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Hazards of Environmental Disruption in Mine Goafs and Stability Evaluation in Gaofeng Mining Area
China is rich in mineral resources with many points and broad faces in metal and nonmetal mines. However, numerous goafs are formed due to backward mining technology, low intensification degree, incomplete safety precautions, and the excessive exploitation of mineral resources, thus leading to severe environmental disruption. Accidents, like goaf collapse, are major geological disasters in mine production, and goaf stability evaluation is of great importance for reducing natural disasters in goafs and implementing environmental protection. The hazard types of environmental disruption caused by mine goafs were first analyzed in this study. Then, an influence factor index system of goaf stability was established, and a case study of a mine goaf in Henan Province was conducted using an analytic hierarchy process (AHP)-based fuzzy comprehensive evaluation model. Results show that the hazards of environmental disruption in mine goafs are manifested in the structural failure of surrounding buildings, massive water and soil loss, the exhaustion of water resources, the degradation of soil quality, and the remarkable reduction of overlying animals and plants. Technical factors exert the maximum influence on underground goaf stability with the total weight value reaching 72.42%, and the influence weight of goaf span on goaf stability reaches 21.43%, followed by goaf area and pillar distribution with influence weights of 18.58% and 11.17%, respectively. Through fuzzy AHP-based comprehensive evaluation and calculation, the goaf stability of the Henan Sandaozhuang open-pit mine in the case study belongs to grade (ordinary), that is, the goaf stability is in the ordinary state, and the evaluation result reflects the reality. The study results have improved the reasonable stability and safety management scheme for complex multi-layer goaf and solved complex goaf hazards faced by Gaofeng mining area, so they will be of general significance for the environmental governance of other underground mine goafs.
Journal Article
Comprehensive Review of Short-Term Voltage Stability Evaluation Methods in Modern Power Systems
The possibility to monitor and evaluate power system stability in real-time is in growing demand. Whilst most stability-related studies focus on long-term voltage stability and frequency stability, very little attention is given to the issue of short-term (voltage) instability. In this paper, the most common evaluation methods present in the literature are summarized, with a focus on their applicability to modern power systems with a large amount of renewable energy integration. The paper presents a first-of-a-kind structured review of this topic. We find that all existing methods have noteworthy limitations that necessitate further improvements. Additionally, the need of having an inclusive short-term instability prediction method is demonstrated, due to strong interactions between various short-term instability mechanisms. These findings provide a good foundation for further research and advancement in the field of real-time stability monitoring.
Journal Article
The Fat Tail
As Ian Bremmer and Preston Keat reveal in this innovative book, volatile political events such as the 2008 Georgia-Russia confrontation--and their catastrophic effects on business--happen much more frequently than investors imagine. On the curve that charts both the frequency of these events and the power of their impact, the \"tail\" of extreme political instability is not reassuringly thin but dangerously fat. Featuring a new Foreward that accounts for the cataclysmic effects of the 2008 financial crisis, The Fat Tail is the first book to both identify the wide range of political ris
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Scaled model tests on pile types influencing the stability of stiffened deep mixed pile-supported embankment over soft clay
Stiffened deep mixed (SDM) piles can be classified into three types based on the relative lengths of the core pile and the outer DM pile: the length of the core pile is shorter than, equal to, or longer than that of the outer DM pile. Limited research has been undertaken to investigate the performance of embankments supported by various types of SDM piles over soft soil. This study carried out a series of model tests to investigate the stability of embankment over soft clay improved by different types of SDM piles. The test results indicated that the improvement factors for embankment stability were 1.37, 1.87, and 1.75 for the tests with short-core, equal-core and long-core SDM piles, respectively. Significant vertical stress was concentrated onto the core pile due to its high stiffness, while the outer DM pile yielded earlier. Under the embankment crest, SDM piles generally failed by compression, while the short-core SDM pile exhibited bulging beneath the core pile tips, and the long-core SDM pile fractured at the unwrapped section. The SDM piles under the embankment slope mainly bore bending moments, and the type of SDM piles affected the bending pattern. The stability of SDM pile-supported embankments can be reasonably evaluated by considering the resisting moment of the piles due to lateral force. The position parameter of equivalent lateral force in an SDM pile-supported embankment ranges from 1/4 to 2/5.
Journal Article
The stability issue of fractured rock mass slope under the influences of freeze–thaw cycle
Freeze–thaw failure of frozen rock slope often occurs during engineering construction and mining in cold area, which poses a great threat to engineering construction and people's life safety. The properties of rock mass in cold region will change with the periodic change of temperature, which makes it difficult to accurately evaluate the stability of slope under the action of freeze–thaw cycle by conventional methods. Based on field investigation and literature review, this paper discusses the characteristics of frozen rock mass and the failure mechanism of frozen rock slope, and gives the types and failure modes of frozen rock slope. Then, the research status of frozen rock slope is analyzed. It is pointed out that the failure of frozen rock slope is the result of thermo-hydro-mechanical (THM) coupling. It is considered that freeze–thaw cycle, rainfall infiltration and fracture propagation have significant effects on the stability of frozen rock slope, and numerical simulation is used to demonstrate. The research shows that the safety factor of frozen rock slope changes dynamically with the surface temperature, and the safety factor of slope decreases year by year with the increase of freeze–thaw cycles, and the fracture expansion will significantly reduce the safety factor. Based on the above knowledge, a time-varying evaluation method of frozen rock slope stability based on THM coupling theory is proposed. This paper can deepen scholars' understanding of rock fracture slope in cold area and promote related research work.
Journal Article
Instability mechanism of loess-mudstone landslides under rainfall infiltration conditions
The evolution of seepage field in large loess-mudstone landslides is significantly influenced by rainfall infiltration, which is a critical factor affecting their stability. This paper presented a case study of the Hongya Village landslide in Huzhu County, Qinghai Province, to better understand the impact of rainfall infiltration on the triggering mechanism of loess-mudstone landslides. A combination of field investigations, high-density electrical resistivity surveys, and numerical simulations was employed to systematically analyze the temporal and spatial distribution of pore water pressure, volumetric water content, and shear strain within the landslide mass under rainfall infiltration conditions. The results indicated that the rainfall infiltration markedly alters the seepage characteristics of the landslide mass, leading to a sharp increase in pore water pressure and a significant reduction in shear strength, which consequently reduced the overall stability of the landslide. The stability analysis identified a stepwise instability process in the landslide, characterized by “shear displacement-tensile failure-pulling effect” triggered by rainfall infiltration. The findings provide a comprehensive understanding of the instability mechanisms of loess-mudstone landslides under rainfall conditions, thereby offering valuable scientific guidance and technical support for the prevention and mitigation of similar landslide hazards.
Journal Article
Stability evaluation of underground gas storage salt caverns with micro-leakage interlayer in bedded rock salt of Jintan, China
Recent in situ pressure test indicates that there is a mudstone interlayer with high permeability in the open hole of the underground gas storage (UGS) salt caverns in Jintan, China. The interlayer is called the “micro-leakage interlayer (MLI).” MLI brings a great new challenge for UGSs construction and operation. The stability evaluation is the main research target of this paper. Laboratory tests have been carried out on samples collected from the target formation to determine the mechanical properties. A 3D geomechanical model of the two adjacent caverns with MLI is established based on the geological data and the laboratory test results. The minimum and maximum limit operating pressures are determined as 6 MPa and 18 MPa based on the numerical simulation results of six operating conditions. Two operating conditions (synchronous and asynchronous injection–production) are designed and discussed. The result shows that the MLI has little effect on the stability of the caverns and can be ignored. The stability under the two operating conditions is quite good, suggesting that asynchronous injection–production can be used in the actual operation. This makes the operation more flexible to meet unpredictable situations. The tightness analysis under the two operating conditions will be the subject of future investigations.
Journal Article
Stability Analysis of a Typical Salt Cavern Gas Storage in the Jintan Area of China
Using underground space to store natural gas resources is an important means by which to solve emergency peak shaving of natural gas. Rock salt gas storage is widely recognized due to its high-efficiency peak shaving and environmental protection. Damage and stress concentrations inside the cavern injection during withdrawal operations and throughout the storage facility life have always been among the most important safety issues. Therefore, accurate evaluation of the stability of rock salt gas storage during operation is of paramount significance to field management and safety control. In this study, we used the finite element numerical analysis software Flac3D to numerically simulate large displacement deformations of the cavern wall during gas storage—in addition to the distribution of the plastic zone of the rock around the cavern and the surface settlement—under different working conditions. We found that the maximum surface settlement value occurred near the upper part of the cavern. The surface settlement value increased as a function of creep time, but this increase leveled off, that is, a convergence trend was observed. The value was relatively small and, therefore, had little impact on the surface. The application of gas pressure inhibited the growth of the plastic zone, but on the whole, the plastic zone’s range increased proportionally to creep time. For the 20-year creep condition, the deformation value of the cavern’s surrounding rock was large. Combined with the distribution of the plastic zone, we believe that the cavern’s surrounding rock is unstable; thus, corresponding reinforcement measures must be taken.
Journal Article
Evaluation of Slope Stability within the Influence of Mining Based on Combined Weighting and Finite Cloud Model
Coal mining under slopes often leads to slope instability, resulting in substantial economic losses and human casualties. Therefore, constructing a scientific and practical slope stability evaluation model for slope disaster prevention and control is of great significance. In this study, seven evaluation indexes were selected, and their influence mechanisms were analyzed to establish a system of evaluation indexes for the stability of mining slopes in Xing County, Shanxi Province, China. A new evaluation model for the stability of mining slopes was established based on the interval analytic hierarchy process (IAHP) to determine the subjective weights of the indexes and the improved CRITIC method to determine the objective weights of the indexes, which circumvented the limitations of subjective or objective weights by combining the minimum discriminating information. The model was applied to the mining slopes in Xing County, Shanxi Province, and the results showed that slopes A, C, D and E were in an unstable state, slope B was in an understable state after mining. Finally, the accuracy of the evaluation results was verified through field surveys. The model has engineering application value in predicting the stability of mining slopes and can provide theoretical suggestions for later slope management to ensure the safe production of coal mines.
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