Overburden Failure Research Articles

Influence of different mining locations on deformation characteristics of overlying strata on gently anti-dip high-steep mining slope.

High-steep gently inclined mining slopes, prevalent globally, often suffer significant deformation, leading to landslides due to numerous goafs. This research investigates the critical role of goaf location in controlling deformation, failure mechanisms, and disaster evolution, vital for safe mining practices. Through field investigations and model generalization in Guizhou, a physical model test method was used to study three positions of goafs: under the shoulder and foot of the slope, under the slope shoulder, and within the slope. Findings highlight the stronger influence of the goaf's mutual position with the slope shoulder on slope and overburden deformation and failure compared to the slope toe. Deformation and failure modes evolve from collapse toppling to collapse slip and collapse settlement as the goaf shifts from the near slope surface to inside of the slope. Statistical analysis of fracture distribution in the goaf's overlying strata reveals damage increase with larger goafs, following a Gaussian distribution, with concentrated damage in the middle. The study identifies the maximum damage area, influenced by the horizontal distance between the goaf center and slope shoulder. These insights advance understanding of overburden rock deformation in gently inclined high-steep mining slopes.

Prediction of Overburden Failure on the Working Face Using Self-Formed Roadway Mining Technology without Coal Pillars Based on Microseismic Monitoring: A Case Study

Prediction of Overburden Failure on the Working Face Using Self-Formed Roadway Mining Technology without Coal Pillars Based on Microseismic Monitoring: A Case Study

Study on Numerical Simulation of Overburden Failure Height in Stratified Full-Mechanized Caving of Extremely Thick Coal Seam

Study on Numerical Simulation of Overburden Failure Height in Stratified Full-Mechanized Caving of Extremely Thick Coal Seam

Characteristics and Laws of Overburden Failure Caused by Repeated Mining of Multi Coal Seams

With the depletion of coal resources, people began to mine deeper coal resources. In response to the special geological conditions of multiple coal seams, scientific and safe mining of deep coal seams has great practical significance and value. This article analyzes and studies the characteristics and laws of overburden failure caused by multi coal seam mining through physical simulation experiments in Majiazhuang coal mine with multiple coal seam occurrence conditions. The research results indicate that the failure of the overlying rock exhibits a "two zone" characteristic, that is, only the collapse zone and. The mining of multiple coal seams in overburden fracture zones will penetrate to the surface, disrupting groundwater circulation. Different mining thicknesses lead to different heights of overlying rock failure, and the greater the thickness of coal seam mining, the greater the height of overburden failure. The height of overburden damage caused by the mining process of the 15th coal seam runs through each coal seam and goaf to guide the surface.

Green coal mining under buildings by overburden grout injection for coalmine sustainable development of central China

Coal will occupy the main position in China's energy structure for a long time, and the negative externalities of its exploitation have a serious impact on the ground surface and its appurtenances. With the proposal of the dual carbon strategy, the coal-based energy determines that green and safe coal mining should be the priority direction of China's energy development. Taking Xinyi coalmine, which is mined in unstable coal seams with large mining depth, as the research area, the surface response characteristic and subsidence law under the different mining degrees were clarified. Meanwhile, the damage mechanism of buildings was revealed, which was from no obvious damage to Grade Ⅳ under the extremely insufficient mining to subcritical mining. Based on the sustainable development and green production in coalmines, the overburden grout injection technique under buildings that does not affect the normal production was proposed, and its technical principle was described. A weighted grey relational analysis model was established, and obtained that the panel width was the main factor affecting the overburden failure height under subcritical mining. According to the definition of overburden failure degree proposed by the author, the feasibility of overburden grout injection technique under buildings was analyzed and the key parameters, such as slurry diffusion radius, borehole position and depth, grouting system and technology, were determined and successfully applied. The engineering application shows that the maximum surface subsidence after grouting is 253 mm, and the building damage is within the Grade I. Meanwhile, 5.82 Mt of coal resources under the buildings have been liberated, which realizes high quality coal mining, low environmental damage, green and low-carbon, and also provides a reference for the sustainable development of coal enterprises, especially for the exhausted coalmines that recover coal pillars.

Overburden Failure and Ground Pressure Behaviour of Longwall Top Coal Caving in Hard Multi-Layered Roof

Overburden Failure and Ground Pressure Behaviour of Longwall Top Coal Caving in Hard Multi-Layered Roof

Research on a Space-Time Continuous Sensing System for Overburden Deformation and Failure during Coal Mining.

Underground coal mining can cause the deformation, failure, and collapse of the overlying rock mass of a coal seam. If the mining design, monitoring, early warning, or emergency disposal are improper, in that case, it can often lead to mining disasters such as roof falls, water inrush, surface collapse, and ground fissures, seriously threatening the safety of mine engineering and the geological environment protection in mining areas. To ensure the intrinsic security of the entire coal mining process, aspace-time continuous sensing system of overburden deformation and failure was developed, which breaks through the limitations of traditional monitoring methods that characterize the evolution process of overlying rock deformation and ground subsidence. This paper summarizes the classification of typical overburden deformation and failure modes. It researches the space-time continuous sensing of rock-soil mass above the coal seam based on Distributed Fiber Optic Sensing (DFOS). A multi-range strain optical fiber sensing neural series from micron to meter was developed to achieve synchronous sensing of overburden separation, internal micro-cracks, and large rock mass deformation. The sensing cable-rock mass coupling test verified the reliability of the optical fiber monitoring data. The sensing neural network of overburden deformation was constructed using integrated optical fiber layout technology on the ground and underground. Different sensing nerves' performance and application effects in overburden deformation and failure monitoring were compared and analyzed with field monitoring examples. A physical model was used to carry out the experimental study on the overburden subsidence prediction during coal mining. The results showed that the optical fiber monitoring data were reliable and could be used to predict overburden subsidence. The reliability of the calculation model for overlying rock subsidence based on space-time continuous optical fiber sensing data was verified in the application of mining subsidence evaluation. A systematic review of the shortcomings of current overburden deformation observation technology during coal mining was conducted, and a space-time continuous sensing system for overburden deformation and failure was proposed. This system integrated sensing, transmission, processing, early warning, decision-making, and emergency response. Based on the fusion of multi-parameter sensing, multi-method transmission, multi-algorithm processing, and multi-threshold early warning, the system realized the real-time acquisition of space-time continuous information for the overburden above coal seams. This system utilizes long-term historical monitoring data from the research area for data mining and modeling, realizing the prediction and evaluation of the evolution process of overburden deformation as well as the potential for mining subsidence. This work provides a theoretical reference for the prevention and control of mining disasters and the environmental carrying capacity evaluation of coal development.

Reasonable Working-Face Size Based on Full Mining of Overburden Failure

To improve production efficiency and prevent potential disasters in coal mines, comprehensive research methods such as similar simulation, numerical simulation, theoretical analysis, and on-site detection were used in this study. The migration characteristics of overburden rock under different working face lengths and development heights of water-conducting fracture zones were investigated via these methods in order to determine the reasonable length of the working face. The results show that the regularity of the development height of water-conducting fracture zones in similar simulations and numerical simulations is highly consistent, and the final stable values are 48 and 50 m. When the working face length was 300 m, the error between the simulated value and the value calculated from the formula dropped below 10% and exhibited a further decreasing trend; as a result, the working face length of 300 m was found to be the turning point for the development height of the water-conducting fracture zone to become stable. Based on the simulation results and mining damage theory, the critical size of the working face was 307.6 m, and the height of the water-conducting fracture zone was determined to be in the range of 45.5–60.5 m. The actual detection result of the height of the water-conducting fracture zone under the critical size of the working face was 55 m, which conforms to the law obtained from the simulation. Finally, the reasonable working face length under the geological conditions of a coal mine was determined to be 300–400 m. This study offers important reference value for determining the reasonable working face length under similar geological conditions, and may have significance for the sustainable development of coal resource mining.

Evolution of overburden fracture and water seepage in coal seam group mining an example in Lingxin coal mine

Taking Lingxin Coal Mine as the research object, the combination of physical experiment and numerical simulation analysis was used to study the mining failure of overlying strata and the development of surrounding rock cracks in goaf. The results show that when the underground coal seam mining is not sufficient, the overburden separation is developed, the connected pore area of the overburden failure accounts for about 20% of the total mining area. When the underground coal seam is fully mined, the overburden failure is severe, the overburden failure cracks are interconnected, and the connected pore area increases significantly.

Overburden Failure Associated with Slicing Mining in a Super Thick Coal Seam under Special Weak Aquifers

With the increasing improvement of national ecological standards, the eco-environmental problems caused by super thick coal seam mining in western China are becoming more and more serious. The failure law of weak overburden stratum is an important factor affecting the safe mining of coal. The failure characteristics of weakly cemented overburden under high-intensity mining in the mining area of western China were studied. For this purpose, a case study was conducted in the 1101 working face of the Baituyao Coal Mine in Ürümqi County. Based on the analysis of geological conditions in the study area, we combined empirical calculations with engineering analogy, physical simulation, and numerical simulation to comprehensively analyze the characteristics of mining-induced overburden failure. The study showed that the overburden in the study area had several unfavorable engineering geological characteristics, including ease of softening in the presence of water. The Middle Jurassic Xishanyao Formation is a directly recharged aquifer with a weak water-retaining property. Overburden failure mainly occurred at the two ends of the open-off cut. During the mining process, vertical fissures and bed-separated fissures were periodically developed and closed, and the fissures were interconnected. The overburden was fractured, and the fractured zone showed a trapezoidal shape, tapering off from bottom to top. The heights of the caving zone and the water-conducting fracture zone were 25 and 280 m, respectively, in the 1101 working face of the Baituyao Coal Mine, and the ratio of fracturing to mining height was 14.0. Due to the weakly cemented overburden and the presence of the Neogene weak aquifer, the risk of water and sand bursts still exists in this working face under high-intensity mining. Our findings shed light on the safe mining and environmental protection of the ground surface in coal mine shafts in western China.

A method for determining the overburden failure height of coal mining based on the change of drilling speed and the leakage of sectional water injection in underground upward bolehole

A coal mine in Xinjiang was taken as research site in this paper, it is proposed to determine the overburden failure height based on both the drilling speed of upward bolehole and sectional water injection methods. The results show that the overburden failure height of borehole CH01 is 44.80m based on the drilling speed and 44.32m based on the sectional water injection method respectively, with the difference 0.48m; also the results of borehole CH02 is 42.58m and 40.59m respectively, with the difference 1.99m.The overburden failure height determined based on the drilling speed is basically the same as the results aquired by the sectional water injection method. The latter validates the former's accuracy. So the overburden failure height of mining based on the drilling speed in underground upward borehole has good accuracy, also the height of caving zone can be aquired by this method. Both of the methods verified each other, and provides a new way for field measurement of overburden failure height in coal mines.

Research on Overburden Failure Characteristics Based on the Theory of Plates and Shells

To reveal the overburden failure characteristics during backfill mining, theoretical analysis based on the theory of plates and shells and field measurements were combined. Based on the theory of plates and shells, a mechanical model for the overburden failure mechanism during backfill mining was established, through which the fracture conditions of overburden during backfill mining were judged. By analyzing the fracture process and revealing the fracture mechanism, the fractured zone in overburden during backfill mining was found not to develop uniformly, but changed in a leaping manner. Field measurement was conducted taking the 1327 working face in Xima Coal Mine (Shenyang City, Liaoning Province, China) as an example to monitor and analyze the roof-to-floor convergence (RFC), strata behaviors at the working face, and overburden failure during backfill mining. Monitoring results show that the distance between the monitoring points and the working face was highly consistent with the periodic weighting interval when the RFC increased in a leaping manner; the RFC grew in a leaping manner after each roof weighting, as well as the fractured zone. By monitoring and analyzing overburden failure, it was determined that the maximum height of the fractured zone was 10.7 m and a leaping phenomenon was present in the development process of the fractured zone. The conclusions of theoretical analysis were completely consistent with those of the field measurements, thus confirming the leaping development of the fractured zone in overburden during backfill mining.

Evolution Characteristics of Overburden Instability and Failure under Deep Complex Mining Conditions

Aiming at the problems of intensified deformation and serious stress damage of stope overburden during mining in deep typical geological environment, taking the deep mining face of a mine in the northwest as the research background, the characteristics and influencing factors of overburden collapse in deep geological environment are analyzed, a comprehensive evaluation system affecting overburden instability and deformation is established, and the temporal and spatial evolution law of deep stope roof failure is obtained by using the “three-zone” distribution theory of overburden, analytic hierarchy process, and numerical simulation method. The results show that high ground stress has the most significant impact on the geological environment of deep stope, followed by the properties of surrounding rock, hydrogeological conditions, and unloading disturbance. The damage degree of the plastic zone at the top of the overburden is greater than that at the bottom. With the increase of mining time, the damage range of the roof and floor gradually increases. In the process of coal seam mining, the increasing range and sinking trend of roof stress are larger near the working face, and the farther away from the working face, the increasing range decreases continuously. The research conclusion provides an important reference for coal seam safety mining and surrounding rock control in complex environments such as deep mining, high stress, and strong disturbance.

Calculation of Subsidence due to Longwall Mining with Overburden Grouting and Its Application

This paper presents a prediction method of mining-induced surface subsidence due to longwall mining with overburden grouting, which has been proven an effective method to mitigate the overburden failure. This paper proposes a partial overburden grouting (POG) mining method based on surface subsidence basin inversion and innovative longwall panel layout to mitigate overburden failure and subsidence. A prediction model of surface subsidence with overburden grouting, namely, overburden grouting equivalent calculation model (OGECM), is proposed. In this study, an engineering design process and method of POG was established, the strike and dip excavation length and grouting quantity combined as critical indicators for determining the key parameter in surface basin control. In applications at the field grouting test, the surface subsidence characteristics of POG on the side of the opening line of longwall panel were investigated through surface observation station and estimated surface subsidence reduction ratio based on OGECM with grouting compared with those without. The field measurement validated the new subsidence calculation method. POG technology applied to subsidence control has effectiveness in controlling the surface subsidence to less engineering cost but expanding the applications.

Development Law of Water-Conducting Fracture Zone in the Fully Mechanized Caving Face of Gob-Side Entry Driving: A Case Study

This study is aimed at exploring the influence of narrow coal pillars in gob-side entry driving (GSED) on the development height of the water-conducting fracture zone (WCFZ) in the fully mechanized caving face. In reference to the geological mining conditions of working face 11915 of Gequan (GQ) Coal Mine, the development law of the WCFZ in the GSED fully mechanized caving face was studied by means of formula calculation, on-site measurement, theoretical analysis, and simulation. The research results disclose that the development height of the WCFZ in the GSED fully mechanized caving face is affected by narrow coal pillars of GSED. When the narrow coal pillars lose stability, the overburden failure changes from insufficient mining to sufficient mining, and the WCFZ in the overburden changes from an arch-shaped one to a saddle-shaped one. Additionally, the development height of the WCFZ surges.

Characteristics of Overburden and Ground Failure in Mining of Shallow Buried Thick Coal Seams under Thick Aeolian Sand

Mining can lead to overburden failure and ground damage, which are more severe in mining shallow buried thick coal seams (SBTCS) under thick aeolian sand (TAS). We attempted to discover characteristics of mining in this particular geological condition through theoretical derivation and numerical simulation, and field monitoring. Theoretical methods, combined with numerical simulation and field monitoring methods, reveal the essence of the development and distribution of surface cracks caused by mining SBTCS and depth to thickness ratio (DTR) to be 13.43, less than 15. The findings show that, when mining SBTCS, the overburden breaks down periodically, the initial collapse distance is greater than the collapse step, approximately 55 m on average, and the collapse step is approximately 45 m, on average, in the Daliuta Coal Mine. The collapsed blocks are stacked into goaf and form “masonry beams”, and many cracks and pores are generated between the blocks. The weak stress of the aeolian sand layer causes the movement angle in the aeolian sand layer to be smaller than that in the bedrock, and leads to much sheer, tension and compression failure on the ground, and the main forms of cracks are compression uplift, tensile cracking, shear step.

Study on the Overburden Failure Law of High-Intensity Mining in Gully Areas With Exposed Bedrock

Most hilly areas are dotted with gullies, some of which contain plenty of water, especially in rainy seasons. Once surface water penetrates the underground working face, it will lead to an increased water inflow of the working face. Even worse, it may induce water and sand burst accidents. To prevent geological disasters such as water and sand burst and ensure the safe production in coal mines, it is necessary to reveal the development law of “two zones” in the overburden caused by shallow-seam fully mechanized top coal caving high-intensity mining in hilly areas with exposed bedrock and timely grasp the communication between the water-flowing fractured zone (WFFZ) and the water in surface gullies. In this study, the working face P2 of the exposed bedrock surface in the Coal Mine DN is taken as the research object. First, the characteristics of overburden movement and the law of exposed bedrock surface movement in areas with exposed bedrock were investigated through similar simulation. Meanwhile, the temporal–spatial evolution of overburden movement caused by shallow-seam fully mechanized top coal caving high-intensity mining was clarified, and the mode of overburden movement was revealed. Moreover, the reason why the water inflow of the underground working face increases suddenly was theoretically explained. The following conclusions were drawn: Under shallow-seam fully mechanized top coal caving high-intensity mining, the WFFZ of the working face P2 is directly connected to the exposed bedrock surface, and the movement of the overburden is subject to the typical “two-zone” mode. The development height of the WFFZ is greater than the value in the traditional “three-zone” mode calculated according to the empirical formulas. The ratio of the WFFZ height to the mining thickness is 43.75. Under the “two-zone” mode, a water-flowing channel exists in the overburden near the open-off cut and the stopping line. When the surface water source is in the right position, the water inflow of the underground working face will increase suddenly.

Model Test Study on Overburden Failure and Fracture Evolution Characteristics of Deep Stope with Variable Length

Taking two typical stopes with variable length of working face inclined length from small to large and from large to small as the research object, the stope overburden structure model under different face length conditions is constructed through laboratory similar material simulation test, and the dynamic evolution laws of overburden instability deformation, unloading expansion, and collapse failure of forward and reverse knife handle stopes are analyzed. The three‐dimensional perspective technology of parallel network electrical method is used to study the spatial distribution range and fracture development characteristics of overburden internal failure. The research shows that the overburden fracture of stope with variable length has the “time‐pace‐scale” evolution effect of short‐time sudden change, zoning load transfer, and continuous extension. The evolution of roof fracture has experienced the development process of unloading expansion, tensile fracture instability, shrinkage deformation, and closure stability. The rise and fall of resistivity during mining in stope with variable length is closely related to the mining time step. When mining 40 cm, it is the position where the resistivity value changes suddenly. The rise of resistivity in the vertical direction makes the electric field show the transient response characteristics of dynamic expansion and rapid evolution. The development height of water conducting fracture zone of the reverse knife handle working face with the inclined length changing from large to small is slightly larger, the degree of overburden damage is high, and the fracture development is relatively sufficient.

Characteristics of Overburden Failure and Fracture Evolution in Shallow Buried Working Face with Large Mining Height

In order to solve the issues of uncertain overburden failure height and water loss at the Daliuta coal mine, the collapse characteristics of overburden and the development height of water-conducting fractured zone were studied by using physical modeling, FLAC 3D numerical simulation, and field observation, which were used to verify each other. In order to quantitatively analyze the distribution characteristics of fracture rate of overlying rock mass in goaf, the overburden collapse image was binarized. The results showed that: (1) the failure characteristics of overburden in goaf obtained by the three research methods were roughly consistent, and the reliability of the results was high. The overburden failure height of No. 5−2 coal with large mining height was 137.32–153 m, which was 20.8–23.2 times the mining height. (2) The repeated mining of No. 5−2 coal intensified the further failure of the disturbed rock mass in the No. 2−2 coal goaf. (3) In the horizontal direction of the goaf, the fracture rate of rock mass was distributed in the shape of “saddle”. In the longitudinal direction of the goaf, the rock mass fracture rate decreased in a logarithmic function with the increase of the height from the mining coal seam. Overall, the conclusions are of engineering significance for accurately adopting water resources protection mining technology and reducing mine water inrush disasters.

Research on Structural Evolution and Microseismic Response Characteristics of Overlying Strata during Repeated Mining of Steeply Inclined and Extra Thick Coal Seams

Abstract Repeated mining is the main factor that leads to development, propagation, and eventual deformation of the overlying strata fissures in the steeply inclined and extra thick coal seams (SIETCS). The evolution of the overlying strata structure is closely related to microseismic events in a mine. As the mining depth increases, the evolution rules of the overlying strata structure become more complicated and can easily induce dynamic disaster accidents. To solve these problems, this paper established a physical similarity simulation model. Microseismic monitoring equipment was used to study the relationship between the evolution of the overlying strata structure and the energy-frequency of microseismic events. On the basis of the principle of quantitative seismology, the response relationship between the overlying strata structure and the microseisms at different mining stages was compared and analyzed from a quantitative perspective. The characteristics of cumulative apparent volume, energy index, and microseismic b value were used to reveal the precursor characteristics of overburden instability and failure. The results showed that due to the occurrence characteristics of coal seam, the distribution characteristics of rock stratum stress, and the effects of mining disturbances, the energy accumulation-release period after instability failure of the overlying strata induced by shallow mining was longer than the energy accumulation-release period induced by deep mining. And the deep coal and rock mass had a periodic “balance-instability-rebalance-instability again” dynamic evolution process under the disturbance of repeated mining. In the working face mining, the slope of the accumulative apparent volume ΣVA curve suddenly increased, and the energy index EI gradually decreased at the late peak period, which indicated the deformation and failure of overburden. However, the b value of the microseismic event presented the precursory characteristics of rock stratum fracture that gradually increased and then changed drastically.