Monitoring the Characteristics of Ecological Cumulative Effect Due to Mining Disturbance Utilizing Remote Sensing

This study conducted land cover classification and inversion analysis to estimate land surface temperature, soil moisture, specific humidity, atmospheric water vapor density, and relative humidity using remote sensing and multi-source mining data. Using 1990–2020 data from the Shendong mining area in Inner Mongolia, China, the eco-environmental evolution and the ecological cumulative effects (ECE) of mining operations were characterized and analyzed at a long-term scale. The results show that while the eco-environment was generally stable, mining activities affected the eco-environment at the initial stage (1990–2000) to a certain degree. During the rapid development stage of coal mining, the eco-environment was severely damaged, and the ECE were significant at the temporal scale. The absolute value of the change rate of ecological parameters was increasing. Due to an increased focus on ecological restoration, starting in 2010, the environmental indicators gradually stabilized and the eco-environment improved considerably, ushering in a period of stability for coal mining activities. The absolute value of the change rate of ecological parameters became stable. Analysis of the change in eco-environmental indicators with distance and comparison to the contrast area showed the ECE characteristics from mining disturbance at the spatial scale. This study shows that remote sensing technology can be used to characterize the ECE from mining operations and analyze eco-environmental indicators, providing crucial information in support of ecological protection and restoration, particularly in coal mining areas.

The Stability of Roadway Groups under Rheology Coupling Mining Disturbance

The deep roadway groups play an important role in transportation and ventilation in coal mine production. Therefore, it is very important to comprehensively analyze the coupling effect of rheological deformation and coal mining on the stability of the roadway groups. In this paper, the disturbance effects of different stop-mining lines on roadway groups under long-term rheology were investigated by numerical simulation, and the failure mechanism of roadway groups with large sections and multiple disturbances in a deep well was revealed. The results show that the long working face will lead to the collapse of key strata, and the influence range will spread to the adjacent roadway groups. When the distance between the working face and the stop-mining line is 100 m, the roadway groups cannot be affected by the working face mining, and the reserved width of the coal pillar can be determined to be 100 m, which increases the stability of the roadway’s surrounding rock and maintains the mine safety production. This paper aims to provide a reference for groups design and control under similar conditions.

Continuous Detection of Surface-Mining Footprint in Copper Mine Using Google Earth Engine

Socioeconomic development is often dependent on the production of mining resources, but both opencast and underground mining harm vegetation and the eco-environment. Under the requirements of the construction for ecological civilization in China, more attention has been paid to the reclamation of mines and mining management. Thus, it is the basement of formulating policies related to mining management and implementing reclamation that detection of mining disturbance rapidly and accurately. This research carries on an empirical study in the Dexing copper mine, Jiangxi, China, aiming at exploring the process of distance and reclamation. Based on the dense time-series stack derived from the Landsat archive on Google Earth Engine (GEE), the disturbance of surface mining in the 1986–2020 period has been detected using the continuous change detection and classification (CCDC) algorithm. The results are that: (1) the overall accuracy of damage and recovery is 92% and 88%, respectively, and the Kappa coefficient is 85% and 84% respectively. This means that we obtained an ideal detection effect; (2) the surface-mining area was increasing from 1986–2020 in the Dexing copper mine, and the accumulation of mining damage is approximately 2865.96 ha with an annual area of 81.88 ha. We also found that the area was fluctuating with the increase. The detected natural restoration was appraised at a total of 544.95 ha in the 1988–2020 period with an average restoration of 16.03 ha. This means that it just restores less in general; (3) it has always been the case that the Dexing mine is damaged by mining and reclamation in the whole year (it is most frequently damaged month is July). All imageries in the mine are detected by the CCDC algorithm, and they are classified as four types by disturbing number in pixel scale (i.e., 0, 1, 2, more than 2 times). Based on that, we found that the only once disturbed pixels account for 64.75% of the whole disturbed pixels, which is the majority in the four classes; (4) this method provides an innovative perspective for obtaining the mining disturbed dynamic information timely and accurately and ensures that the time and number of surface mining disturbed areas are identified accurately. This method is also valuable in other applications including the detection of other similar regions.

Stability Analysis of Roadway Groups under Multi-Mining Disturbances

The roadway stability has been regarded as the main challenging issue for safety and productivity of deep underground coal mines, particularly where roadways are affected by coal mining activities. This study investigates the −740 m main roadway in the Jining No. 2 Coal Mine to provide a theoretical basis for the stability control of the main deep roadway affected by disturbances of adjacent working activities. Field surveys, theoretical analyses, and numerical simulations are used to reveal mechanisms of the coal mining disturbance. The field survey shows that the deformation of roadway increases when the work face advances near the roadway group. Long working face mining causes the key strata to collapse based on the key strata theory and then disturbs the adjacent roadway group. When the working face is 100 m away from the stop-mining line, the roadway group is affected by the mining face, and the width roadway protection coal pillar is determined to be about 100 m. Flac3D simulations prove the accuracy of the theoretical result. Through reinforcement and support measures for the main roadway, the overall strength of the surrounding rock is enhanced, the stability of the surrounding rock of the roadway is guaranteed, and the safe production of the mine is maintained.

Estimation and verification of fractional derivative-based permeability of coals considering mining-induced stresses

To overcome the inaccuracy of the traditional transient pulse test, a new fractional derivative-based permeability estimation formula based on the transient pulse test is proposed to describe the pressure difference decay of a coal body subjected to mining-induced stresses. The permeability of coal specimens under mining disturbance conditions is measured using the MTS815 rock mechanics test system. The experimental results show that the transient pulse test based on the fractional derivative model provides a much better estimation of the coal specimen’s permeability than the conventional exponential decay model. Analyzing the evolution of the coal’s permeability shows that the permeability tends to decrease in the pre-peak compaction stage, following which it gradually increases in the plastic phase, and then increases sharply in the post-peak phase. The significance of the fractional derivative order γ is discussed, and its analysis shows that the solid-liquid interaction inside the specimen becomes complicated when the stress within the coal specimen changes.

Detection and Characterization of Active Landslides with Multisource SAR Data and Remote Sensing in Western Guizhou, China

The western part of Guizhou is located in the second step of East Asia. Although the area is stratigraphically continuous and the surface is dominated by hard limestone and sandstone, catastrophic landslides often occur, seriously threatening residents' lives and the safety of property. Accurate identification of landslides and analysis of their developmental patterns are vital to prevent and reduce the threat of geological disasters. No active landslide survey data cover this region, so this paper identifies the active landslides in the western part of Guizhou by combining surface deformation information, multitemporal optical remote sensing images, geological lithology, and geomorphic features to obtain deformation information from multisource synthetic aperture radar surface data. This process increases the accuracy and reliability of identifying unstable slopes in areas with dense vegetation and steep terrain. By processing 283 Sentinel-1 and PALSAR-2 synthetic aperture radar data, 588 active landslides, 18 of which are high-risk large-scale landslides (landslide groups), are delineated for the first time in a range of 4.64x104 km2 in the study area. The active landslides mainly include resurrected ancient landslides, reservoir/riverbank landslides, and mining-induced landslides, accounting for 2.4%, 4.1%, and 91.8%, respectively. The spatial distribution of landslides is banded along the cuesta at the edge of an outcrop of coal strata. Landslides are mainly distributed at elevations of 1800–2000 m, with an elevation difference of 50 ~ 100 m and a slope range of 35°~40°. The landslides are characterized by steep slopes, small scales, mass occurrences, and no dominant slope direction, classifying them as cuesta landslides induced by mining disturbance. Furthermore, nuanced remote sensing interpretation of the disaster elements, such as cuesta cliff, tensile cracks, deep and sizeable tensile channels, isolated rock masses, and collapse debris, and their processes of change, reveals that coal mining-disturbed landslides in this region have experienced four primary stages: natural unloading, mining disturbance, displacement acceleration, and slope failure. This is of great significance for understanding the genetic mechanism and developmental patterns, as well as the risk assessment, of this region.

Fracture Propagation and Hydraulic Properties of a Coal Floor Subjected to Thick-Seam Longwalling above a Highly Confined Aquifer

The high-pressure and water-rich confined aquifer occurring in the Ordovician limestone sequence poses great threats to the routine production of underground longwall mining. Considering the intense cooperation of mining disturbance and water pressure, water-conducting fractures within a coal seam floor can connect the lower aquifer and upper goaf, and this hydraulic behavior is considered the root of water inrush hazard and water loss or contamination. In this paper, the panel 4301 of the Longquan coal mine serves as the case where the panel works closely above the floor with high water pressure. By the combination of physical and numerical modelling approaches, the variation characteristics of fracture development and volumetric strain of floor rocks subjected to mining disturbance are analyzed. A numerical computation model is constructed based on the volumetric strain-permeability equation obtained by curve fitting, and on such basis, the impacts of different mining parameters on floor rock permeability are studied. The results show that the floor rocks experience fracture generation, extension, and convergence procedures as the workface advances along the longitudinal direction, and fractures appearing in front of the workface are more developed. In the whole process of coal seam extraction, the volumetric strain profile exhibits “Λ” shape and an inverted saddle shape before and after overburden strata collapse. By controlling a single variable, the paper reveals that panel height is of greater impact on floor permeability changes than panel length and panel width.

Study on Broken Floor Rock Mass by Mining Underground Pressure

As the dangerous level of floor water inrush in Chinese coal field is becoming more and more serious annually, the widely used formulas of broken floor rock mass are belonged to nonlinear type or empirical type. However, they are not well conformed to the practical situation and including mining underground pressure. The biggest depth of broken floor rock mass and the length of gob-floor or mining-floor until the maximum broken floor location are expressed by theoretical formulas on integrity theory. Taking a mining face in Chinese Anhui Province as the object, the relationship between broken floor rock mass and mining underground pressure is studied by numerical simulation, the theoretical analysis, and the DC exploration. The peak and scope of broken floor rock mass will enlarge until reaching limit value with the increasingly advanced distance. The mining gob stress contour is saddle-shaped, and its growing speed is becoming slower, so the 180 m coal mining face has reached the sufficient mining stage. Wave velocity of broken floor rock mass from 0 m to 16 m is greatly decreased by the mining disturbance, and it is basically conformed to theoretical formula and practical situation. The results can be relatively better used in the pressure mining of the Ordovician limestone, because it can provide some safe guarantee for mining deep coal seam.

Analysis of Failure Mechanism of Roadway Surrounding Rock under Thick Coal Seam Strong Mining Disturbance

Severe dynamic disturbance in extrathick coal seam mining has become one of the main factors threatening the stability of roadway surrounding rock. In this article, the #6 thick coal seam of Buliangou mine in Inner Mongolia, China, is taken as the engineering background. A mechanical model of the roadway roof structure is established to obtain an analytic formula of the key block subsidence. A three-dimensional discrete element model is established and used to verify the field measurement results. The fracture characteristics of the main roof above the F6104 transport roadway and the deformation and damage evolution law of the surrounding rock during thick coal seam mining are analyzed. The results show that because of the long-term breaking and falling of the roof rocks during extrathick coal seam mining, the F6104 transport roadway will undergo two severe mining disturbances at the locations of 10∼30 m and 50∼70 m ahead of the F6103 working face. During the two disturbance periods, the roadway roof displacement settles to 300∼350 mm and 750∼800 mm, and the deformation of the solid coal wall reaches 650∼700 mm and 1350∼1450 mm, respectively. The energy change curve of the total length of the fractured key roof is obtained, and when mining at 50 m, the basic roof is close to its tensile strength, and the strain energy can reach the peak value of 5.2 × 10 4 kJ, which easily leads to rock burst. The plastic damage zones on both sides of the roadway develop to the roof central area and eventually coalesce, and the deformation of the surrounding rock is obvious. When mining at 50∼70 m, the basic roof breaks and unloads, and elastic strain energy of 3.57 × 10 4 kJ is instantaneously released. These two dynamic disturbances are the main reasons for the instability of the roadway surrounding rock. The results clarify that the failure mechanism investigation of roadways in thick coal seam mining conditions can be effectively applied to control the stability of the roadway surrounding rock under strong mining disturbance.