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shows a top view of the FLAC3D model for simulating the physical model test S1A (see details in Table 1) with two vertical monitoring lines: Line 1 and Line 2. Fig. 5 shows the variation of the total displacement (Fig. 5a), XXhorizontal stress (Fig. 5b), YY-horizontal stress (Fig. 5c), and ZZvertical stress (Fig. 5d) with different backfilling steps along Line 1 at different depth h before the removal of the front confining wall. It can be seen that the numerical results tend to become stable when the number of filling layers reaches to 18. Hence, the filling of the physical models will hereafter be simulated with 18 layers. Fig. 6 shows the variation of the total displacement (Fig. 6a) and factor of safety (Fig. 6b) of the exposed backfill at an exposed height of H f = 1.4 m along Line 2 with different excavating steps. It can be seen that the number of excavation layers has few influence on the numerical results. Therefore, the physical model tests will be simulated with a backfilling of 18 layers and an excavation of the front wall in one step.
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![Fig. 1. Wedge block model proposed by Mitchell et al. [17].](profile/Guangsheng-Liu-4/publication/308579303/figure/fig1/AS:622099337064455@1525331448241/Wedge-block-model-proposed-by-Mitchell-et-al-17_Q320.jpg)
![Fig. 3. Schematic view of a physical model of Mitchell et al. [17] (a);...](profile/Guangsheng-Liu-4/publication/308579303/figure/fig3/AS:622099337060357@1525331448298/Schematic-view-of-a-physical-model-of-Mitchell-et-al-17-a-numerical-model-of-the_Q320.jpg)
Mitchell?s solution is commonly used to determine the required strength of vertically exposed cemented backfill in mines. Developed for drained backfill, Mitchell model assumed a zero friction angle for the backfill. Physical model tests were performed. Good agreements were obtained between the required strengths predicted by the analytical solutio...
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... In order to meet the ever-increasing demand for mineral resources consumption and supply, increasing mining production capacity is an important consideration for designers and managers of nonferrous underground mines, however, adequate safety and reasonable mining operation costs must be guaranteed. Currently, long-hole stage open stoping with subsequent backfill is the most efficient mining method and represents the development direction of large-scale underground mining in nonferrous metal mines [1][2][3]. ...
... In this mining method, a traditional bottom-up mining sequence is usually adopted, in which the ore body is vertically divided into a number of mining stages, as illustrated in Figure 1a, where the stopes (1, 3,5) in Stage-1 are excavated and then backfilled to provide a base platform for the mining of upper stopes (2,4,6) in Stage-2. Meanwhile, continuous stopes are divided along the horizontal direction of each stage, and the primary mary stopes (1, 2) are excavated preferentially and backfilled with cement to serve as artificial vertical pillars for the following excavations of secondary stopes (3,4,5,6), which are mostly backfilled without adding cement to save costs. ...
In the long-hole stage open stoping with subsequent backfill mining of underground metal mines, the selection or optimization of stope dimension parameters is significant for safe and economic mining operations. To analyze the optimal stope sizes, the Mathews empirical graph method and FLAC3D numerical method can be used, but the analyzed safety results of the two methods are generally independent from each other. More importantly, economic indicators including production capacity and mining costs should be considered simultaneously to optimize the stope dimension which was mostly ignored in previous reports. In this paper, a new CRITIC-GRA model was proposed for the first time to build up a multi-factor quantitative optimization for stope dimension, which allows for a comprehensive analysis with preset influential safety and economic indicators. The indicators considered include the safety indicators such as stability probability for the side walls and roof of the open stope via the updated Mathews graph method, maximum displacement, plastic zones volume and maximum principal stress via FLAC3D simulations, as well as economic indicators such as mining costs and stope production capacity in mine operations. The model was then illustrated in an underground iron mine. With the given rockmass quality in the mine, the overall stability of the open stope can be improved instead of reduced to enlarge the single stage stope height (60 m) to a double stage height (120 m) by reducing the stope width from 20 m to 15 m, thereby significantly increasing the mineable ore amount and improving the stope safety. An integrated evaluation of open stope stability, mining capacity and costs objectively determined that scheme No. 10, with a slope length of 50 m, a width of 15 m and a height of 120 m, was the optimum out of the 20 preset schemes. The new CRITIC-GRA model offers a dependable reference tool for determining the optimal stope dimensions in similar underground mines.
... The CTB pillar must remain stable during the mining of the adjacent secondary stope (Pengyu and Li 2015). Therefore, an estimate of the safety factor required of the exposed fill amidst the excavation of the adjacent stope is crucial, otherwise, the backfill would collapse and threaten the safety of the mine workers while also diluting the blasted ore (Li and Aubertin 2012;Liu et al. 2016;Porathur et al. 2022). Therefore, it is necessary to determine the required cohesion at failure or the minimum required cohesion with optimum cement content to ensure the stability of the CTB Mitchell et al. 1982). ...
... However, the MM solution, just like Mitchell et al.'s (1982), considered the friction angle between the backfill and sidewalls to be zero and neglected the shear strength (cohesion and friction angle) along the back wall (Li and Aubertin 2012;Liu et al. 2016). Neglecting the shear strength due to friction along the interface between the backfill and sidewall has also been deemed a too conservative approach (Li 2014a). ...
The stability analysis of the backfill support system has been a significant analysis of stope performance in stoping mining method. For the past decades, the strength of exposed backfill was preferred to be conducted using analytical solutions based on the limit equilibrium theory. Nevertheless, these solutions have neglected the effect of layering that is endured by the backfill in the large stope. These methods appear to provide unrealistic results in stratified backfill stopes. This study introduces a modified solution that considers the shearing force along the backfill layers interface. The proposed solution method confirms that when the effect of layering is included the solution differs from the existing limit equilibrium solutions. Various examples are provided to validate the proposed analytical solution method.
... Together with the validation of the simulated excess PWP u for back ll slurry, the effective stress distribution of the consolidating back ll is another key issue to be veri ed, because the stresses close to the bottom of the slurried back ll are proved to be a crucial factor affecting the stability of man-made barricade structures in access drives to stopes, and the stresses along the back ll height in stopes are signi cant for understanding the ground control behaviors of back ll and its strength requirement after side exposure in mining procedures (Liu et al. 2016a(Liu et al. , 2016b(Liu et al. , 2017(Liu et al. , 2018(Liu et al. , 2021. When the back ll is completely under water at the moment of the stope void being fully lled, which means the assumed phreatic surface is at the top of the back ll (i.e., H p =0), the effective vertical stress used as an analytical reference to validate the numerically simulated effective vertical stress of the slurried back ll at different accreting and consolidating times. ...
A reasonable assessment on pore water pressure (PWP) and effective stresses of backfill slurry during consolidation process is critical to ensure a secure and economic backfilling in mine stopes. This task can be accomplished by analytical or numerical simulations, but most of the previous simulations did not take into account the hydro-geotechnical properties of rockmass in adjacent stopes, which was mainly simplified to an impervious boundary. This treatment may not be representative of the field conditions in underground mine stopes because of the presence of geological joints and/or mining induced cracks in surrounding rockmass that serve as seepage paths for pore water discharged from the filled slurry. In this paper, numerical modeling was conducted with FLAC3D to investigate consolidation process of uncemented backfill slurry in a vertical stope considering the surrounding rockmass with different permeability, initial saturation, porosity, and the rockmass width. The results show that the PWP and effective stresses of backfill slurry in a mine stope considering adjacent rockmass can be very different with numerical outcomes by simplifying the rockmass as impermeable or permeable boundaries assumed in previous studies. For the same backfill slurry in mine stopes with different drainage conditions along side walls, the peaks of the PWP and effective stress differ by a factor of three to five for each consolidation process. This would make the evaluations on backfill slurry consolidation either too conservative, with impermeable side walls, or too aggressive, with free drainage side walls, ignoring the actual rockmass hydro-geotechnical parameters. Different hydro-geotechnical properties of the rockmass have different impacts on the evolutions of the PWP and effective stresses of the consolidating backfill slurry. However, when the hydraulic conductivity of the surrounding rockmass is lower than 10 − 8 m/s, the simulated PWP and effective stresses for the backfill slurry will be comparable to the numerical models that simplify the rockmass to a watertight boundary. Furthermore, the influences of different hydro-geotechnical properties of adjacent rockmass on the lateral earth pressure coefficient of consolidated backfill were also discussed. In addition to the validations of simulated PWP and stresses against the analytical results with Gibson model and an arching model respectively, the numerical results were compared with the previous published in-situ monitoring benchmarks to validate the consolidation process simulated by FLAC3D here.
... The overall pore space of CACFB is decreasing with the increase of the solid concentration of the material. As a result, the UCS of CACFB is increasing [24][25][26][27]. ...
This paper investigates that the influence of the independent variables of particle size of coal gangue (CG), concentration and coal gangue content on the UCS of cemented aeolian sand (AS)-coal gangue-fly ash (FA) backfill (CACFB) mixtures through the thermogravimetric, piezomercurial, microscopic experimental means by adding certain particle size of coal gangue particles in the cemented aeolian sand -fly ash backfill (CAFB) mixtures. Through the relevant experiments, the following conclusions are drawn: 1. with the increasing particle size of CG particles, the UCS of the CACFB is increasing in which the 7d UCS of R-C-1, R-C-2, R-C-3 and R-C-4 were 2.05 MPa, 2.11 MPa, 1.94 MPa and 2.09 MPa, respectively; 2. After 7 days of curing age, the UCS of CACFB is generally 1.5 MPa higher than that of CAFB.; 3. Because CG particles play a role in increasing slurry concentration, compactness and improving particle gradation in CACFB, the UCS of CACFB is much higher than the UCS of CAFB.; 4. The improvement UCS of CACFB will greatly improve the popularization and application of filling mining in northern Shaanxi mining area, and reduce the damage to environmental water resources and land resources in the mining area.
... Considering the additional parameters of shear strengths and a high aspect ratio (HAR; Height-H/Width-B), Li [21] recommended a comprehensive solution for predicting the strength of backfill. Later, Liu et al. [22], using physical and numerical modelling, suggested that the analytical solution developed by Mitchell et al. [18] is useful in estimating the required strength of a vertically exposed cemented backfill stope in the short term. However, it is invalid for assessing the stability (long-term) of exposed fully drained backfill. ...
... Although the analytical solutions form the basis of backfill strength design, these cannot predict the mechanism of failure. In that case, the numerical modelling technique serves the purpose of predicting the failure mechanism in addition to the required backfill strength [22]. A few of the previously reported literature on the strength design of backfill using numerical modelling are presented in Table 1 and explained hereafter. ...
... Further, Yang et al. [26] used FLAC3D for modelling a stage subsequent filling mining method with a stage stope dimension of approximately 100 m and obtained a relationship between the exposed backfill height and the required strength. Liu et al. [22] reproduced the physical model tests of Mitchell et al. [18] and used FLAC3D to analyse the total stress, strength design of backfill and short-term stability without considering pore water pressure. Yang et al. [23] demonstrated that the failure plane changes from planar to spoon-shaped with increasing cohesion. ...
... The hardened CTB can interact with the rock walls or pillars to form a common support system, resisting the deformation of the surrounding rock walls [11][12][13][14]. Fig. 1 shows the schematic diagram of the interaction between the CTB and the surrounding rock walls. ...
... For the stability analysis method of the filling stope, Mitchell [22] proposed a method considering the stope size and assuming the slip plane for calculating the stability of the CPB stope, which is the application of the limit-equilibrium slip in the backfill mining. Liu et al. [23]. considered the time factor of the cemented backfill stope, analyzed the applicability of the Mitchell method, and believed that the results of the Mitchell solution were closer to the situation under short-term undrained conditions than long-term drainage conditions for the CPB stope. ...
... However, with the development of computing technology, more complex environmental models have been taken into account, in which blasting-induced damage For the stability analysis method of the filling stope, Mitchell [22] proposed a method considering the stope size and assuming the slip plane for calculating the stability of the CPB stope, which is the application of the limit-equilibrium slip in the backfill mining. Liu et al. [23]. considered the time factor of the cemented backfill stope, analyzed the applicability of the Mitchell method, and believed that the results of the Mitchell solution were closer to the situation under short-term undrained conditions than long-term drainage conditions for the CPB stope. ...
The sublevel open stoping with backfill method has recently been widely used in underground metal mines. The primary CPB stope is frequently affected by blasting in the secondary ore stope, leading to stope collapse and ore dilution, which has become a common problem and has received widespread attention. Numerical simulations are carried out in the present work, and a 1/4 numeral model consisting of a primary CPB stope and a secondary ore stope is built. The secondary ore stope is divided into four layers on average in the simulation model, and the incident stress induced by each blasting at the interface of the CPB and ore is simulated. The results show that the CPB stope in the range within the height of the explosive charge induced horizontal compressive stress and tensile stress induced from the explosive charge height, while the mined section under the charge height has no obvious blasting impact. The maximum incident compressive stress is close to 1.2 MPa and occurs in the area closest to the blast hole The maximum induced tensile stress occurs in the range above the charge height, which is about 0.2 MPa. The stress ratios of the four-layered lift blasts are 3.6%, 3.8%, 4.0%, and 4.8%, respectively, showing a slight cumulative effect of layered blasting. In addition, the positive correlation between incident stress and the stress ratio is studied in the present work, and the results show that the greater the incident stress is, the greater the incident ratio is.
... In addition, with the gradual depletion of shallow mineral resources, mines around the world have become deeper, high ground stress, and rockburst are the key factors leading to goaf instability . To solve the above problems, cemented tailings backfill (CTB) is widely used in underground mines around the world because of its ability to effectively control ground pressure, reduce surface settlement, and manage tailings (Liu et al., 2016;Zhao et al., 2017;Cao et al., 2019a;. CTB is a complex composite material produced by mixing tailings (70-80 wt%), cementing materials (3-7 wt%), and a corresponding proportion of water, which is then transported to underground stopes by gravity or pumping Xue et al., 2019a). ...
This special issue draws attention to “Non-BF slag Based Green Cementitious Materials”, focusing on the research progress and achievements of non-BF slag-based green cementitious materials. Metallurgical slag is a kind of by-product of the metal smelting process. For many years, a huge amount of slag was deposited in waste dumps or stockpiles due to the increasing scale of metal production, which causes a series of social, environmental, and economic problems. The sustainable utilisation of waste slag has become one of the major challenges in the field of civil and environmental engineering. The use of slag in cement production as an alternative cementitious material to form new green construction materials is a critical aspect to consume this huge amount of metallurgical solid waste. So far, blast-furnace slag (BF slag) has already been widely used in cement production, however, a large amount of non-BF slag (ferrous and non-ferrous) materials are still under-utilized. At present, a lot of research has been carried out to investigate the use of non-BF slags in cement production. However, only a few examples of industrial applications have been reported. Various Research Topics are available to address this issue related to the role of non-BF slag-based green cementitious materials, including hydration and microstructure formation of green cementitious materials; assessment of mechanical properties of green cementitious materials; methods to improve the activity of non-BF slag-based green cementitious materials; results from laboratory experiments and/or large-scale projects; short and long-term performance of novel cementitious materials; case studies of green cementitious materials for mine filling.
In the present issue of Frontiers in Materials, a total of 29 manuscripts were received and 19 of them were accepted. The editors would thank all the experts and scholars for submitting excellent papers to this special issue, and the reviewers for providing many constructive comments for the special issue.
... Mines produce large volumes of mine waste each year in terms of tailings and waste rocks [1]. A small portion of these materials can be sent back to underground voids as backfill [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. The recycling and reuse of these materials for in-and out-mine sites are also increasingly seen [19]. ...
... Processes 2022,10, 898 ...
Tailings storage facilities (TSFs) are known as a time-bomb. The numerous failures of TSFs and the heavy catastrophic consequences associated with each failure of TSFs indicate that preventing measures are necessary for existing TSFs. One of the preventing measures is to construct catch dams along the downstream near TSFs. The design of catch dams requires a good understanding of the dynamic interaction between the tailing slurry flow and the catch dams. There are, however, very few studies on this aspect. In this study, a numerical code, named LS-DYNA, that is based on a combination of smoothed particle hydrodynamics and a finite element method, was used. The numerical modeling shows that the tailings slurry flow can generally be divided into four stages. In terms of stability analysis, a catch dam should be built either very close to or very far from the TSF. When the catch dam with an upstream slope of a very small inclination angle is too close to the tailings pond, it can be necessary to build a very high catch dam or a secondary catch dam. As the impacting force can increase and decrease with the fluctuations back-and-forth of the tailing slurry flow, the ideal inclination angle of the upstream slope of the catch dam is between 30° and 37.5°, while the construction of a catch dam with a vertical upstream slope should be avoided. However, a catch dam with steeper upstream slopes seems to be more efficient in intercepting tailings flow and allowing the people downstream more time for evacuation. All these aspects need to be considered to optimize the design of catch dams.
... The analytical solution was validated by laboratory box instability test results. Through numerical modeling, Liu et al. (2016a) have shown that the analytical solution and laboratory tests of are all for backfill under undrained condition for short-term stability analysis, not for backfill under fully drained condition for long-term stability analysis. ...
... The failure mechanism of side-exposed backfill associated with stiff and immobile rock walls has been investigated by Mitchell and coworkers Mitchell 1986Mitchell , 1989) through laboratory tests, which show that wedge sliding is the main control failure mechanism. This has been further confirmed by Li and coworkers Liu et al. 2016aLiu et al. , 2018Yang et al. 2017a) through numerical modeling when the backfill cohesion is Horizontal closure at the side wall center of the reference case during 28 days after extracting the primary stope by considering parameters shown in Table 1 Table 3 Characteristics of numerical simulation cases (with γ = 18 kN/m 3 , ν = 0.3, ψ = 0°, T = UCS/10 for cemented backfill, Time-Dependent Stability Analyses of Side-Exposed Backfill Considering Creep of Surrounding… low. When the backfill cohesion is high, tension cracks can occur on top part of the side-exposed backfill and the instability is mostly exhibited by the fall of a spoon-like block (Yang et al. 2017a). ...
... The applicability of FLAC 3D to studying the stability of side-exposed backfill has been verified by Liu et al. (2016a) and Wang et al. (2021) through the reproductions of box instability and centrifugal model tests (Mitchell 1986). Nonetheless, more experimental works are still needed to verify the numerical model considering creep of rock mass. ...
The stability of side-exposed backfill is essential to ensure a successful mining operation. Until now, it has been analyzed without considering the creep of rock mass. In practice, stope excavation and backfilling are always scheduled with different time during which fill mechanical properties can evolve and rocks exhibit more or less creep deformation. In this study, time-dependent stability and minimum required cohesion (cmin) of side-exposed backfill associated with the creep of surrounding rock mass are, for the first time, analyzed through numerical modeling with FLAC3D. A distinction is made between the cohesion at failure and cmin. Results show that the empty time of primary stope does not significantly affect the stability and cmin. When mine depth is small and the rock exhibits little creep, it deserves to wait longer time before adjacent extraction for the backfill to gain more strength. When the mine depth is large or/and the rock exhibits heavy creep, the instability of side-exposed backfill can be dictated by crushing failure. A stronger backfill means also a harder backfill, which absorbs larger compressive stress and is more prone to be crushed. In this condition, a softer backfill can be better through the use of lower binder content or/and with a shorter curing time. The adjacent secondary stope should be filled as soon as possible to avoid failure of side-exposed backfill. More simulations were done on the effects of stope geometry and mechanical properties of backfill and rock mass on the stability and cmin of side-exposed backfill.
