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Backfilling Materials for Underground Mining, Volume III

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A special issue of Minerals (ISSN 2075-163X). This special issue belongs to the section "Mineral Processing and Extractive Metallurgy".

Deadline for manuscript submissions: closed (20 January 2024) | Viewed by 16270

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Dr. Abbas Taheri

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Chair in Mine Design, The Robert M. Buchan Department of Mining, Queen’s University, Kingston, ON K7L 3N6, Canada
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
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Dear Colleagues,

Backfilling of mined-out areas is a fundamental component of many underground mining operations. The backfill material supports the surrounding rock mass, reduces wasteful dilution, enables a safe working area for production activities, and mitigates surface subsidence risk. Combining tailing materials in the backfill makes it possible to reduce a mine's environmental footprint and assists with the final site rehabilitation. Therefore, cemented paste backfill (CPB) has become an essential component of underground mining operations. CPB is a mixture of tailings, water, and cement used to fill underground stopes. Reducing the backfilling cost by decreasing the cement content may increase ore dilution from poorly performing backfill exposures. Alternatively, increasing the cement content will raise the costs, though it could increase productivity through improved mining system cycle times. The use of other binder materials can reduce the costs, while maintaining optimal strength performance of the backfilling. Moreover, tailings’ particle size and density significantly alter the strength, microstructure, water demand, and economic costs of backfill mixtures. Besides CPB, solid waste backfilling has become popular in underground mining activities, especially coal mining. In many mining projects with cement paste backfill (CPB), backfill samples retrieved from the underground mine show higher strength properties than those prepared in the laboratory. Previous studies demonstrated that the properties of CPB are also dependent on placement condition during curing. In coal mining, backfilling of the gob area is performed in conjunction with the mining operations. The properties of solid-waste backfilled materials may significantly influence local strata behavior. This Special Issue aims to bring together studies from all these areas, including experimental studies, constitutive model developments, analytical and numerical analyses, to characterize backfill materials. We welcome studies on mine stability and operation issues in mining with backfill, as well as backfill mining case studies.

Dr. Abbas Taheri
Guest Editor

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Keywords

cement paste backfilling
solid backfilling
underground mining
constitutive models
numerical modelling
experimental studies
green mining

Related Special Issues

Backfilling Materials for Underground Mining in Minerals (23 articles)
Backfilling Materials for Underground Mining, Volume II in Minerals (21 articles)

Published Papers (13 papers)

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Research

26 pages, 19174 KiB

Open AccessArticle

Mechanical Characteristics and Macro–Microscopic Response Mechanisms of Cemented Paste Backfill under Different Curing Temperatures

by Chao Zhang, Abbas Taheri, Cuifeng Du, Wenhao Xia and Yuye Tan

Minerals 2024, 14(4), 433; https://doi.org/10.3390/min14040433 - 22 Apr 2024

Viewed by 288

Abstract

Macroscopic and microscopic properties of cemented paste backfill (CPB) were studied through uniaxial compressive testing, acoustic emission (AE) monitoring, and microscopic feature analysis. The research shows that the uniaxial compressive strength (UCS) and elastic modulus have an exponential function type positive correlation with the increase in curing time and a polynomial function type with the rise of curing temperature; the mechanical parameters reach the maximum when the curing temperature is 40 °C. Increasing the curing time and curing temperature can promote the transition from shear crack to tensile crack. Increasing the curing time and raising the curing temperature both promote the transition of shear crack to tensile crack in the CPB. Overall, the crack mode is a combination of tensile and shear crack. At room temperature, the shear cracks dominates in the initial stage, but the proportion of the shear cracks decreases as the pressure increases in uniaxial compression test. At a curing temperature of 60 °C, the crack mode transitions to a tensile-shear mixed crack, with tension becoming the dominant crack mode. Microscopic analysis suggests an excellent linear correlation between the pore fractal dimension, UCS, and elastic modulus. When the pore fractal dimension decreases, the mechanical parameters also decrease. The pore fractal dimension can effectively characterize the macroscopic mechanical properties. Finally, the curing temperature is divided into two stages, with 40 °C as the dividing line for analysis. In the first stage, the increase in curing temperature effectively improved the mechanical parameters; in the second stage, the excessively high hydration reaction rate weakened the mechanical parameters. Full article

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

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18 pages, 3918 KiB

Open AccessArticle

Additivity Effect on Properties of Cemented Ultra-Fine Tailings Backfill Containing Sodium Silicate and Calcium Chloride

by Bingwen Wang, Su Gan, Lei Yang, Zhongqi Zhao, Zhao Wei and Jiachen Wang

Minerals 2024, 14(2), 154; https://doi.org/10.3390/min14020154 - 31 Jan 2024

Viewed by 793

Abstract

Tailings from gold mines gradually approach ultra-fine, making mine backfill costs higher and strength lower, which poses a serious threat to the safety of underground personnel and equipment. It is well known that suitable chemical admixtures can enhance the working properties of mortar materials. Therefore, in order to achieve the purpose of reducing the cost of ultra-fine tailings backfill and improving the working performance of ultra-fine tailings filling slurry, this paper provides a study on the effect of sodium silicate and calcium chloride on the properties of ultra-fine tailings cemented backfill materials. The results of experimental studies through rheology, strength, and microstructural tests, etc., showed that the optimal proportioning parameters of cementitious materials are 76.92% blast furnace slag, 19.24% carbide slag, and admixtures of 2.88% sodium silicate and 0.96% calcium chloride. The 3, 7, and 28-day uniaxial compressive strength of the ultra-fine tailings cemented paste backfill with the newly formulated blast furnace slag-based cementitious material increased by 124%, 142%, and 14%, respectively, compared to that of the ultra-fine tailings cemented paste backfill with the P. O42.5 cement. The setting time for ultra-fine tailings cemented backfill slurry is shortened by the addition of admixtures, and the shear stress of the slurry is correlated with the amount of hydration product generation and its formation of flocculating structure. Moreover, the cost of the newly prepared cementitious material is much lower than that of traditional cement, which lays a good foundation for the cemented filling of ultra-fine tailings. Full article

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

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21 pages, 11474 KiB

Open AccessArticle

Study on Aeolian Sand-Box Backfill Geomechanical Characteristics and Overlying Strata Control Effects

by Bo Zhao, Zhiyi Zhang, Xiaoping Gong, Wei Wang, Xiaoyong Tong, Hui Chen, Weiming Guan, Xin Li, Shuo Feng, Dezhi Yang, Lubo Huang and Yuhang Zhao

Minerals 2023, 13(12), 1556; https://doi.org/10.3390/min13121556 - 18 Dec 2023

Viewed by 922

Abstract

The aeolian sand-box backfilling method proves effective for environmentally friendly coal extraction in northwestern regions, including Xinjiang. This study investigated the geomechanical characteristics of aeolian sand-box backfill material and its control effects on overlying strata through indoor experiments, mechanical analysis, and numerical simulations. Uniaxial compression tests on models with varying mesh sizes, wire diameters, and dimensions revealed that larger mesh sizes and wire diameters increased the bearing capacity of the aeolian sand-box backfill material, while increasing dimensions had the opposite effect. A mechanical analysis of the metal mesh box deformation produced equations describing its restraining force. Subsequent experiments and simulations on models of different dimensions consistently demonstrated the material’s mechanical properties, with stress-displacement curves closely aligned. 3DEC5.2 software simulations highlighted the effectiveness of aeolian sand-box backfill material in controlling displacement and stress variations in goaf areas. Notably, smaller-sized backfill material exhibited a more pronounced impact on controlling overlying strata displacement and stress development. Full article

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

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14 pages, 2885 KiB

Open AccessArticle

Impact of Admixtures on Environmental Footprint, Rheological and Mechanical Properties of LC₃ Cemented Paste Backfill Systems

by Sébastien Dhers, Rebecca Guggenberger, Dominik Freimut, Shirin Fataei, Peter Schwesig and Zlatko Martic

Minerals 2023, 13(12), 1552; https://doi.org/10.3390/min13121552 - 16 Dec 2023

Viewed by 894

Abstract

This study investigates the time-dependent rheological behavior of cemented paste backfill (CPB) that contains calcined clay as a binder, particularly with LC³ (Limestone Calcined Clay Cement) compositions, using two different PCEs (Polycarboxylate Ether) superplasticizers. Rheological measurements have been conducted on four different mix designs using the Bingham model to describe the CPB mixtures. Both yield stress and plastic viscosity have been reported, and the impact of the admixture on these parameters has been investigated. Unconfined compressive strength (UCS) was measured over 182 days for all mix designs. Both admixtures showed better workability in all cases, with significantly improved yield stress and plastic viscosity compared to the reference, while showing little to no negative impact on strength over time. This study highlights that both from a binder and an admixture point of view, relevant to the industry, these calcined clay systems are ready to be used in a CPB and could make a significant impact on the sustainability of a mining operation in the near future. Full article

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

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17 pages, 4224 KiB

Open AccessArticle

Experimental Investigation into the Proportion of Cemented Aeolian Sand-Coal Gangue-Fly Ash Backfill on Mechanical and Rheological Properties

by Zhijun Zheng, Baogui Yang, Chengjin Gu, Faguang Yang and Hao Liu

Minerals 2023, 13(11), 1436; https://doi.org/10.3390/min13111436 - 13 Nov 2023

Cited by 1 | Viewed by 851

Abstract

Aiming at the problems of large water secretion, poor suspensibility and low strength of cemented aeolian sand (AS)-fly ash (FA) backfill (CAFB) mixtures, CAFB was doped with fine coal gangue (CG) particles crushed to less than 4 mm and configured as cemented aeolian sand-coal gangue-fly ash backfill (CACFB) mixtures, in which coal gangue accounted for 8% of the mass ratio of the slurry. Through UCS and rheological experiments, using the response surface methodology and an orthogonal design, the following conclusions were drawn: (1) With the increase in ordinary Portland cement (PO) and slurry concentration, the UCS of the CACFB increased. (2) With the increase in the FA dosage, the UCS of the CACFB decreased first and then increased due to the gradual increase in FA dosage, destroying the reasonable ratio of the material and leading to the reduction in the material’s UCS, and with the growth in time, the volcanic ash effect of the FA caused the UCS of the material to increase. (3) With the increases in slurry concentration, the yield stress and viscosity coefficient of the slurry increased. (4) Reasonable proportions for CACFB should ensure the strength characteristics and rheological properties of the material. Through theoretical and experimental research, the final reasonable proportions were as follows: the concentrations of slurry, AS, CG, FA and PO were 77.5%, 42%, 8%, 17.5% and 10%, respectively. This ensured that the UCSs of the CACFB at 3 d, 7 d and 28 d were 1.2 MPa, 2.5 MPa and 4.3 MPa, respectively; the yield stress of the CACFB was 495 Pa, and the viscosity coefficient was 3.97 Pa·s. These reasonable proportions of the CACFB can meet the strength index and flow property of material industrial experiments. Full article

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

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15 pages, 16310 KiB

Open AccessArticle

The Mechanism of Viscosity-Enhancing Admixture in Backfill Slurry and the Evolution of Its Rheological Properties

by Liuhua Yang, Hengwei Jia, Huazhe Jiao, Mengmeng Dong and Tongyi Yang

Minerals 2023, 13(8), 1045; https://doi.org/10.3390/min13081045 - 06 Aug 2023

Cited by 8 | Viewed by 1048

Abstract

Since filling slurry is a cement-based material, viscosity-enhancing admixture exerts a significant effect on its rheological performance and mechanical properties. Viscosity-enhancing admixture can improve pipeline transportation performance and reduce pipeline wear during the filling process of a kilometer-deep mine by changing the plastic viscosity and yield stress of high-concentration filling slurries. In order to reveal the influence mechanism of viscosity-enhancing admixture on rheological performance in slurry, the influence of viscosity-enhancing admixture on the rheological performance of slurry is explored by adjusting viscosity-enhancing admixture dosage and conducting bleeding test, liquidity test, and rheological performance test. The extended DLVO theory is employed to analyze the mechanism of HPMC on the stability of filling slurry. The results show that compared with ordinary slurry, after adding HPMC and XG, the particles of filling slurry are prone to link to form a mesh structure. Besides, the increasing frictional force between particles results in a significant decrease in the bleeding rate and liquidity of the slurry. Such an effect becomes more obvious with the increase of viscosity-enhancing admixture dosage. Meanwhile, the overall effect of HPMC molecules is better than that of XG molecules since HPMC can reduce inter-particle repulsion and facilitate particle aggregation. The optimal dosage is about 0.1%, at which time the yield stress of the filling slurry increases from 89.236 to 160.06 Pa, the plastic viscosity increases from 0.296 to 1.063 Pa·s, and the compressive strength increases from 2.58 to 3.59 MPa in 28 days. The study reveals the influence of viscosity-enhancing admixture on the rheological performance of filling slurry and its evolution characteristics, which provides theoretical support for the development of filling resistance and wear reduction technology. Full article

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

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16 pages, 7261 KiB

Open AccessArticle

Study on the Pb²⁺ Consolidation Mechanism of Gangue-Based Cemented Backfill

by Hao Wang, Qi Wang, Yuxin Hao, Yingying Wang, Burui Ta and Jian Meng

Minerals 2023, 13(3), 354; https://doi.org/10.3390/min13030354 - 02 Mar 2023

Cited by 1 | Viewed by 1265

Abstract

Coal mining produces a large amount of gangue that pollutes the environment, causing surface subsidence and damaging the groundwater systems. Backfill mining is an effective technology used to solve this problem, but there is a risk of polluting the groundwater due to the heavy metal ions present in the backfill material. Pb²⁺ has been determined to be a representative element because of its existence in coal gangue samples but not in fly ash. The risk of gangue-based cemented backfill causing groundwater pollution can be evaluated by studying the Pb²⁺ leaching from gangue under various conditions. When comparing the leaching amounts of Pb²⁺ from the coal gangue particles and the test blocks, it was found that cement filling has an obvious consolidation effect on the Pb²⁺ in coal gangue. The above process shows that cemented backfill has an obvious consolidation effect on the Pb²⁺ in gangue. The results of the theoretical analysis, X-ray, and SEM show that the consolidation mechanism can be divided into four modes: physical encapsulation, ion exchange, ion adsorption, and chemical reaction. The results are of great significance for revealing the leaching mechanism of the heavy metals in coal gangue, assessing the risk of heavy metal pollution in groundwater via gangue-cemented backfill, and improving the mining theory of the gangue-cemented filling and groundwater protection. Full article

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

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16 pages, 11387 KiB

Open AccessArticle

Effect of Content and Length of Polypropylene Fibers on Strength and Microstructure of Cementitious Tailings-Waste Rock Fill

by Bo Gao, Shuai Cao and Erol Yilmaz

Minerals 2023, 13(2), 142; https://doi.org/10.3390/min13020142 - 18 Jan 2023

Cited by 10 | Viewed by 1287

Abstract

The mechanical strength properties of cemented tailings backfill are very important for the safe and environmentally friendly mining of mineral resources. To check the impact of polypropylene fiber on strength and microstructure of cementitious tailings waste rock fill (CTWRF), diverse fiber lengths (6 and 12 mm) and dosages (0-control specimen, 0.3, 0.6, and 0.9 wt.%) were considered to prepare fiber-reinforced CTWRF (FRCTWRF) matrices. Experiments such as UCS (uniaxial compressive strength), X-ray CT (computed tomography), and SEM (scanning electron microscopy) were implemented to better characterize the backfills studied. Results showed that UCS performance of FRCTWRF was the highest (0.93 MPa) value at 6 mm fiber long and 0.6 wt.% fiber content. The peak strain of FRCTWRF was the highest (2.88%) at 12 mm fiber long and 0.3 wt.% fiber content. Growing the length of fiber within FRCTWRF can reduce its fracture volume, enhancing the crack resistance of FRCTWRF. Fiber and FRCTWRF are closely linked to each other by the products of cement hydration. The findings of this work will offer the efficient use of FRCTWRF in mining practice, presenting diverse perspectives for mine operators and owners, since this newly formed cementitious fill quickens the strengths required for stope backfilling. Full article

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

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16 pages, 18296 KiB

Open AccessArticle

Measuring Ultrasonic and Electrical Properties of Early-Age Cemented Tailings Backfill

by Weilv Wu, Wenbin Xu and Yalun Zhang

Minerals 2023, 13(2), 135; https://doi.org/10.3390/min13020135 - 17 Jan 2023

Cited by 1 | Viewed by 953

Abstract

The setting behavior strongly affects the workability and loading capacity of a fresh cemented tailings backfill (CTB). The Vicat test is a conventional way to measure the setting time of a fresh cementitious mixture, using a standard needle to detect penetration resistance. However, this method is limited to laboratory testing, it is difficult to carry out in underground closed stopes. In this study, two nondestructive methods, the ultrasonic pulse and electrical conductivity tests, contrasting two traditional methods, hydration heat measurement and the Vicat test, are used to illustrate the setting process of early-age CTB. The effect of cement content (e.g., 2.5%, 5% and 7.5%) and tailings type (silica tailings and iron mine tailings) on the hydration heat of early-age CTB are recorded as well. The results show that, as the CTBs change from solid–liquid mixtures to solids, the ultrasonic pulse frequency converts from low to high and the electrical conductivity turns from growth to decline. As the degree of hydration increases, the solid connections continuously increase, which increases the ultrasonic amplitude rapidly and decreases electrical conductivity. The TG value can be effectively used to predict the initial set time of cemented silica tailings backfill. For cemented iron tailings backfill, although the solid phase ultrasonic path is formed, more hydration products are needed to reach the specific shear stiffness, meaning the initial set lags behind the change in ultrasonic frequency signal. Full article

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

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22 pages, 46151 KiB

Open AccessArticle

Numerical Study on the Vibratory Compaction Mechanism of the Sand-Gabion Backfills in Underground Coal Mines

by Zhiyi Zhang, Wei Wang and Bo Zhao

Minerals 2022, 12(11), 1428; https://doi.org/10.3390/min12111428 - 10 Nov 2022

Cited by 2 | Viewed by 1303

Abstract

Coal mine backfilling can effectively prevent large-scale movement of rock formations, not only improving the overall production capacity of the mine but also protecting the surface from destruction and maintaining the original ecological environment. Backfilling extent and backfills compactness are two factors determining the supporting effect on the overburdens in underground coal mines. To make full use of the aeolian sand as the backfill materials in underground coal mines in the desertification areas, Northwest China. Then, vibratory compaction was proposed to enlarge the compactness of these sand-gabion backfills by considering the limited working space. After that, the movement law of the sand particles during vibratory compaction, the influencing law of the vibratory parameters, and the gabion constraint on the ultimate compactness of the sand-gabion backfills were studied using the discrete element software PFC3D from the microscopic point of view. It was found that the aeolian sand particles are more likely to inter-squeeze under vibration than under static load. Furthermore, there are a series of optimal vibratory compaction parameters to the inner aeolian sand for each external gabion constraint strength. The optimal vibration parameters were frequency 50 HZ, excitation force 0.3 MPa, amplitude 40 KPa, and vibration time 4 s. Conclusions of this study can provide references for enlarging the compactness of the sand-gabion backfills in the underground goaf in the desertification area of Northwest China. Full article

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

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12 pages, 3100 KiB

Open AccessArticle

A Green Sintering-Free Binder Material with High-Volumetric Steel Slag Dosage for Mine Backfill

by Bolin Xiao, Huatao Huang and Jingyu Zhang

Minerals 2022, 12(8), 1036; https://doi.org/10.3390/min12081036 - 18 Aug 2022

Cited by 3 | Viewed by 1360

Abstract

Cemented paste backfill (CPB) is a sustainable mining method that has been increasingly utilized. Demand for high-performance and low-cost binder material is one of the limitations in CPB utilization. This work aims to examine a new, green, and economical steel-slag-based binder for CPB and to explore valorization techniques of steel slag (SS). Proportioning experiments were performed to obtain the best binder recipes for various steel slag dosages. The hydration heat, hydration products, and pore structure of a high-volumetric steel slag binder (H-SSB) were further inspected. Results show that the H-SSB, which contains 50 wt.% of SS, has a competitive strength performance superior to ordinary Portland cement (OPC) regardless of its 30–50% lower cost than OPC. The 7-day and 28-day strengths of H-SSB CPB are 1.24 and 0.74 MPa, respectively, which meets the meets of most free-standing backfill applications. The H-SSB generates less hydration heat and a larger amount of gel and ettringite hydrates than OPC in its early hydration, which can reduce the thermal expansion risks and strengthen the mechanical properties of CPB. Though the H-SSB CPB has a larger porosity than OPC-CPB at 28-day curing (45% vs. 37%), most pores are small and uniform in diameter (500–2000 nm), which is less harmful to CPB strength development. The H-SSB has secondary hydration effects in the long-term age, which can fill and refine the pore structure. The proposed H-SSB has benefits in reducing backfill costs, minimizing green gas emissions, and extending steel slag valorization techniques that can promote sustainable development of the mining and steel industries. Full article

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

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16 pages, 6251 KiB

Open AccessArticle

Expansion Properties of Cemented Foam Backfill Utilizing Coal Gangue and Fly Ash

by Xiao Wang, Jixiong Zhang, Meng Li, Feng Gao, Abbas Taheri, Binbin Huo and Ling Jin

Minerals 2022, 12(6), 763; https://doi.org/10.3390/min12060763 - 15 Jun 2022

Cited by 12 | Viewed by 1840

Abstract

The cemented backfill (CB) utilizing coal gangue (CG) and fly ash (FA) is widely applied in coal mines. However, the bleeding and shrinkage of CB leads to insufficient contact with surrounding rock, which is not beneficial for controlling roof subsidence and even stope stability. Herein, a cemented foam backfill (CFB) formulation is demonstrated, employing hydrogen dioxide (H₂O₂) as a chemical foaming agent. The cement and FA show noticeable inhibiting effects on volume expansion due to the network formed by their hydrates. Moderately lower cement, FA, and solid concentration are beneficial to improve volume increment and prolong expanding duration. A foaming coefficient (k) is proposed in theory to evaluate the foaming efficiency. The k_em values, determined by volume evolution experiments of CFB slurries, provide a calculation basis for the needed dosage of H₂O₂ solution targeting specific volume increment. CFB specimens with expanding ratios of 21%~103% and densities of 994~592 kg/cm³ were prepared, with an actual foaming coefficient of 52.40 cm³/g and uniaxial compressive strength (UCS) of 0.32~0.55 MPa. The mass of H₂O₂ solution was 1.9%~11.3% of cement and 0.29%~1.67% of total solid materials by weight. The UCS decline compared to CB was attributed to rich pores observed by CT and carbonation indicated by X-ray diffraction (XRD). Full article

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

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19 pages, 8319 KiB

Open AccessArticle

Evolution Characteristics of Overlying Strata Fractures in Paste Composite Filling Stope

by Wenyu Lv, Kai Guo, Haijin Wang, Kun Feng and Dongdong Jia

Minerals 2022, 12(5), 654; https://doi.org/10.3390/min12050654 - 22 May 2022

Cited by 7 | Viewed by 1666

Abstract

Paste composite filling mining (PCFM) is one of the effective ways to achieve water-preserved mining (preservation of the waterproof strata). To investigate the laws of fracture propagation of the overlying strata in the PCFM stope, a kinematic model of overlying strata in the PCFM was established, which identified the major determinants to the development of overlying strata fractures. Taking the 112,201 working face of the test mine as the research background, the physical similar simulation, numerical computation, and theoretical analysis were combined to analyze the development characteristics of overlying strata fractures in the PCFM under the reaction between many factors (mining height, filling ratio, burial depth). The results show that the larger the mining height of the working face, the larger the development degree of overlying strata fractures. When the mining height is smaller, fractures are mostly distributed on both sides of the coal wall; when the mining height is larger, overlying strata fractures are mostly distributed on both sides of the coal wall and the upper part of overlying strata. The larger the paste filling ratio of the working face, the smaller the development degree of overlying strata fractures. Overlying strata fractures are mostly distributed in overlying strata on both sides of the coal wall. When the filling ratio of the working face increases, it is possible to effectively control the development of overlying strata fractures. The shallower the burial depth of the working face is, the faster the fractures are developed. With the increase of the burial depth, the development of overlying strata fractures is reduced, and overlying strata fractures will finally tend to be a stable value. The research results provide an important theoretical foundation for the application of the localized paste filling mining technique in the water-preserved mining, and also complement the theories of filling mining. Full article

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

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