmental performance of CPB is strongly influenced by its saturated hydraulic conductivity [...] Read more.

Recycling of tailings in the form of cemented paste backfill (CPB) is a widely adopted practice in the mining industry. Environmental performance is an important design criterion of CPB structures. This environmental performance of CPB is strongly influenced by its saturated hydraulic conductivity (permeability). Superplasticizers are usually added to improve flowability, but there is a limited understanding of their influence on the hydraulic properties of the CPB. This paper presents new experimental results on the variations of the hydraulic conductivity of CPB containing polycarboxylate-based superplasticizer with different compositions and curing conditions. It is found that the hydraulic conductivity of the CPB decreases with the addition of superplasticizer, which is beneficial to its environmental performance. The reduction is largely attributable to the influence of the ether-based superplasticizer on particles mobility and cement hydration. Moreover, both curing temperature and time have correlations with the hydraulic conductivity of CPB containing superplasticizer. In addition, the presence of sulfate and partial replacement of PCI with blast furnace slag reduces the hydraulic conductivity. The variations are mainly due to the changes in the pore structure of the CPB. The new results discussed in this manuscript will contribute to the design of more environmental-friendly CPBs, which is essential for sustainable mining. Full article

(This article belongs to the Special Issue Backfilling Materials for Underground Mining, Volume II)

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16 pages, 4857 KiB

Open AccessArticle

The Recent Progress China Has Made in the Backfill Mining Method, Part III: Practical Engineering Problems in Stope and Goaf Backfill

by Haoxuan Yu, Shuai Li and Xinmin Wang

Minerals 2022, 12(1), 88; https://doi.org/10.3390/min12010088 - 13 Jan 2022

Cited by 9 | Viewed by 1868

Abstract

With the continuous innovation and development of science and technology, the mining industry has also benefited greatly and improved over time, especially in the field of backfill mining. Mining researchers are increasingly working on cutting-edge technologies, such as applying artificial intelligence to mining [...] Read more.

With the continuous innovation and development of science and technology, the mining industry has also benefited greatly and improved over time, especially in the field of backfill mining. Mining researchers are increasingly working on cutting-edge technologies, such as applying artificial intelligence to mining production. However, in addition, some problems in the actual engineering are worth people’s attention, and especially in China, such a big mining country, the actual engineering faces many problems. In recent years, Chinese mining researchers have conducted a lot of studies on practical engineering problems in the stope and goaf of backfill mining method in China, among which the three most important points are (1) Calculation problems of backfill slurry transportation; (2) Reliability analysis of backfill pipeline system; (3) Stope backfill process and technology. Therefore, this final part (Part III) will launch the research progress of China’s practical engineering problems from the above two points. Finally, we claim that Part III serves just as a guide to starting a conversation, and hope that many more experts and scholars will be interested and engage in the research of this field. Full article

(This article belongs to the Special Issue Backfilling Materials for Underground Mining, Volume II)

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15 pages, 7399 KiB

Open AccessArticle

A Population Balance Model for Shear-Induced Polymer-Bridging Flocculation of Total Tailings

by Zhuen Ruan, Aixiang Wu, Raimund Bürger, Fernando Betancourt, Rafael Ordoñez, Jiandong Wang, Shaoyong Wang and Yong Wang

Minerals 2022, 12(1), 40; https://doi.org/10.3390/min12010040 - 28 Dec 2021

Cited by 7 | Viewed by 1806

Abstract

Shear-induced polymer-bridging flocculation is widely used in the solid–liquid separation process in cemented paste backfill, beneficial to water recycling and tailings management in metal mines. A flocculation kinetics model based on Population Balance Model (PBM) is proposed to model the polymer-bridging flocculation process [...] Read more.

Shear-induced polymer-bridging flocculation is widely used in the solid–liquid separation process in cemented paste backfill, beneficial to water recycling and tailings management in metal mines. A flocculation kinetics model based on Population Balance Model (PBM) is proposed to model the polymer-bridging flocculation process of total tailings. The PBM leads to a system of ordinary differential equations describing the evolution of the size distribution, and incorporates an aggregation kernel and a breakage kernel. In the aggregation kernel, a collision frequency model describes the particle collision under the combined effects of Brownian motions, shear flow, and differential sedimentation. A semi-empirical collision efficiency model with three fitting parameters is applied. In the breakage kernel, a new breakage rate coefficient model with another three fitting parameters is introduced. Values of the six fitting parameters are determined by minimizing the difference between experimental data obtained from FBRM and modeling result through particle swarm global optimization. All of the six fitting parameters vary with flocculation conditions. The six fitting parameters are regressed with the flocculation factors with six regression models obtained. The validation modeling demonstrates that the proposed PBM quantifies well the dynamic evolution of the floc size during flocculation under the given experimental setup. The investigation will provide significant new insights into the flocculation kinetics of total tailings and lay a foundation for studying the performance of the feedwell of a gravity thickener. Full article

(This article belongs to the Special Issue Backfilling Materials for Underground Mining, Volume II)

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12 pages, 59824 KiB

Open AccessEditor’s ChoiceArticle

Characterization of Macro Mechanical Properties and Microstructures of Cement-Based Composites Prepared from Fly Ash, Gypsum and Steel Slag

by Jiajian Li, Shuai Cao and Erol Yilmaz

Minerals 2022, 12(1), 6; https://doi.org/10.3390/min12010006 - 21 Dec 2021

Cited by 40 | Viewed by 3143

Abstract

Using solid wastes (SWs) as backfilling material to fill underground mined-out areas (UMOAs) solved the environmental problems caused by SWs and reduced the backfilling cost. In this study, fly ash (FA), gypsum and steel slag (SS) were used to prepare cement-based composites (CBC). [...] Read more.

Using solid wastes (SWs) as backfilling material to fill underground mined-out areas (UMOAs) solved the environmental problems caused by SWs and reduced the backfilling cost. In this study, fly ash (FA), gypsum and steel slag (SS) were used to prepare cement-based composites (CBC). The uniaxial compression, computed tomography (CT) and scanning electron microscope (SEM) laboratory experiments were conducted to explore the macro and micromechanical properties of CBC. The findings showed that the uniaxial compressive strength (UCS) of CBC with a curing time of 7 d could reach 6.54 MPa. The increase of SS content reduced the UCS of CBC, while the gypsum and FA content could increase the UCS of CBC. Microscopic studies have shown that the SS particles in CBC have noticeable sedimentation, and the increase of SS content causes the failure mode of CBC from tensile to tensile-shear. These research results can provide a scientific reference for the preparation of backfilling materials. Full article

(This article belongs to the Special Issue Backfilling Materials for Underground Mining, Volume II)

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14 pages, 6028 KiB

Open AccessFeature PaperArticle

The Recent Progress China Has Made in the Backfill Mining Method, Part II: The Composition and Typical Examples of Backfill Systems

by Shuai Li, Zeming Zhao, Haoxuan Yu and Xinmin Wang

Minerals 2021, 11(12), 1362; https://doi.org/10.3390/min11121362 - 02 Dec 2021

Cited by 20 | Viewed by 3529

Abstract

The backfill mining method is a widely used mining method in the major mines of China, which can maximize the recovery of mineral resources and protect the environment. Currently, major mines in China are starting to build backfill systems to apply the backfill [...] Read more.

The backfill mining method is a widely used mining method in the major mines of China, which can maximize the recovery of mineral resources and protect the environment. Currently, major mines in China are starting to build backfill systems to apply the backfill mining method, therefore, Part II reviews the progress China has made on creating backfill systems, of which the main contents include: (1) Composition of the backfill system common in Chinese mines; (2) Typical examples of the backfill system in China. Finally, Part II serves as a guide to begin a conversation, and to encourage experts and scholars to engage in the research of this field. Full article

(This article belongs to the Special Issue Backfilling Materials for Underground Mining, Volume II)

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18 pages, 33757 KiB

Open AccessArticle

The Recent Progress China Has Made in the Backfill Mining Method, Part I: The Theory and Equipment of Backfill Pipeline Transportation

by Haoxuan Yu, Shuai Li and Xinmin Wang

Minerals 2021, 11(11), 1274; https://doi.org/10.3390/min11111274 - 17 Nov 2021

Cited by 17 | Viewed by 2751

Abstract

The backfill mining method is one of the common methods of mine mining worldwide, due to its capacity to maximize the recovery of mineral resources and protect the underground and the surface environment. Similar to the developing conditions of China’s mining industry, China’s [...] Read more.

The backfill mining method is one of the common methods of mine mining worldwide, due to its capacity to maximize the recovery of mineral resources and protect the underground and the surface environment. Similar to the developing conditions of China’s mining industry, China’s backfill mining technology started late, and the level of its equipment is weak, but its development is particularly rapid. Especially after entering the 21st century, China has paid more attention to mining safety, environmental protection, and the continuous implementation of resources development, China’s backfill mining method has increasingly improved, and the level of filling equipment has gradually reached the most advanced level worldwide, which means China has been making great progress in the equipment of backfill mining method, and in recent years, China has also made great progress in the theory of backfill pipeline transportation. Therefore, Part I mainly focuses on both the theory and equipment of backfill pipeline transportation and the recent progress China has made in is introduced in two sections as follows: (1) the theory of backfill pipeline transportation and (2) the equipment of the backfill mining method. Finally, the authors claim that this paper serves just as a guide, tossing out a brick to get a jade gem, and we hope many more experts and scholars will be interested and engage in the research of this field. Full article

(This article belongs to the Special Issue Backfilling Materials for Underground Mining, Volume II)

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19 pages, 1986 KiB

Open AccessEditor’s ChoiceArticle

Specific Mixing Energy of Cemented Paste Backfill, Part I: Laboratory Determination and Influence on the Consistency

by Reagan Kabanga Dikonda, Mamert Mbonimpa and Tikou Belem

Minerals 2021, 11(11), 1165; https://doi.org/10.3390/min11111165 - 21 Oct 2021

Cited by 1 | Viewed by 1655

Abstract

Slump determination is widely used to assess the consistency and transportability of fresh cemented paste backfill (CPB). CPB consistency can depend on the mixing procedure for CPB preparation. In this paper, a method was developed to determine the specific mixing energy (SME) that [...] Read more.

Slump determination is widely used to assess the consistency and transportability of fresh cemented paste backfill (CPB). CPB consistency can depend on the mixing procedure for CPB preparation. In this paper, a method was developed to determine the specific mixing energy (SME) that is dissipated during the preparation of CPB mixtures and to analyze its effect on CPB consistency. For this purpose, CPB recipes were prepared using two tailings and the mixing parameters (mixing time and speed and load mass) were successively varied. SME was determined for each mixture using a power meter equipped with an energy recording system mounted on a laboratory Omcan mixer. Slump was also determined for each mixture. A semi-empirical model was then developed to predict SME as a function of the mixing parameters. Results showed that predicted SME compared well with measured SME during CPB preparation. Results also showed that slump increased with increasing SME. The influence of SME on the rheological and mechanical properties of CPB and practical applications are presented in a companion paper. Full article

(This article belongs to the Special Issue Backfilling Materials for Underground Mining, Volume II)

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20 pages, 2147 KiB

Open AccessArticle

Specific Mixing Energy of Cemented Paste Backfill, Part II: Influence on the Rheological and Mechanical Properties and Practical Applications

by Reagan Kabanga Dikonda, Mamert Mbonimpa and Tikou Belem

Minerals 2021, 11(11), 1159; https://doi.org/10.3390/min11111159 - 21 Oct 2021

Cited by 3 | Viewed by 1510

Abstract

The rheological properties (yield stress, flow index and infinite dynamic viscosity) and mechanical properties (unconfined compressive strength, UCS) of different cemented paste backfill (CPB) recipes must be determined during the laboratory optimization phase. However, the influence of the mixing procedure on these properties [...] Read more.

The rheological properties (yield stress, flow index and infinite dynamic viscosity) and mechanical properties (unconfined compressive strength, UCS) of different cemented paste backfill (CPB) recipes must be determined during the laboratory optimization phase. However, the influence of the mixing procedure on these properties has scarcely been studied so far. The objective of this paper is to assess to what extent these properties depend on the specific mixing energy (SME) for a given type of mixer. CPB recipes were prepared based on two types of tailing (CPB-T1 and CPB-T2, also referred to as T1 and T2) at a fixed solid percentage for each type of tailing using the Omcan laboratory mixer. A mixture of 80% slag and 20% GU was used as a binder. The mixing time and the rotation speed of the mixer were successively varied. For each recipe prepared, we determined the SME, the rheological properties of fresh CPB (at the end of mixing) and the UCS at 7, 28 and 90 days of curing. The results show that yield stress and infinite viscosity decreased when SME increased in an interval going from 0.3 to 3.8 Wh/kg and 0.6 to 6 Wh/kg for CPB-T1 and CPB-T2, respectively. An increasing trend in UCS with increasing SME was also observed. Empirical equations describing the change of the rheological properties with the SME are used to estimate the change in rheological properties of CPB along the distribution system, considering the specific energy dissipation during CPB transportation. A mixing procedure for obtaining CPB mixtures that are representative of CPB deposited in underground mine stopes is suggested for laboratories who currently use a same mixing procedure, irrespective of the variable field specific energy. Full article

(This article belongs to the Special Issue Backfilling Materials for Underground Mining, Volume II)

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17 pages, 6505 KiB

Open AccessEditor’s ChoiceArticle

The Effect of Curing under Applied Stress on the Mechanical Performance of Cement Paste Backfill

by Yue Zhao, Abbas Taheri, Murat Karakus, An Deng and Lijie Guo

Minerals 2021, 11(10), 1107; https://doi.org/10.3390/min11101107 - 09 Oct 2021

Cited by 10 | Viewed by 2027

Abstract

After placing the Cement Paste Backfill (CPB) slurry in mined cavities underground, during the setting and hardening processes, the weight and hydrostatic pressure of the upper-layer CPB slurry applies an axial load over the bottom-layer CPB materials, which is called the self-consolidation of [...] Read more.

After placing the Cement Paste Backfill (CPB) slurry in mined cavities underground, during the setting and hardening processes, the weight and hydrostatic pressure of the upper-layer CPB slurry applies an axial load over the bottom-layer CPB materials, which is called the self-consolidation of CPB slurry. Due to this phenomenon, the mechanical properties of in situ CPB could be considerably different from laboratory results. Hence, it is crucial to understand the effect of self-consolidation behaviour on the mechanical properties of backfill material. This paper presents an experimental study on the impact of axial applied stress (A_s) during curing, which represents the various self-consolidation conditions and curing times on the mechanical properties of CPB material prepared using the tailings of a copper mine in South Australia and a newly released commercially manufactured cement called Minecem (MC). A curing under pressure apparatus (CPA) is designed to cure CPB samples under axial applied stress. The equipment can apply and measure axial load during curing and measure the passive lateral stress due to axial load which represents the horizontal stresses at a certain depth of CPB stope on the retaining structure. The prepared samples with axially applied pressure during curing were tested under uniaxial and triaxial compressive loading conditions. Microstructural tests by scanning electron microscopy (SEM) were also used to study the fabric evolution in response to various applied stresses during curing. Overall, the increase in A_s during curing leads to higher resultant CPB peak strength and stiffness under uniaxial and triaxial compression tests. For instance, a sample cured under 3.6 MPa axial load for 28 days demonstrates a uniaxial compressive strength (UCS) value of five times more than a sample cured under atmospheric curing conditions. Passive lateral stress was measured during the curing period and was representative of underground barricade stress. Furthermore, during curing, the axial applied stress changed the initial CPB pore structure after placement. With the increase in applied stress, the stress compressed CPB samples at the macroscale, leading to much smaller pores or cracks prior to the hydration process. At an early stage, the increase in UCS due to axial applied stress mainly arises from a dense microstructure caused by the compression of tailings and cement particles. With the increase in curing time, the observation also shows that a CPB matrix with fewer pore spaces may improve the hydration progress; hence, the influence of axial applied stress becomes more pronounced in long-term UCS. Full article

(This article belongs to the Special Issue Backfilling Materials for Underground Mining, Volume II)

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18 pages, 2612 KiB

Open AccessEditor’s ChoiceArticle

Substitution of Cement with Granulated Blast Furnace Slag in Cemented Paste Backfill: Evaluation of Technical and Chemical Properties

by Soili Solismaa, Akseli Torppa, Jukka Kuva, Pasi Heikkilä, Simo Hyvönen, Petri Juntunen, Mostafa Benzaazoua and Tommi Kauppila

Minerals 2021, 11(10), 1068; https://doi.org/10.3390/min11101068 - 29 Sep 2021

Cited by 9 | Viewed by 3239

Abstract

Cemented paste backfill (CPB) offers an environmentally sustainable way to utilize mine tailings, one of the largest waste streams in the world. CPB is a support and filler material used in underground mine cavities, which consists of mine tailings, water, and binder material [...] Read more.

Cemented paste backfill (CPB) offers an environmentally sustainable way to utilize mine tailings, one of the largest waste streams in the world. CPB is a support and filler material used in underground mine cavities, which consists of mine tailings, water, and binder material that usually is cement. Replacing cement with secondary raw materials like granulated blast-furnace slag reduces the total CO₂ emissions and strengthens the internal microstructure of the CPB. This study characterizes the total- and soluble contents of CPB starting materials and five CPB specimens containing different levels of slag substitution. In addition, phase composition (mineral liberation analysis, MLA) and internal structure (X-ray tomography) of five CPB specimens is documented, and measurements of compressive strength are used to evaluate their suitability as backfill material. Mine tailings and CPB specimens used in this study are rich in sulphates and arsenic, but low in sulphides. Stronger As leaching of ground CPB specimens compared with ground mine tailings is related to the elevating pore water pH during the cement hydration. The hydration product ettringite is found in all CPB specimens and its content is the lowest in the slag containing specimens. X-ray tomography revealed vertically differentiated density structures in the CPB specimens. The lower parts of all specimens are denser in comparison with the upper parts, which is probably due to the compaction of the solid particles at the base. The compressive strength test results indicate that partial substitution of cement with slag improves the strength of the CPB. The total replacement of cement with slag reduces the early strength but gives excellent strength and lower porosity over longer time intervals. The results of the study can be utilized in developing more durable and environmentally responsible CPB recipes for gold mines of similar mineral composition and gold extraction method. Full article

(This article belongs to the Special Issue Backfilling Materials for Underground Mining, Volume II)

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15 pages, 4593 KiB

Open AccessArticle

Feasibility of Recycling Bayer Process Red Mud for the Safety Backfill Mining of Layered Soft Bauxite under Coal Seams

by Shuai Li, Rui Zhang, Ru Feng, Boyi Hu, Guojun Wang and Haoxuan Yu

Minerals 2021, 11(7), 722; https://doi.org/10.3390/min11070722 - 05 Jul 2021

Cited by 16 | Viewed by 2449

Abstract

The mining of layered soft bauxite under coal seams (BCS) will cause serious underground goaf disasters and surface Bayer process red mud (BRM) pollution. In order to realize the safe and efficient mining of BCS, the feasibility of recycling BRM as a backfilling [...] Read more.

The mining of layered soft bauxite under coal seams (BCS) will cause serious underground goaf disasters and surface Bayer process red mud (BRM) pollution. In order to realize the safe and efficient mining of BCS, the feasibility of recycling BRM as a backfilling aggregate was explored. A series of tests were conducted to prevent the pollution diversion of BRM from surface storage to underground goafs, and a numerical simulation analysis of the backfilling mining process was carried out based on FLAC^3D to protect the overlying coal seam. The results show that: under the action of encapsulation, solidification and inhibiting precipitation from cementitious materials, the leaching concentration of harmful substances in red mud-based cemented backfill (RCB) can be reduced 70% more than fresh BRM. Mining disturbance redistributes the in-situ stress field of overlying strata; normal backfilling can not only reduce the pressure stress of pillars, but also release the tensile stress in the roof and floor from +0.4956 MPa to −0.1992 MPa, effectively preventing roof subsidence. Since the creep damage process of past backfill will absorb and dissipate lots of energy, the disturbance range caused by backfill mining is controlled within 3 m, which is only 10% of the open-stope method. Full article

(This article belongs to the Special Issue Backfilling Materials for Underground Mining, Volume II)

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11 pages, 2505 KiB

Open AccessArticle

Rheological Properties of Ultra-Fine Tailings Cemented Paste Backfill under Ultrasonic Wave Action

by Weicheng Ren, Rugao Gao, Youzhi Zhang and Maoxin Hou

Minerals 2021, 11(7), 718; https://doi.org/10.3390/min11070718 - 03 Jul 2021

Cited by 7 | Viewed by 1776

Abstract

Ultra-fine tailings cemented paste backfill (UCPB) exhibits special rheological characteristics with the effect of an ultrasonic sound field. In this study, in order to explore the thickening effect of slurry under ultrasonic wave action, we examined the rheological properties with ultrasonic wave tests [...] Read more.

Ultra-fine tailings cemented paste backfill (UCPB) exhibits special rheological characteristics with the effect of an ultrasonic sound field. In this study, in order to explore the thickening effect of slurry under ultrasonic wave action, we examined the rheological properties with ultrasonic wave tests of UCPB and the rheological properties after ultrasonic wave tests of UCPB. We found that the rheological curve of the slurry changed; the Herschel–Bulkley (HB) model in the initial state transformed into the Bingham model under the action of ultrasound. Ultrasonic waves have a positive effect on reducing slurry viscosity and yield stress. The rheological test of the slurry with ultrasonic wave action had a positive effect on significantly reducing the apparent viscosity and initial yield stress of slurry with a 62% mass concentration. The rheological test of slurry with ultrasonic wave action and the rheological test after ultrasonic wave action both have positive effects on reducing the viscosity and yield stress of the slurry with a 64% to 68% mass concentration; the overall effect of reducing the viscosity and yield stress of UCPB is greater after ultrasonic wave action of UCPB. Full article

(This article belongs to the Special Issue Backfilling Materials for Underground Mining, Volume II)

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16 pages, 4762 KiB

Open AccessArticle

Investigation on Mechanical Characteristics and Microstructure of Cemented Whole Tailings Backfill

by Armelle Estelle Belibi Tana, Shenghua Yin and Leiming Wang

Minerals 2021, 11(6), 592; https://doi.org/10.3390/min11060592 - 31 May 2021

Cited by 14 | Viewed by 2283

Abstract

A paste backfill performance can be primarily evaluated through the mechanical and physical characteristics of the components involved. In this study, the effects of solid components’ tailings, binders and waters contents on microstructural evolution and mechanical properties of uncemented whole tailings backfill (CWTB) [...] Read more.

A paste backfill performance can be primarily evaluated through the mechanical and physical characteristics of the components involved. In this study, the effects of solid components’ tailings, binders and waters contents on microstructural evolution and mechanical properties of uncemented whole tailings backfill (CWTB) mixtures were investigated. Different mixtures of ordinary Portland cement of 1, 3 and 5 wt. % and solid concentrations at 72 wt. %, 74 wt. % and 75 wt. % were selected and rheological test was conducted to define the slump fluidity and yield stress. The microstructure of the solid component before and after the preparation and chemical composition were analyzed by the Scanning electron microscope and XRD analysis, respectively. The results show that a positive correlation between yield stress and slump values of CWTB paste slurries, the decrease of flow consistence leads to the reduction of the water content on the CWTB mixtures and the flow resistance of the paste. With the highest solids content, unconfined compressive strength (UCS) of CWTB varies between 0.1–0.9 MPa. Increasing the solid content affects the porosity and improves the strength resistance of CWTB mixtures. The findings in this study can therefore lead us to a statement that CWTB chemical components seem to be an important factor in cemented paste backfill (CPB) design and mine operations. Full article

(This article belongs to the Special Issue Backfilling Materials for Underground Mining, Volume II)

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21 pages, 6822 KiB

Open AccessArticle

Experimental Study on the Mechanical Properties and Failure Characteristics of Layered Aeolian Sand Paste-Like Backfill—A Case Study from Shanghe Coal Mine

by Xiaoping Shao, Wuliang Sun, Xin Li, Long Wang, Zhiyu Fang, Bingchao Zhao, Jianpeng Sun, Chuang Tian and Baowa Xu

Minerals 2021, 11(6), 577; https://doi.org/10.3390/min11060577 - 28 May 2021

Cited by 9 | Viewed by 2151

Abstract

Filling mining is an important direction in green coal mining. In the filling site, a layered filling body can be formed due to technological problems. In this paper, we take Shanghe Coal Mine (Shaanxi Province, China) as the background. In order to explore [...] Read more.

Filling mining is an important direction in green coal mining. In the filling site, a layered filling body can be formed due to technological problems. In this paper, we take Shanghe Coal Mine (Shaanxi Province, China) as the background. In order to explore the mechanical properties and failure modes of layered backfill, specimens with different layered proportions (1:1, 1:3, 3:1) were made and studied concerning the aspects of wave velocity, porosity, strength and failure modes. The experimental result demonstrates that with the increase of curing time and fly ash (FA) content, the porosity of ASPLB decreases, the wave velocity and the strength increases. In addition, the layered structure has a significant effect on the strength and failure mode of the specimen. Uniaxial compression experiments showed that after 28 days of curing with Ratio III, the strength of layered backfill (LB) was reduced by 14% and the strength of 3:1 LB was increased by 16.7% and 40% compared with 1:1 LB and 1:3 LB, respectively. A digital speckle experiment showed that the failure mode of ASPLB is a vertical fracture without penetration, and the fracture propagation of layered ASPLB is hindered by the stratification. Based on the above research, the scheme that meets the requirements of the Shanghe Coal Mine is determined, and its reliability is verified, providing guidance for scientific stratification and the filling of gob. Full article

(This article belongs to the Special Issue Backfilling Materials for Underground Mining, Volume II)

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13 pages, 15691 KiB

Open AccessEditor’s ChoiceArticle

Investigation on Dynamical Mechanics, Energy Dissipation, and Microstructural Characteristics of Cemented Tailings Backfill under SHPB Tests

by Di Zheng, Weidong Song, Shuai Cao, Jiajian Li and Lijuan Sun

Minerals 2021, 11(5), 542; https://doi.org/10.3390/min11050542 - 19 May 2021

Cited by 17 | Viewed by 2246

Abstract

As mining depth increases, the backfill mining method is more and more widely used in underground mines. The dynamic load generated by the blasting can affect the stability of the cemented tailings backfill (CTB). The CTB samples were prepared to conduct a test [...] Read more.

As mining depth increases, the backfill mining method is more and more widely used in underground mines. The dynamic load generated by the blasting can affect the stability of the cemented tailings backfill (CTB). The CTB samples were prepared to conduct a test of the split Hopkinson pressure bar (SHPB) to investigate the dynamic disturbance of CTB. The present paper discusses dynamical mechanics, energy dissipation, and microstructure analysis of CTB. Micro-computer tomography (micro-CT) scanning of CTB samples after the SHPB test was performed to analyze the evolution of internal cracks. The experimental results showed that when the average strain rate (ASR) increased from 30 to 98 s⁻¹, the dynamic uniaxial compression strength (DUCS) of the CTB showed a trend of first increasing and decreasing with the increase in ASR. The dynamic stress–strain pre-peak curve of CTB directly enters the linear elastic stage. As ASR increases, the absorbed energy of the CTB shows a trend of first increasing and then decreasing. Moreover, according to the micro-CT scanning results, the crack area of CTB accounts for about 16% of the sample near the incident bar and about 1% near the transmitted bar. The crack area ratio is exponentially related to the specimen height. These findings can provide reasonable dynamical CTB strength data selection for underground pillar mining. Full article

(This article belongs to the Special Issue Backfilling Materials for Underground Mining, Volume II)

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14 pages, 2326 KiB

Open AccessArticle

Effect of Gypsum Addition on the Mechanical and Microstructural Performance of Sulphide-Rich Cemented Paste Backfill

by Yu Tang, Juanrong Zheng, Lijie Guo and Yue Zhao

Minerals 2021, 11(3), 283; https://doi.org/10.3390/min11030283 - 09 Mar 2021

Cited by 12 | Viewed by 1796

Abstract

The present study investigates the effect of β-hemihydrate gypsum (HG) dosages on the mechanical and microstructural performance of cemented paste backfill (CPB) produced from sulphide-rich mine tailings using NaOH-activated slag (NAS) as the major binder. X-ray diffraction (XRD), scanning electron microscopy (SEM) and [...] Read more.

The present study investigates the effect of β-hemihydrate gypsum (HG) dosages on the mechanical and microstructural performance of cemented paste backfill (CPB) produced from sulphide-rich mine tailings using NaOH-activated slag (NAS) as the major binder. X-ray diffraction (XRD), scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) analyses were carried out to elucidate the mineralogical composition and microstructure of NAS-HG-CPB samples. The results illustrate that the main hydration products of NAS-HG-CPB from sulphide-rich tailings are crystalline (CaSO₄•2H₂O and ettringite (AFt), 3CaO•Al₂O₃•3CaSO₄•32H₂O) and amorphous. The results also show that the 28 d unconfined compressive strength (UCS) of CPB with 30 wt. % HG replacing NAS increased by 52% compared to the UCS of CPB containing no HG, and both have stable long-stage (180 d) UCS (i.e., no strength loss). Excess HG addition (≧50 wt. %) reduced the early-stage (≦28 d) UCS of NAS-HG-CPB and led to unstable long-stage (180 d) UCS by the formation of secondary gypsum. The use of 30 wt. % HG replacing NAS in NAS-HG-CPB accelerates the hydration process of ground granulated blast furnace slag (GGBS) in the alkaline solution by forming ettringite (AFt), leading to the denser microstructure and improved mechanical performance in comparison with CPB containing no HG. The NAS-HG binder with low dosages of HG (≦30 wt. %) will be a promising binder for stabilising sulphide and non-sulphide tailings and CPB production. Full article

(This article belongs to the Special Issue Backfilling Materials for Underground Mining, Volume II)

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