Research on prediction method of coal mining surface subsidence based on MMF optimization model.

Coal seam mining causes fracture and movement of overlying strata in goaf, and endangers the safety of surface structures and underground pipelines. Based on the engineering geological conditions of 22,122 working face in Cuncaota No.2 Coal Mine of China Shenhua Shendong Coal Group Co., Ltd. a similar material model test of mining overburden rock was carried out. The subsidence of overburden rock was obtained through the full-section strain data of distributed optical fiber technology, and the characteristics of mining surface subsidence were studied. The Weibull model was used to adjust the mathematical form of the first half of the surface subsidence curve via the MMF function. On this basis, the prediction model of coal seam mining surface subsidence was established, and the parameters of the prediction model of surface subsidence were determined. The test results show that with the advancement of coal seam mining, the fit goodness of the surface subsidence prediction curve based on the MMF optimization model reaches 0.987. Compared with the measured values, the relative error of the surface subsidence prediction model is reduced to less than 10%. The model displays good prediction accuracy. The time required for settlement stability in the prediction model is positively correlated with parameter a and negatively correlated with parameter b. The research results can be further extended to the prediction of overburden "three zones" subsidence, and provide a scientific basis for the evaluation of surface subsidence compression potential in coal mine goaf.

Non-Tectonic Geohazards of Guangdong Province, China, Monitored Using Sentinel-1A/B from 2015 to 2022.

Guangdong Province, home to 21 cities and a permanent population of 127.06 million people, boasts the largest provincial economy in China, contributing 11.76% to the national GDP in 2023. However, it is prone to geological hazards due to its geological conditions, extreme weather, and extensive human activities. Geohazards not only endanger lives but also hinder regional economic development. Monitoring surface deformation regularly can promptly detect geological hazards and allow for effective mitigation strategies. Traditional ground subsidence monitoring methods are insufficient for comprehensive surveys and rapid monitoring of geological hazards in the whole province. Interferometric Synthetic Aperture Radar (InSAR) technology using satellite images can achieve wide-area geohazard monitoring. However, current geological hazard monitoring in Guangdong Province based on InSAR technology lacks regional analysis and statistics of surface deformation across the entire province. Furthermore, such monitoring fails to analyze the spatial-temporal characteristics of surface deformation and disaster evolution mechanisms by considering the local geological features. To address these issues, current work utilizes Sentinel-1A/B satellite data covering Guangdong Province from 2015 to 2022 to obtain the wide-area surface deformation in the whole province using the multi-temporal (MT) InSAR technology. Based on the deformation results, a wide-area deformation region automatic identification method is used to identify the surface deformation regions and count the deformation area in each city of Guangdong Province. By analyzing the results, we obtained the following findings: (1) Using the automatic identification algorithm we identified 2394 deformation regions. (2) Surface subsidence is concentrated in the delta regions and reclamation areas; over a 4 cm/year subsidence rate is observed in the hilly regions of northern Guangdong, particularly in mining areas. (3) Surface deformation is closely related to geological structures and human activities. (4) Sentinel-1 satellite C-band imagery is highly effective for wide-area geological hazard monitoring, but has limitations in monitoring small-area geological hazards. In the future, combining the high-spatial-temporal-resolution L-band imagery from the NISAR satellite with Sentinel-1 imagery will allow for comprehensive monitoring and early warning of geological hazards, achieving multiple geometric and platform perspectives for geological hazard monitoring and management in Guangdong Province. The findings of this study have significant reference value for the monitoring and management of geological disasters in Guangdong Province.

A deep learning-based combination method of spatio-temporal prediction for regional mining surface subsidence.

In coal mining areas, surface subsidence poses significant risks to human life and property. Fortunately, surface subsidence caused by coal mining can be monitored and predicted by using various methods, e.g., probability integral method and deep learning (DL) methods. Although DL methods show promise in predicting subsidence, they often lack accuracy due to insufficient consideration of spatial correlation and temporal nonlinearity. Considering this issue, we propose a novel DL-based approach for predicting mining surface subsidence. Our method employs K-means clustering to partition spatial data, allowing the application of a gate recurrent unit (GRU) model to capture nonlinear relationships in subsidence time series within each partition. Optimization using snake optimization (SO) further enhances model accuracy globally. Validation shows our method outperforms traditional Long Short-Term Memory (LSTM) and GRU models, achieving 99.1% of sample pixels with less than 8 mm absolute error.

Stability analysis of pumped storage hydropower plant in abandoned open-pit mine affected by dynamic surface subsidence of combined mining.

The construction of a pumped storage hydropower plant (PSHP) in an abandoned open-pit mine is a potential alternative to green mining and energy storage, which can increase the utilization rate of renewable energy and develop residual resources of abandoned mines. Dynamic surface subsidence affected by combined underground and open-pit mining (CUOPM) seriously affects the construction and operation of the PSHP and is one of the critical scientific issues that needs to be solved immediately. The stability of the PSHP was analyzed and treatment scheme of the goafs was proposed based on on-site measurement, theoretical analysis, and numerical simulation. First, the distribution of goafs in the Haizhou open-pit mining area was investigated and surface subsidence value was obtained using InSAR technology and ground monitoring. Secondly, the surface subsidence mechanism affected by CUOPM is analyzed and indicates the subsidence maximum values and scope of influence are greater than those of single underground mining. A dynamic surface subsidence prediction model for combined mining is established based on the Knothe time function model. Thirdly, based on the CVISC model, the numerical calculation models were established by using FLAC3D, and the characteristics and laws of surface subsidence in different periods of CUOPM were studied. The comparative analysis of the observation results shows that the proposed model and numerical simulation calculation method have excellent applicability and accuracy. Finally, a stability evaluation method of PSHP was established, and the results of the evaluation show that the affected areas are the semi-ground powerhouse (SGPH) and the west side of the lower reservoir. The method of grouting filling was used to treat the goafs, and the results showed that it effectively alleviates the dynamic surface subsidence affected by CUOPM, and provides a safety guarantee for PSHP.

A design approach of panel size for the cooperative development of cropland protection and coal mining in a coal-cropland overlapping area.

Cropland is the foundation of food security. Coal is the guarantee of energy security. As China's demand for coal and grain continues to increase, so does the overlap area of their production bases. Unrestrained underground mining can cause serious damage to cropland, leading to increasing conflicts between coal mining and food production. Thus, this paper used a partial backfilling mining technology to control surface subsidence and thus protect cropland. The key to successfully implementing the technology is how to design the panel size. However, the design efficiency of the conventional enumeration method is low. Therefore, this paper proposed a design approach based on improved particle swarm optimization. The results indicated that the approach could quickly find the optimal size of the panel compared with the enumeration method and particle swarm optimization. Moreover, if the longwall panel is mined according to the size designed by the approach, the cropland will be protected, and the cost will be reduced. This study can provide technical support for the cooperative development of cropland protection and coal mining in a coal-cropland overlapping area.

Multi-temporal SAR Interferometry (MTInSAR)-based study of surface subsidence and its impact on Krishna Godavari (KG) basin in India: a support vector approach.

The surface subsidence in the Krishna Godavari (KG) basin in India has increased with the discovery of crude oil and natural gas reserves since 1983. With private players coming up to bag the exploration and refining contracts, there must be timely monitoring of the surface subsidence of the region so that remedial measures for the resettlement of the populations can be taken promptly. Regular monitoring is necessary since the region is fertile and any seawater ingress results in the loss of valuable cultivable land. Multi-temporal SAR Interferometry (MTInSAR) technique has been applied successfully all over the world for the study and regular monitoring of land surface subsidence scenarios. This study utilizes data from Sentinel-1 C-band SAR sensor for MTInSAR-based surface subsidence and RADAR Vegetation Index (RVI)-based vegetation loss for the same season estimation between 2017 and 2022 for the KG basin region. It is inferred from the study that the region has shown surface subsidence of 80 mm/year between April 2020 and June 2022. This study uses support vector regressor (SVR) to predict the loss in forest cover in terms of RVI using MTInSAR-based surface subsidence, VH, and VV backscatter as parameters. It is observed that the SVR gave R2-statistics of 0.89 and 0.873 in the training and testing phases with a mean absolute error (MAE) and root mean squared error (RMSE) of 0.08 and 0.02, respectively. It is also observed that the region showed a loss of 3.21 km2 of cultivable land between 2020 and 2022.

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.

Control of surface deformation and overburden movement in coal mine area by an innovative roadway cemented paste backfilling method using mining waste.

Caving mining method could lead to massive waste rocks hauled to surface while leaving a large void in underground. This would eventually result in the surface subsidence and damage to the environment and surface infrastructures. In this study, we proposed three different backfilling methodologies to minimise the surface subsidence being 1) 100 % mining and 100 % backfilling (method 1); 2) leaving one slice of coal between two backfilled slices (method 2) and 3) leaving one slice of coal between one backfilled slice (method 3). The backfilling materials are made of waste rock, fly ash and cement and the optimal ratio has been found through the test program designed based on the orthogonal experiment design method. The strength of the backfilling paste is 3.22 MPa at the axial strain 0.033. The mine scale numerical simulation has also been conducted and it was concluded that the method 1 would lead to 0.098 m roof deformation in underground roadway whereas the method 2 and method 3 only induced a roof deformation around 32.7 % and 17.3 % of that induced by the method 1, respectively. All three methodologies have been approved to minimise the roof deformation and disturbance to the rock by mining operations. At last, the surface subsidence has been scientifically evaluated based on the probability integration method of surface movement. It indicated that the surface subsidence, horizontal movement, inclined movement and curvature of rock surrounding the panel void were all below the minimum value required by regulation. This confirmed that the selected backfilling mining is able to ensure the integrity of the surface infrastructures. This technology provides a new way to control the surface subsidence caused by coal mining.

Developmental Features, Influencing Factors, and Formation Mechanism of Underground Mining-Induced Ground Fissure Disasters in China: A Review.

Mining-induced ground fissures are one of the major geological disasters affecting coal mines. In recent years, many effective monitoring methods have been developed to explore the developmental characteristics and nature of mining-induced ground fissures for being treated scientifically. This paper is mainly on the development law and mechanism of mining ground fissure research results which have been comprehensively combed, highlighting the development trend, including the formation condition, development features, influencing factors, and mechanical mechanism of mining-induced ground fissures. Outstanding issues are discussed and future research hot spots and trends are pointed out. The major conclusions include: (1) under the shallow coal mining condition, because the rock layer fault zone directly reaches the surface, the ground fissure usually develops seriously; (2) mining-induced ground fissures are generally divided into four types: tensile fissures, compression fissures, collapsed fissures, and sliding fissures; (3) mining-induced ground fissures are affected by the coupling effect of underground mining and surface topography. The main factors are geological mining conditions, surface deformation, and surface topography, including rock and soil structure, rock and soil mechanical properties, surface horizontal deformation, surface slope, and so on; and (4) to ensure the safety of underground mining, temporary ground fissures formed during the process of coal mining must be treated when ground fissures and rock ground fissures are connected. The results of this article make up for the deficiencies of the relevant research, provide the basis and direction for future research, and have universal applicability and scientific guiding significance.

Influence of Coal Mining on Historical Buildings: Case Study in Shanxi.

Numerous historical buildings exist in Shanxi Province, a major coal producing area in China, so there exist many overlapping areas between ancient wooden buildings and coal mining. Coal mining in overlapping areas will lead to surface subsidence, which will have an impact on historical buildings. Based on the distribution of historical buildings and the distribution and mining of coal resources in Shanxi Province, this paper concludes that the overlapping areas of coal mining and ancient wooden buildings in Shanxi Province are mainly concentrated in Changzhi City, and the Lu'an mining area in Changzhi City is selected as the research object. In addition, using the gray correlation analysis method, the surface subsidence coefficient, which characterizes the intensity of mining subsidence, is used as the reference sequence. Seven factors selected from the geological conditions and mining conditions of the Lu'an mining area are used as the comparison sequence to calculate the gray correlation between each influencing factor and the surface subsidence coefficient, and to obtain that geological factors such as the nature of the overlying rock layer, bedrock thickness and dip angle of the coal seam, and mining factors such as mining height, average mining depth and working face size largely determine the surface subsidence coefficient. The surface subsidence in the overlap area could largely be influenced by geological factors such as the nature of the overlying rock layer, bedrock thickness and coal seam inclination, and mining factors such as mining height, average mining depth and working face size. Finally, we investigate the possible effects of surface subsidence on ancient wooden buildings in the overlapping area with the surface subsidence and formation mechanism and propose technical measures to reduce the effects of surface subsidence due to coal mining on historical buildings in the overlapping area.

Study on Regional Strata Movement during Deep Mining of Erdos Coal Field and Its Control.

Disasters such as rock bursts and mine earthquakes became increasingly serious with the increase in mining depth in Erdos Coal Field and became serious problems that restrict high-strength continuous mining of coal mines. In this study, strata movement and energy polling distribution of ultrathick weak-bonding sandstone layers were controlled by the local filling−caving multi-faces coordinated mining technique, which was based on the analysis of subsidence and overlying structural characteristics in the Yingpanhao mining area. Moreover, the influencing factors and the control effect laws were investigated. Surface subsidence and energy polling distribution control effects of different mining modes were compared, which confirmed the superiority of local filling based on the main key stratum. According to the results, the maximum surface subsidence velocity of the first mining face was 1.24 mm/d, which indicates the presence of a logistic functional relationship between the mining degree and subsidence factors. When the mining degree was close to full mining, the practical surface subsidence was smaller than the corresponding logistic functional value. The largest influencing factor for the strata movement control effect of partial filling mining based on the main key stratum was the width of the caving face, followed by the filling ratio, section pillar width, and width of the filling face, successively. With respect to the influencing degree on the energy polling distribution of partial filling mining based on the main key stratum, the order followed as section pillar width > filling ratio > caving working face > width of backfilling working face. Additionally, the comparative analysis from the perspectives of control effect, resource utilization, and cost-effectiveness demonstrated that partial filling mining based on the main key stratum was one of the techniques with high cost-effectiveness in controlling strata movement and relieving rock bursts, mining earthquakes, and subsidence disasters.

Monitoring and Analysis of Ground Surface Settlement in Mining Clusters by SBAS-InSAR Technology.

In this paper, we use the small baseline set technology and the early geological hazard identification method based on the selection of Permanent Scatter (PS) and Distributed Scatter (DS) points to carry out the research on surface deformation monitoring caused by underground activities in mining cluster areas. We adopted the Small Baseline Subset InSAR (SBAS-InSAR) technique to process Sentinel-1A SAR images over the research area from March 2017 to May 2021. The deformation estimation technology based on the robustness of PS points and DS points can be used for early identification of high-density surface subsidence in a large area of mines. The surface subsidence information can be obtained quickly and accurately, and the advantages of using InSAR technology to monitor long-time surface subsidence in complex mining cluster areas was explored in this study. By comparing the monitoring data of the Global Navigation Satellite System (GNSS) ground monitoring equipment, the accuracy error of large-scale surface settlement information is controlled within 8 mm, which has high accuracy. Meanwhile, according to the spatial characteristics of cluster mining areas, it is analyzed that the relationship between adjacent mining areas through groundwater easily leads to regional associated large-area settlement changes. Compared with the D-InSAR (Differential InSAR) technology applied in mine monitoring at the early stage, this proposed method can monitor a large range of long time series and optimize the problem of decoherence to some extent in mining cluster areas. It has important reference significance for early monitoring and early warning of subsidence disaster evolution in mining intensive areas.

Freeze-thaw vacuum treatment of landfill sludge: Mechanism of uneven frost heaving and dewatering performance.

The method of freeze-thaw combined with vacuum pretreatment for landfill sludge (LS) has attracted extensive attention. However, most of the existing approaches are based on small-scale laboratory testing, and further testing studies must be performed to realize in situ treatment. To enhance the practicality of such approaches, the range of temperature effects on LS was analysed after field freeze-thaw model testing. After the freeze-thaw model test, samples were transported to the laboratory for unidirectional oedometer tests, and the remaining samples were retained in the field to continue vacuum model testing for exploring the differences in the consolidation and drainage effect of the LS. Results show that temperature changes during freeze-thaw process affect the distribution of sludge and water in the model boxes, resulting in frost heave and the appearance of "extrusion rings". In addition, the coefficient of consolidation obtained from the unidirectional oedometer test shows that the consolidation coefficient is generally larger near the freezing tubes at a lower temperature. The settlement determined from the field vacuum preloading test shows that the subsequent vacuum consolidation settlement is larger at the position with a lower elevation of the frozen sludge surface. The comparison indicates that the consolidation and drainage effect in the field is not as significant as that in the laboratory. The findings can provide reference to optimize the field conditions during the in situ engineering practice of sludge treatment.

Mining footprint of the underground longwall caving extraction method: A case study of a typical industrial coal area in China.

Longwall caving mining (LCM) can lead to many environmental problems that have drawn worldwide attention. A previous survey found that most scholars tend to analyze the two issues separately, that is, coal mining-induced subsidence and heavy metal pollution sources in the soil of the mining regions. Based on field monitoring as well as the collection and analysis of soil samples, a previous study estimated ground settlement and analyzed the surface subsidence law and spatial distribution characteristics of heavy metals in soils. Moreover, a geographic information system was combined with multivariate statistical analysis methods to analyze the heavy metal pollution sources in soils. At the same time, the mechanism of heavy metal accumulation in the subsidence area was analyzed. The study found that the most active subsidence of settlement was 137.5 m behind the workface and moved forward with the workface. LCM has already caused significant disturbance to the soils in the Hengyuan Mine. Moreover, the distribution pattern of eight heavy metals was consistent with the surface subsidence law. The sources of heavy metal pollution in the soils were also identified; namely, coal mining-induced subsidence (64.1%) and mixed transportation and wind-mediated spread (35.9%), offering a reinterpretation of the LCM's footprint.

Comparison of Surface Subsidence Measured by Airborne and Satellite InSAR Over Permafrost Areas Near Yellowknife Canada.

In addition to spaceborne Interferometric Synthetic Aperture Radar (InSAR), airborne data such as those obtained by the Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) have also been utilized to measure surface subsidence in permafrost areas in recent years. Motivated by the integration of multiplatform InSAR data, we generated two UAVSAR interferograms and one Advanced Land Observing Satellite (ALOS)-2 L-band interferogram over a permafrost area near Yellowknife, Canada, then compared the surface subsidence in the thaw seasons of 2017. The correlation coefficient and the root mean square error (RMSE) of subsidence difference are calculated to compare the airborne and spaceborne InSAR measurements. The results demonstrate that the two UAVSAR measurements are self-consistent, with the correlation coefficient between independent airborne measurements ∼0.7. While the RMSE of the difference between surface subsidence measured by UAVSAR and ALOS2 is ∼2.0 cm, and the correlation coefficients are less than 0.41, that is, a noticeable deviation exists between the UAVSAR and ALOS2 results possibly due to different spatial resolution and the calibration processing of airborne and spaceborne InSAR data. In addition, both UAVSAR and ALOS2 interferograms show larger surface subsidence within taiga needleleaf forest regions than in regions of other biome types (including needleleaf forest, shrubland, and grassland). The results demonstrate that a scheme for the elimination of systematic differences needs to be developed before merging multisource InSAR results. This intercomparison will provide valuable insights for narrowing the gap between radar-based measurements and planning the integration of airborne and satellite InSAR measurements in permafrost environments.

Assessment of cemented waste rock backfill for recycling gangue and controlling strata: creep experiments and models.

Filling mining with cemented waste rock backfill (CWRB) is an optimal approach to eliminate the gangue waste pollution. To efficiently evaluate the gangue recycling and its advantage in structure protection, the effects of the confining pressure, cement dosage, and aggregate particle size distribution (PSD) on the creep behavior of CWRB were investigated. Burgers creep model was used to characterize the visco-elastic characteristics of CWRB, a visco-elastic-plastic creep model was established to describe its creep behavior on this basis. A genetic algorithm (GA) for optimizing the model parameters was constructed to verify the creep model. The time-varying evolutions of strata movements were discussed to evaluate the effect of the creep behavior of CWRB on the structural safeties. The results show that the creep load levels and times are positively correlated with the confining pressure and cement dosage, indicating that the consideration of roof load without confining pressure of surrounding rock causes an increase in the design parameters of CWRB to waste the cementing material. The creep load levels and times firstly increase and then decrease with the Talbot gradation index, revealing that CWRB with superior aggregate PSD performs the strong anti-deformation capacity under creep condition. The confining pressure, cement dosage, and aggregate PSD are comprehensively considered to optimize CWRB, and its stability under creep condition causes the strata movement to gradually slow down, thereby protecting underground aquifers and surface buildings.

Environmental behavior of construction and demolition waste as recycled aggregates for backfilling in mines: Leaching toxicity and surface subsidence studies.

Environmental behavior of construction and demolition waste in cemented backfilling mining technology (CW-CBMT) is studied, with the aim of expanding the scope of construction and demolition waste (CDW) utilization, as well as developing strategies to release coal resources. Toxicity leaching, scanning electron microscopy (SEM), and mechanical properties testing about on-site sampling are carried out, and surface subsidence is surveyed. The results reveal that the maximum leaching concentration (0.00113 mg/L) of arsenic from cemented backfilling body with construction and demolition waste (CBCW) is small, the leaching solution is alkaline, and the leaching of heavy metals is influenced by aggregate particle size and by acidity and alkalinity. The results also show that the average compressive strength of CBCW is 2.4 MPa. The distribution of aggregates and elemental content influence the spatial distribution of compressive strength. The variation of internal distribution of elemental content of the CBCW can be interpreted by multifractal parameters. The maximum surface subsidence value is 245 mm, with the fastest sinking speed occurring in the mining stage and a return of surface subsidence stability after halting of mining. A comprehensive analysis of the test results shows that, from an environmental viewpoint, the application of CW-CBMT is successful.

Surface Subsidence Analysis by Multi-Temporal InSAR and GRACE: A Case Study in Beijing.

The aim of this study was to investigate the relationship between surface subsidence and groundwater changes. To investigate this relationship, we first analyzed surface subsidence. This paper presents the results of a case study of surface subsidence in Beijing from 1 August 2007 to 29 September 2010. The Multi-temporal Interferometric Synthetic Aperture Radar (multi-temporal InSAR) technique, which can simultaneously detect point-like stable reflectors (PSs) and distributed scatterers (DSs), was used to retrieve the subsidence magnitude and distribution in Beijing using 18 ENVISAT ASAR images. The multi-temporal InSAR-derived subsidence was verified by leveling at an accuracy better than 5 mm/year. Based on the verified multi-temporal InSAR results, a prominent uneven subsidence was identified in Beijing. Specifically, most of the subsidence velocities in the downtown area were within 10 mm/year, and the largest subsidence was detected in Tongzhou, with velocities exceeding 140 mm/year. Furthermore, Gravity Recovery and Climate Experiment (GRACE) data were used to derive the groundwater change series and trend. By comparison with the multi-temporal InSAR-derived subsidence results, the long-term decreasing trend between groundwater changes and surface subsidence showed a relatively high consistency, and a significant impact of groundwater changes on the surface subsidence was identified. Additionally, the spatial distribution of the subsidence funnel was partially consistent with that of groundwater depression, i.e., the former possessed a wider range than the latter. Finally, the relationship between surface subsidence and groundwater changes was determined.