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The development of an efficient and environmentally friendly dust suppressant is crucial to address the issue of dust pollution in limestone mines. Leveraging the synergistic microbial-induced calcium carbonate precipitation (MICP) technology involving NaHCO3 and dodecyl glucoside (APG), the optimal ratio of the dust suppressant was determined through single-factor and response surface tests. The dust suppression efficacy and mechanisms were analyzed through performance testing and microscopic imaging techniques, indicating that the optimal ratio of the new microbial dust suppressant was 20% mineralized bacteria cultured for 72 h, 0.647 mol L−1 cementing solution, 3.142% NaHCO3, and 0.149% APG. Under these conditions, the yield of calcium carbonate increased by 24.89% as compared to when no NaHCO3 was added. The dust suppressant demonstrated excellent wind, moisture, and rain resistance, as well as curing ability. More calcite was formed in the dust samples after treatment, and the stable form of the dust suppressant contributed to consolidating the limestone dust into a cohesive mass. These findings indicate that the synergistic effect of NaHCO3 and APG significantly enhanced the dust suppression capabilities of the designed microbial dust suppressant. [ABSTRACT FROM AUTHOR]

To achieve integrated resource utilization of graphite tailings to improve their water-holding capacity, river silt and cow dung powder were added to graphite tailings as organic matter improvers. Improver ratios were designed using 4 g cow dung powder and 20, 30, and 50 g river silt. Soil–water characterization tests were performed using a combined tensiometer and filter paper method based on optimum density measurements. Analysis of the influence of river silt dosing on the soil–water characteristic curves of improved graphite tailing specimens was performed with data fitting using the Van Genuchten model. Here, we investigated the effect of river silt dosing on the internal pore structure and water-holding capacity of modified graphite tailing samples and verified the applicability of the model to graphite tailings. Our results demonstrate that the organic matter improver incorporated into graphite tailings can improve the internal structural compactness of graphite tailings, improving the water holding capacity. With an increase in river silt dosage, the saturated water content is larger, and the residual water content increases and then decreases. When river silt dosage is 30 g, the residual water content is the highest at a value of 3.32%. The van Genuchten model was highly accurate for assessing the graphite tailings. With an increase in river silt doping, the internal pore space first decreased and then increased, and the internal structure gradually became compact and loosened. The internal structure was in the optimal state in the experimental study when the dosage of cow dung powder was 4 g and the dosage of river silt was 30 g. The water holding capacity was optimal at this time. The results of this study provide a theoretical foundation for graphite-tailing-based mine reclamation and play a guiding role in exploring the value of the hydraulic characteristic index parameters when applying graphite tailings engineering. [ABSTRACT FROM AUTHOR]

To investigate the influence of a geogrid-reinforced tailings dam on the seepage stability of the dam body, this paper was based on the field test of a reinforced tailings accumulation dam. The study utilized the finite element strength reduction method to simulate the stability of the main dam of the Fengshuigou tailings reservoir under different seepage conditions using ABAQUS software. Additionally, the paper discussed the impact of conventional heightening, dry beach length, and geogrid reinforcement on the position and safety factor of the saturation line of the dam body. The results showed that when the dam body was raised, the saturation line rose by 2.8–5.3 m, resulting in a decrease in the safety factor. The geogrid effectively reduced the height of the saturation line in the tailings dam. In comparison to the unreinforced condition (dam heightening), the saturation line of the tailings dam decreased by 0.9–2.8 m under the local reinforcement condition and by 3.2–12.5 m under the overall reinforcement condition. The geogrid significantly improved the stability of the tailings dam. Furthermore, under the local reinforcement condition, the safety factor of the dam increased by 3.8–5.5%, and under the overall reinforcement condition, it increased by 35.9–42.9%, when compared to the unreinforced condition. Increasing the dry beach length improved the stability of the tailings dam, and under normal working conditions, the safety of the tailings dam was much higher than under the minimum dry beach condition. These results served as a reference for the design of the dam and the new tailings reservoir, laying a foundation for the sustainable development and environmental protection of the tailings pond. [ABSTRACT FROM AUTHOR]

There is a high risk of dam breakage in tailing reservoirs under extreme conditions. Once a dam breaks, it causes serious pollution to the surrounding ecological environment. To explore the effects of a tailings dam break under extreme conditions (flood conditions, drainage failure, flood discharge failure, and dam saturation), the mechanism underlying an overtopping dam break must be accurately understood. In this study, fine-grained tailings and perlite were selected to create composite model sand, and a prototype tailing reservoir was restored at a scale of 1:200. Furthermore, the dam-break process and results were analyzed and summarized by performing an overtopping dam-break test on the tailing reservoir under extreme conditions. The results show that the tailing discharge process has a high sand content, strong sand-carrying capacity, and high speed. The amount of model sand discharge accounted for 15.13% of the total storage capacity, and the amount of tailings deposition in the downstream area accounted for 95.21% of the discharge, which were both greater than the results of similar physical model tests and actual tailings dam failure accidents. An overtopping dam break in a tailing pond is a progressively destructive process. The dam break mechanism can be divided into two stages: prior breach penetration and subsequent breach horizontal expansion. In the process of a tailings dam break, the motion state of the tailings particles is transformed between the bed-load and suspended-load movement states. These results can provide important reference for the reinforcement of mine management and the formulation of preventive measures, which are essential to improving the safety of tailings reservoirs and protecting the ecological environment. [ABSTRACT FROM AUTHOR]

To realize the resourceful use of soilbags filled with graphite tailings, their load-bearing and deformation characteristics must be fully understood. In this study, the following results were obtained by performing geometric testing of water-filled sealing bags and uniaxial compression tests of soilbags filled with graphite tailings. The volume of the soilbag expressed in rectangular form was approximately 0.773 times the actual volume. The types of compression damage to soilbags can be defined as surface damage and overall damage. The surface damage load increases with decreasing filling density and decreases with decreasing soilbag size. Moreover, the higher the tensile capacity of the soilbag material and the lower the friction between the soilbags, the greater the surface damage load. The overall damage load increased with an increase in the tensile strength of the soilbag material and decreased with an increase in the degree of filling; the overall damage load was greater for large-sized soilbags at high degrees of filling. Thus, the existing theoretical calculation method cannot accurately calculate the damage load of soilbags filled with graphite tailings, and the test results deviate from the theoretical calculation results, with the latter showing an increasing damage load with a decreasing filling degree. [ABSTRACT FROM AUTHOR]

The dynamic stability of tailing ponds depend largely on the dynamic characteristics of tailings sand. To explore the dynamic characteristics of tailings sand under different consolidation conditions, consolidated undrained triaxial tests under different dry densities, consolidation ratios and containing pressures, the dynamic shear stress, liquefaction stress ratio, dynamic strength index, dynamic pore water pressure, dynamic modulus, and damping ratio of tailings sand under different consolidation conditions were analyzed. The dynamic shear stress linearly changed with the number of failure vibrations. The liquefaction stress ratio increases with an increase in consolidation ratio, conforming to the quadratic polynomial of the origin. With an increase in failure vibration times, the dynamic internal friction angle decreases gradually. Under different failure vibration times, the dynamic internal friction angle increases with an increase in consolidation ratio and dry density. An exponential function model of dynamic pore pressure growth suitable for equal pressure and bias consolidation conditions is proposed, and the fitting effect is favorable. The dynamic shear modulus ratio decreases with an increase in dynamic shear strain; the damping ratio increases with an increase in dynamic shear strain. The research results can provide a theoretical reference for seismic liquefaction of tailings dams in high-intensity seismic areas. [ABSTRACT FROM AUTHOR]

Graphite tailings, a type of waste material, pose significant environmental and human health risks when stored in tailing ponds. One effective large-scale recycling method for these tailings is to use them as fill for soilbags, which can then be applied to support areas along empty lanes. This study examines the vertical bearing capacity of soilbags filled with graphite tailings. Uniaxial unconfined compression tests were conducted to determine the effects of filling degree, unit-area mass, and the inclusion of geogrid reinforcement on the vertical bearing capacity of the soilbags. To investigate the vertical bearing capacity of soilbagged graphite tailings, the impact of filling degree, unit area mass of the soilbag, and geogrid reverse wrapping on the vertical bearing capacity of the soilbag were explored via uniaxial unconstrained compression tests. This study introduces and assesses several classical models for load-bearing in multi-layer soilbag stacks, presents modifications to the soilbag wrap sand semi-circular boundary model, and conducts a comparative analysis. Experimental findings suggest that the initial failure in soilbags is predominantly at the interface contact. Even during this failure, the lateral sides of the soilbags maintain significant confinement ability, allowing continued load-bearing. The rupture of a soilbag is evident when it is compressed to the point of lateral cracking, and this is accompanied by the leakage of lateral graphite tailings. The employment of reverse encapsulation techniques with geogrids can delay the total failure of these bags, thereby significantly improving their load-bearing capability. Compared to the traditional stress model for multi-layer soilbag stacks, the modified multi-mode soilbag wrap sand semi-circular boundary model provides a more accurate prediction of stress when a three-layer soilbag stack, with a filling degree exceeding 75%, faces initial failure. The research findings provide a reference for the feasibility of using soilbagged graphite tailings in the construction of mine roadways along empty lanes. [ABSTRACT FROM AUTHOR]

This study investigates the shear characteristics of soil-rock mixtures, a critical factor influencing slope stability in engineering construction. Soil-rock mixtures, often exhibit poor integrity and can easily soften in water due to geological influences. The YT1200 direct shear drawing friction system was employed to conduct shear tests, analyzing the effect of varying water content and fine particle mass fraction under different normal stresses. Utilizing fractional derivatives, we formulated a fractional derivative shear model. Test results illustrated a softening phenomenon post achieving peak shear stress in the soil-rock mixture. It was found that peak shear stress is directly proportional to the normal stress, and inversely proportional to both water content and fine particle mass fraction. Additionally, the cohesion and internal friction angle decrease according to a power function with increasing water content, and non-linearly decrease with the rise of fine particle mass fraction. The proposed shear model aptly simulates the entire shear failure process of the soil-rock mixture, effectively analyzing the influence of key factors on shear characteristics. These findings contribute to the strength prediction and numerical simulation of soil-rock mixtures, thereby aiding in the design of reinforcement schemes and slope stability analysis. [ABSTRACT FROM AUTHOR]

Tailing ponds are a major hazard source with the risk of dam breaks. To predict the impact of tailings pond dam breaks more accurately, one needs to quantitatively understand the dam-breaking process of the tailings reservoir and its downstream impact. This study is based on an old tailings pond that is about to be put out of service and the proposed new tailings pond next to it. Study the inundation range of the new and old tailing ponds with simultaneous overtopping dam breaks under actual terrain conditions. First, fine-grained tailings and expanded perlite were selected as the model sand materials, and the appropriate model sand ratio was determined through laboratory tests. Second, the two tailings ponds were tested (at a scale of 1:200), for flood overtopping and simultaneous dam breaks. The dam break, flow, section morphology evolution, submerged elevation, and range were analyzed. Finally, a numerical model was developed using MIKE 21 to simulate the simultaneous overtopping and collapse of the new and old tailings ponds, and the impact of rainfall intensity on the inundation range of the simultaneous overtopping of the dam was analyzed. The research results will guide disaster prevention and mitigation in tailings reservoirs. [ABSTRACT FROM AUTHOR]

This study aimed to explore the retardation characteristics of different geogrid-reinforced layers and mesh sizes in the failure process of a reinforced tailings dam. The Qidashan tailings of Ansteel Mining were considered as the engineering background. The tailings-dam model test was conducted by laying a geogrid in the tailings dam. We analyzed the effects of different reinforcement layers and mesh sizes of reinforced tailings dams on the surface settlements, phreatic lines, and vertical pressures within the dam body. We explored and tested the reinforcement mechanism and its effect. The test results indicate that the final surface settlement yields a positive correlation with an increase in the number of reinforced layers. The surface settlement increases rapidly at first before becoming stable as the geogrid mesh size decreases. The phreatic line of the dam body can be reduced considerably by increasing the number of reinforcement layers. Moreover, a reasonable mesh size of the reinforcement can reduce the phreatic line of the dam body. The vertical pressure inside the dam decreases considerably as the number of reinforced layers increases. With a smaller geogrid mesh size, vertical pressure inside the dam body decreases. Therefore, reinforcement has a significant retarding effect on the development of tailing accumulation dam failure and enhances its stability. [ABSTRACT FROM AUTHOR]

Tailings dams are in danger of liquefaction during earthquakes. The liquefaction process can be indirectly reflected by the evolution rule of the dynamic pore water pressure. To study the development law of dynamic pore water pressure of tailing sand under different consolidation conditions, the evolution equation of critical dynamic pore water pressure of tailings under isotropic and anisotropic consolidation conditions was derived based on the limit equilibrium theory. Moreover, the development law of dynamic pore water pressure was expounded theoretically. The dynamic triaxial tests of tailing silty sand and tailing silt under different dry densities, consolidation ratios, and confining pressures were performed. The dynamic pore water pressure ratio and vibration ratio curves of tailings under isotropic and anisotropic consolidation were analyzed, and a dynamic pore water pressure growth index model suitable for both isotropic and anisotropic consolidation was derived. The results showed that the critical dynamic pore water pressure was positively correlated with the confining pressure and average particle size of tailings under isotropic consolidation conditions. The tailings have a limit dynamic effective internal friction angle φdc under the anisotropic consolidation condition. The evolution law of critical dynamic pore water pressure can be judged according to the dynamic effective internal friction angle of tailing sand φd and φdc values. The consolidation ratio significantly affects the dynamic pore pressure growth curve while confining pressure and dry density do not. For different tailing materials, the dynamic pore water pressure ratio is positively correlated with tailing particles. The dynamic pore water pressure growth process of tailing silty sand and tailing silt can be divided into two stages: rapid and stable growths. The development law of two types of tailings can be described by the dynamic pore water pressure growth index model. The research results can provide a theoretical basis for the seismic design of tailings dams in practical engineering. [ABSTRACT FROM AUTHOR]

Considering the strain-softening characteristics of the pull-out interface between geotextiles and tailings; to determine the interface interaction characteristics, this paper proposes a trilinear shear stress displacement softening model of geotextile-reinforced tailings. The obtained nonlinear governing equations were dimensionless, which were expressed in finite difference form. The results indicated that an accurate numerical solution could be obtained within a reasonable calculation time by discretizing the reinforcement length into 300 units. Three new dimensionless interaction terms, namely, the relative stiffness α, relative displacement β, and relative interface shear stiffness η of the reinforcement-tailings interaction, were introduced. In addition, an estimation method based on the approximate value of the relative stiffness α of the reinforcement-soil interface in the low-tensile-force displacement range was proposed. The interface shear stress range according to parameters α, β, and η was parameterized, and the normalization relationship between the tensile force and pull-out end displacement was determined. The numerical values calculated by the model were compared with the pull-out test results, demonstrating that the proposed model can accurately predict the pull-out behavior of the extensible reinforcement. [ABSTRACT FROM AUTHOR]

The aim of this study was to explore the correlation between mesoparameters (normal stiffness k n , tangential stiffness k s , and friction coefficient fric) and macromechanical parameters (cohesion, internal friction angle, and peak principal stress as well as its corresponding stress variables) of the particle flow code in 3-dimension (PFC3D) built-in linear contact model, which is suitable for simulating cohesionless materials that are similar to tailing sand. A triaxial test model was established using PFC3D, and nonspherical particles were developed by the clump command. Several numerical triaxial tests were performed under different confining pressures and mesoparameters. The results showed that the linear contact model is effective in simulating sandy soil, and the corresponding gradation of particles should be given. No one-to-one correspondence was found between the macromechanical parameters and the mesoparameters. Each macromechanical parameter was most affected by a certain mesoparameter, and the degree of influence was much greater than that of the other mesoparameters. The macro- and mesoparameters were strongly correlated. The stiffness ratio ( k n / k s ) mainly affected the cohesion value, the friction coefficient of fillers (pebble-fric) mainly affected the internal friction angle and the peak principal stress, the normal stiffness ( k n ) of particles mainly affected the strain corresponding to the peak principal stress, and the influence of the side wall friction coefficient (wall-fric) was not the strongest but was non-negligible. The microparameter calibration of the contact model can follow the order of parameter adjustment proposed in this study, which can facilitate and enhance the accuracy of the parameter calibration process of the linear contact model. [ABSTRACT FROM AUTHOR]

Currently, the influence of geogrid mesh size on interface characteristics are disregarded in various codes and standards. To explore the reasonable mesh size of geogrid used for reinforced tailings, the direct shear test and pull-out test of geogrid reinforced tailings with different mesh sizes were done. The results show that the shear surface of geogrid reinforced tailings is characterized by the combined action of geogrid-tailings interface and tailings-tailings interface; the geogrid-tailings interface friction was separated from the comprehensive interface friction to analyze the influence of area ratio on it under different test conditions; and the mesh size of geogrid reinforced tailings, that is, the area ratio of the geogrid-tailings interface to the shear surface (α), has a greater influence on the pseudo-cohesion and less on the pseudo-friction angle. The friction strength of the geogrid-tailings interface increases slightly with increasing mesh size, then decreases sharply, and the reinforcement effect of geogrid quickly disappears. Considering the direct shear test and pull-out test, the reasonable mesh size of geogrid reinforced tailings should be the mesh size corresponding to α 0.47–0.55. With the increase α, the effect of the geogrid reinforced tailings can be divided into four stages where the third stage ( 0.4 ≤ α < 0.6 ) is the stage with the best reinforcement effect. [ABSTRACT FROM AUTHOR]

The existing geogrid constitutive model does not consider its damage effects under high stress. To analyze the mechanical properties (creep and stress relaxation) of geogrids under arbitrary loading history conditions while considering the different creep characteristics of geogrids under different load levels, it is considered that the geogrid exhibits elastic strain, plastic strain, and viscoelastic strain when it is at a low stress level, and a viscoelastic-plastic model that can reflect the attenuation creep under low stress level is established. Furthermore, when the geogrid is at a high stress level, in addition to the strain at a low stress level, the damage effects of the geogrid needs to be considered, and a viscoelastic-plastic damage model reflecting the non-attenuation creep under high stress levels is established. Both models are composed of spring, plastic element, and Kelvin body in series. The research results show that the two constitutive relations of the proposed geogrid can better match the test results under different stress levels and can predict the stress relaxation of the geogrid well. According to the creep curve fitting of the geogrid, the relationship between the critical time and stress change considering the damage of the geogrid can be obtained, and then the stress range that needs to be considered for the damage of the geogrid can be determined; the stress–strain relationship of the plastic element changes in the form of a hyperbola passing through the origin. These results can provide a scientific basis for studying the performance of geogrids under long-term loads and analyzing their creep reduction coefficients. [ABSTRACT FROM AUTHOR]

In order to compare and analyze the difference in deformation and damage law of soft and hard porous media materials, the digital image correlation is used to evaluate the heterogeneous development of strain fields of hard and brittle raw coal material and soft plastic briquette coal material under uniaxial compression. Through the defined statistical indicator, the quantitative characterization of deformation localization is realized, and the material damage constitutive model based on the statistical indicator of strain field is established. The results show that the yield stage of raw coal is not obvious, showing the characteristics of strain hardening and X-shaped macroscopic shear failure. The yield stage of briquette coal is more obvious, showing the characteristics of strain softening and a tensile failure mode. The progress of strain localization can well reflect the damage and destruction process of materials. The progress of strain localization of briquette coal can be divided into uniform deformation stage, localization stage, and failure stage, while the stage characteristics of localized evolution of raw coal is not obvious. The theoretical results of the damage constitutive model defined by statistical indicator are in good agreement with the experimental data and can well reflect the stress and strain characteristics of the two materials. [ABSTRACT FROM AUTHOR]

Aiming at the strain-hardening and strain-softening phenomena between geosynthetics and tailings during pull-out tests, bilinear and trilinear shear stress-displacement softening models were proposed. The pull-out process of the hardening reinforcement was divided into the elastic stage, elastic-hardening transition stage, and pure hardening stage. The pull-out process of the softened reinforcement was divided into the elastic stage, elastic-softening transition stage, pure softening stage, softening-residual transition stage, and pure residual stage. The expressions of the interface tension, shear stress, and displacement at the different stages under a pull-out load were derived through the interface basic control equation. At the same time, the evolution law of the interface shear stress at different pull-out stages was analysed, and the predicted results of the two elastic-plastic models were compared with the experimental results. The results show that the predicted results are in good agreement with the experimental data, which verifies the validity of the proposed two elastic-plastic models for the progressive failure analysis of reinforcement at the pull-out interface. During the process of pull-out, the transition stage is not obvious. When the reinforcement is in the elastic stage, the nonlinearity and maximum value of the interface shear stress increase with an increase in the elastic shear stiffness, while the tensile stiffness shows the opposite trend. When the reinforcement is in the hardening or softening stage, the larger the hardening (softening) shear stiffness is, the larger the change range of shear stress is and the more obvious the hardening (softening) characteristics of the reinforcement are. The results comprehensively reflect the progressive failure of reinforcement-tailing interfaces with different strain types and provide theoretical support for the study of the interface characteristics of geosynthetic-reinforced tailings. [ABSTRACT FROM AUTHOR]

Owing to the complexity of current reinforcement mechanisms, test results from existing models alone cannot provide a basis for the design of new tailings dam reinforcement projects. On-site reinforced tailings accumulation dam testing is thus required to further understand the reinforcement mechanism. In this study, the influence of reinforcement on tailings dams and the variation law of pore water pressure (PWP) and internal pressure (IP) in the dam body after slurry discharge were analysed, and a comparative analysis was performed. The results showed that during the field test, the PWP and internal earth pressure of the accumulation dam after grouting gradually increased over time. Reinforcement can greatly reduce the PWP and IP of the reinforced dam; compared with geotextiles, the reinforcement effect of geogrids is slightly greater. Based on these results, we conclude that geosynthetics are a good choice for strengthening tailings accumulation dams. [ABSTRACT FROM AUTHOR]

To evaluate the shear properties of geotextile-reinforced tailings, triaxial compression tests were performed on geogrids and geotextiles with zero, one, two, and four reinforced layers. The stress–strain characteristics and reinforcement effects of the reinforced tailings with different layers were analyzed. According to the test results, the geogrid stress–strain curves show hardening characteristics, whereas the geotextile stress–strain curves have strain-softening properties. With more reinforced layers, the hardening or softening characteristics become more prominent. We demonstrate that the stress–strain curves of geogrids and geotextile reinforced tailings under different reinforced layers can be fitted by the Duncan–Zhang model, which indicates that the pseudo-cohesion of shear strength index increases linearly whereas the friction angle remains primarily unchanged with the increase in reinforced layers. In addition, we observed that, although the strength of the reinforced tailings increases substantially, the reinforcement effect is more significant at a low confining pressure than at a high confining pressure. On the contrary, the triaxial specimen strength decreases with the increase in the number of reinforced layers. Our findings can provide valuable input toward the design and application of reinforced engineering. [ABSTRACT FROM AUTHOR]

In the field of Fuel Cell Electric Vehicles (FCEVs), a fuel-cell stack usually works together with a battery to improve powertrain performance. In this hybrid-power system, an Energy Management Strategy (EMS) is essential to configure the hybrid-power sources to provide sufficient energy for driving the FCEV in different traffic conditions. The EMS determines the overall performance of the power supply system; accordingly, EMS research has important theoretical significance and application values on the improvement of energy-utilization efficiency and the serviceability of vehicles' hybrid-power sources. To overcome the deficiency of apparent filtering lag and improve the adaptability of an EMS to different traffic conditions, this paper proposes a novel EMS based on traffic-condition predictions, frequency decoupling and a Fuzzy Inference System (FIS). An Artificial Neural Network (ANN) was designed to predict traffic conditions according to the vehicle's running parameters; then, a Hull Moving Average (HMA) algorithm, with filter-window width decided by the prediction result, is introduced to split the demanded power and keep low-frequency components in order to meet the load characteristics of the fuel cell; afterward, an FIS was applied to manage power flows of the FCEV's hybrid-power sources and maintain the State of Change (SoC) of the battery in a predefined range. Finally, an FCEV simulation platform was built with MATLAB/Simulink and comparison simulations were carried out with the standard test cycle of the Worldwide harmonized Light vehicle Test Procedures (WLTPs). Simulation results showed that the proposed EMS could efficiently coordinate the hybrid-power sources and support the FCEV in following the reference speed with negligible control errors and sufficient power supply; the SoC of the battery was also maintained with good adaptability in different driving conditions. [ABSTRACT FROM AUTHOR]