Search Results (8)

Underground coal mining induces surface subsidence, which in turn impacts the stability of slopes in mountainous regions. However, research that investigates the coupling relationship between surface subsidence in mountainous regions and the occurrence of multiple surface hazards is scarce. Taking a coal mine in southwestern China as a case study, a detailed catalog of the surface hazards in the study area was created based on multi-temporal satellite imagery interpretation and Unmanned aerial vehicle (UAV) surveys. Using interferometric synthetic aperture radar (InSAR) technology and the logistic subsidence prediction method, this study investigated the evolution of surface subsidence induced by underground mining activities and its impact on the triggering of multiple surface hazards. We found that the study area experienced various types of surface hazards, including subsidence, landslides, debris flows, sinkholes, and ground fissures, due to the effects of underground mining activities. The InSAR monitoring results showed that the maximum subsidence at the back edge of the slope terrace was 98.2 mm, with the most severe deformation occurring at the mid-slope of the mountain, where the maximum subsidence reached 139.8 mm. The surface subsidence process followed an S-shaped curve, comprising the stages of initial subsidence, accelerated subsidence, and residual subsidence. Additionally, the subsidence continued even after coal mining operations concluded. Predictions derived from the logistic model indicate that the duration of residual surface subsidence in the study area is approximately 1 to 2 years. This study aimed to provide a scientific foundation for elucidating the temporal and spatial variation patterns of subsidence induced by underground coal mining in mountainous regions and its impact on the formation of multiple surface hazards. Full article

In mines where the natural caving method is used, the frequent occurrence of underground debris flows and the complex mine environments make it difficult to prevent and control underground debris flows. The source is one of the critical conditions for the formation of debris flows, and studying the impact of source material gradation on underground debris-flow disasters can effectively help prevent and control these occurrences. This paper describes a multiscale study of underground debris flows using physical model experiments and the discrete-element method (PFC^3D) to understand the impact of the source material gradation on the disaster mechanism of underground debris flows from macroscopic and microscopic perspectives. Macroscopically, an increase in content of medium and large particles in the gradation will enhance the instantaneous destructive force. Large particles can more easily cause disasters than medium and fine particles with the same content, but the disaster-causing ability is minimized when the contents of medium and large particles exceed 50% and 60%, respectively. With increasing fine particle content, the long-distance disaster-causing ability and duration is increased. On the microscopic level, the source-level pairs affect the initial flow mode, concentration area of the force chain, average velocity, average runout distance, and change in energy of the underground debris flow. Among them, the proportion of large particles in the gradation significantly affects the change in kinetic energy, change in dissipative energy, time to reach the peak kinetic energy, and time of coincidence of dissipative energy and gravitational potential energy. The process of underground debris flow can be divided into a “sudden stage”, a “continuous impact stage”, and a “convergence and accumulation stage”. This work reveals the close relationship between source material gradation and the disaster mechanism of underground debris flows and highlights the necessity of considering the source material gradation in the prevention and control of underground debris flows. It can provide an important basic theory for the study of environmental and urban sustainable development. Full article

In order to effectively reduce the risk of underground debris flow, surface moraine is solidified and modified by using grouting technology to realize the change in fine-grained moraine from “powder” to “block” to change the source conditions of underground debris flow and to reduce the risk of moraine from the root. In this paper, the effects of grouting pressure, porosity, and pore diameter on the spillability of moraine are investigated experimentally. The results show that the grouting depth increases linearly with increasing sample porosity. For the same sample density, the grouting pressure is proportional to the grouting depth. As the pore diameter of the sample increases, the longitudinal grouting depth of the sample increases, but the transverse diffusion distance decreases. The chemical grout in the moraine is mainly split-infiltration grouting mode. The present research results can provide effective support for the prevention and control of underground debris flow in Pulang Copper Mine. Full article

Stump–root systems consist of aboveground stumps and underground coarse roots after timber harvesting. Stump–root systems are the primary source of coarse woody debris (CWD) in plantations, and they play a crucial role in the material cycle, energy flow, and biodiversity of Eucalyptus plantation ecosystems. However, there is limited knowledge about the changes in elemental stock within this CWD type during decomposition. To address this gap, we conducted a study on Eucalyptus urophylla × E. grandis stump–root systems at various times (0, 1, 2, 3, 4, 5, and 6 years) after clearcutting. Our aim was to investigate the stock changes in eight elements (K, Ca, Mg, S, Fe, Mn, Cu, and Zn) within the stumps and coarse roots over time and their decay levels, and we analyzed the relationship between elemental stocks and the physical, chemical, and structural components of stump–root systems. Our findings revealed the following: (1) The majority of each element’s stock within the stump–root system was found in the coarse roots. The elemental stocks in both stumps and coarse roots decreased as time passed after clearcutting and as decay progressed. (2) Notably, the elemental stocks in stumps and coarse roots were significantly higher than in other treatments during the initial 0–2 years after clearcutting and at decay classes I and II. In terms of elemental stocks, stumps from all clearcutting times or decay classes had the highest K stock, followed by Ca and Fe. Mg, Mn, and S stocks were lower than the first three, while Zn and Cu stocks were very low. The ordering of elemental stocks from high to low in the stump–root systems generally aligned with that of the coarse roots. (3) The residual rates of K, Mg, and Mn stocks in the stump–root systems fit the negative exponential model well. It took approximately 1 to 3.5 years for a 50% loss of the initial stocks of these elements and 5 to 10 years for a 95% loss. (4) The large amount of biomass in the stump–root system is the long-term nutrient reservoir of plantations, and any factor related to biomass loss affects the magnitude and duration of the nutrient reservoir, such as N, P, stoichiometric ratios, density, water-holding capacity, and hemicellulose. These findings contribute to a better understanding of the nutrient elemental dynamics and ecological functions of stump–root systems in Eucalyptus plantations. Full article

Sudden debris flows in underground mines are characterized by strong burstiness, great destructiveness, and difficult monitoring. Traditional single monitoring methods can only roughly judge the probability of underground debris flow occurrences through one-sided potential phenomena, making it difficult to accurately predict sudden underground debris flows. Therefore, effective monitoring methods can prevent or reduce waste and damage to mineral resources caused by mine debris flow disasters. This study is based on the theoretical foundations of rainfall automatic identification program, unsteady flow theory, and wavelet threshold denoising theory. It preprocesses key data such as rainfall, groundwater, and surface displacement with the aim of reducing criterion errors and improving the accuracy of determination. By utilizing the underground debris flow warning determination program, warning determination algorithm, and information management system hosted on the monitoring and warning platform, a comprehensive underground debris flow warning system is integrated. This system incorporates determining parameters such as rainfall, water inflow, groundwater level, surface subsidence, pore water pressure, surrounding rock stress, microseismic phenomena, and underground video recognition, with the innovative approach of “weather-surface-underground” multi-directional monitoring. The system was successfully installed and applied in the Pulang Copper Mine in Yunnan Province, demonstrating good application effectiveness. The results indicate that compared to traditional single monitoring methods, the multi-directional monitoring and warning system for underground debris flows has advantages such as low fault tolerance and high accuracy, making it more suitable for ensuring safe mining in mining areas. Full article

The shear factor of ore drawing is an important factor affecting the formation of underground debris flows. The aim of this study was to investigate the effect of the mining shear factor on underground debris flows in natural caving. The research background was the underground debris flow in the Plan copper mine, and we analyzed the characteristics of the slurry material structure of the underground debris flow, as well as the influence of the ore-drawing shear factor on the formation mechanism of the underground debris flow. The results showed that the slurry of the underground debris flow in the Plan mine is both a pseudoplastic and thixotropic fluid. Shearing force induced in drawing deforms the slurry and decreases its viscosity with the increase in shear rate and time. The shear force produced by the flow of ore particles first produces shear action on the paste in the shear boundary region of the ore drawing, reducing the paste viscosity while increasing its fluidity. Consequently, the “activation” makes the paste flowable, which flows along with the bulk ore flowing through the drawing mouth. The continuous ore-drawing process continuously shears the new moraine slurry in the ore-drawing channel and continuously “activates” the moraine slurry in the ore-drawing channel. Finally, destructive underground debris flow accident of a certain scale occurs. To our knowledge, this study thoroughly investigated the effect of the ore-drawing shear factor on the formation mechanism of underground debris flows, which not only broadens the research field of debris flow but also covers the deficiency of systematic research on underground debris flows, providing theoretical guidance for the prevention and control of underground debris flows. Full article

The performance of flow through orifices on a perforated distribution pipe between periods with and without partial clogging (submersion of part of the distribution pipe) was compared. The distribution pipe receives runoff and delivers it to an underground infiltration bed. Clogging appeared in winter but was reduced in summer. Performance of flow delivery was found to be defined by the effective pipe length and the pressure head. ANCOVA (ANalysis of COVAriance) was used to examine the clogging effect with flow rate plotted against the effective pipe length times the square root of the mean pressure head, and found that it was significant during low or no rainfall. During larger storms, clogging had little effect on pipe performance. Clogging might be caused by leaves and other trash accumulating in the lower section of the pipe in winter and its effect was insignificant when the water level rose in the pipe, utilizing significantly more orifices on the distribution pipe. Larger storms might also move the debris, thus exposing the orifices. The current maintenance schedule was sufficient to keep the distribution pipe at a satisfactory performance even though partial clogging can exist. Full article

The stability of underground openings is pivotal to sustainable safe mining in underground coal mines. To determine the stability and tunneling safety issues in 800-m-deep underground openings through large fault zones in argillaceous rocks in the Guqiao Coal Mine in East China, the pilot industrial test, laboratory experimentation, and field measurements were used to analyze the large deformations and failure characteristics of the surrounding rock, the influence factors of safe excavation and stability of underground openings, and to study the stability control countermeasures. The main factors influencing the stability and tunneling safety include large fault zones, high in situ stress, poor mechanical properties and engineering performance of the argillaceous rock mass, groundwater inrush and gas outburst. According to the field study, the anchor-ability of cables and the groutability of cement-matrix materials in the argillaceous rock in the large fault zones were extremely poor, and deformations and failure of the surrounding rock were characterized by dramatic initial deformation, high long-term creep rate, obviously asymmetric deformations and failure, rebound of roof displacements, overall loosened deformations of deep surrounding rock on a large scale, and high sensitivity to engineering disturbance and water immersion. Various geo-hazards occurred during the pilot excavation, including roof collapse, groundwater inrush, and debris flow. Control techniques are proposed and should be adopted to ensure tunneling safety and to control the stability of deep underground openings through large fault zones, including regional strata reinforcement technique such as ground surface pre-grouting, primary enhanced control measures, floor grouting reinforcement technique, and secondary enclosed support measures for long-term stability, which are critical for ensuring the sustainable development of the coal mine. Full article