Impact of modifiers on soil-water characteristics of graphite tailings.

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.

Analysis of compression damage pattern and strength influencing factors in graphite-tailing-filled soilbags.

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.

Experimental study on dynamic characteristics of tailings under different consolidation conditions.

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.

Seepage stability analysis of geogrid reinforced tailings dam.

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.

Experimental study on overtopping dam-break of a tailing reservoir under extreme conditions.

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.

Study of shear properties and shear model of soil-rock mixture.

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.

Impact of inundation range of overtopping dam break of tailings pond under actual terrain conditions.

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.

Development law and growth model of dynamic pore water pressure of tailings under different consolidation conditions.

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 [Formula: see text] 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 [Formula: see text] 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.

Analysis of interface mechanical properties between geotextiles and tailings during pull-out tests.

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 ß, 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, ß, 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.

Experimental study of reasonable mesh size of geogrid reinforced tailings.

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 ([Formula: see text]) is the stage with the best reinforcement effect.

Triaxial Testing of Geosynthetics Reinforced Tailings with Different Reinforced Layers.

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.