Search Results (17)

Roof water inrush is a major hazard threatening coal mine safety. This paper addresses the risk of roof water inrush during mining in the shallow-buried Jurassic coalfield of Northern Shaanxi, taking the Guojiawan Coal Mine as a case study. A systematic framework of “identification of main controlling factors–coupling of subjective and objective weighting–GIS-based spatial evaluation” is proposed. An integrated weighting system combining the Fuzzy Analytic Hierarchy Process (FAHP) and the Coefficient of Variation (CV) method is innovatively adopted. Four weight optimization models, including Linear Weighted Method, Multiplicative Synthesis Normalization Method, Minimum Information Entropy Method, and Game Theory Method, are introduced to evaluate 10 main controlling factors, including the fault strength index and sand–mud ratio. The results indicate that the GIS-based vulnerability evaluation model using the Multiplicative Synthesis Normalization Method achieves the highest accuracy, with a Spearman correlation coefficient of 0.9961. This model effectively enables five-level risk zoning and accurately identifies high-risk areas. The evaluation system and zoning results developed in this paper can provide a direct scientific basis for the design of water prevention engineering and precise countermeasures in the Guojiawan Coal Mine and other mining areas with similar geological conditions. Full article

In the semi-desert aeolian sand areas of Northern China, surface deformation monitoring with SAR is challenged by loss of coherence due to mobile dunes, seasonal vegetation changes, and large-gradient, nonlinear subsidence from underground mining. This study utilizes PALSAR-2 (L-band, 3 m resolution) and Sentinel-1 (C-band, 30 m resolution) data, applying InSAR and Offset tracking methods combined with differential, Stacking, and SBAS techniques to analyze deformation monitoring effectiveness and propose an efficient dynamic monitoring strategy for the Shendong Coalfield. The main conclusions can be summarized as follows: (1) PALSAR-2 data, which has advantages in wavelength and resolution (L-band, multi-look spatial resolution of 3 m), exhibits better interference effects and deformation details compared to Sentinel-1 data (C-band, multi-look spatial resolution of 30 m). The highly sensitive differential-InSAR (D-InSAR) can promptly detect new deformations, while Stacking-InSAR can accurately delineate the range of rock strata movement. SBAS-InSAR can reflect the dynamic growth process of the deformation range as a whole, and SBAS-Offset is suitable for observing the absolute values and morphology of the surface moving basin. The combined application of Stacking-InSAR and Stacking-Offset methods can accurately acquire the three-dimensional deformation field of mining-induced strata movement. (2) The spatiotemporal process of surface deformation caused by coal mining-induced strata movement revealed by InSAR exhibits good correspondence with both the underground mining progress and the development of ground fissures identified in UAV images. (3) The maximum displacement along the line of sight (LOS) measured in the mining area is approximately 2 to 3 m, which is close to the 2.14 m observed on site and aligns with previous studies. The calculated advance influence angle of the No. 22308 working face in the study area is about 38.3°. The influence angle on the solid coal side is 49°, while that on the goaf side approaches 90°. These findings further deepen the understanding of rock movement and surface displacement parameters in this region. The dynamic monitoring strategy proposed in this study is cost-effective and operational, enhancing the observational effectiveness of InSAR technology for surface deformation due to coal mining in this area, and it enriches the understanding of surface strata movement patterns and parameters in this region. Full article

In recent years, controlling the integrity of shallow-buried natural gas pipelines within surface subsidence zones caused by high-intensity underground longwall mining in the Daniudi Gas Field of China’s Ordos Basin has emerged as a critical challenge impacting both mine planning and the safe, efficient co-exploitation of coal and deep natural gas resources. This study included field measurements and an analysis of surface subsidence data from high-intensity longwall mining operations at the Xiaobaodang No. 2 Coal Mine, revealing characteristic ground movement patterns under intensive extraction conditions. The subsidence basin was systematically divided into pipeline hazard zones using three key deformation indicators: horizontal strain, tilt, and curvature. Through ABAQUS-based 3D numerical modeling of coupled pipeline–coal seam mining systems, this research elucidated the spatiotemporal evolution of pipeline Von Mises stress under varying mining parameters, including working face advance rates, mining thicknesses, and pipeline orientation angles relative to the advance direction. The simulations further uncovered non-synchronous deformation behavior between the pipeline and its surrounding sand and soil, identifying two distinct evolutionary phases and three characteristic response patterns. Based on these findings, targeted pipeline integrity preservation measures were developed, with numerical validation demonstrating that maintaining advance rates below 10 m/d, restricting mining heights to under 2.5 m within the 260 m pre-mining influence zone, and where geotechnically feasible, the maximum stress of the pipeline laid perpendicular to the propulsion direction (90°) can be controlled below 480 MPa, and the separation amount between the pipe and the sand and soil can be controlled below 8.69 mm, which can effectively reduce the interference caused by mining. These results provide significant engineering guidance for optimizing longwall mining parameters while ensuring the structural integrity of shallow-buried pipelines in high-intensity extraction environments. Full article

This study investigates the impact of weak water-rich aquifers overlying shallow-buried thin bedrock coal seams on mining support systems. By applying Terzaghi’s theory to the evolutionary characteristics of the overburden structure in loose aquifers, a mechanical model for load transfer from the aquifer is established, and a calculation formula for the maximum working resistance of the support is derived. The results are validated using field mine pressure data from the 1010–1 working face of Wugou Coal Mine. The findings show that the overlying load of the key stratum is positively correlated with the water pressure in the aquifer; the higher the water pressure, the greater the overlying load, which leads to increased instability of the key stratum and a higher likelihood of support crushing. Additionally, the thickness of the bedrock is negatively correlated with the aquifer water pressure load transfer coefficient, meaning that a thicker bedrock layer reduces the impact of the aquifer’s water pressure on the key stratum, with a critical thickness of 50 m. Moreover, the working resistance of the support is positively correlated with the water pressure, and the pressure intensity at the working face in the aquifer-covered area after grouting reconstruction is about 33% higher than in non-aquifer-covered areas. The results provide a theoretical basis for safe mining in similar geological conditions and offer guidance for the selection of support systems. Full article

To learn more about the problem of blast weakening in shallow-buried and extra-thick coal seams, Panjin coal mine was used to provide the engineering background for this study. The influence of blast weakening technology on the vibration of ground buildings was investigated. Based on monitoring the vibration data from the final 400 m of the working face, we established the Sadovsky formula for this coal mine through regression. The maximum safe charge of one blast at different distances was obtained. A numerical model was established and compared with field monitoring data to verify its accuracy. This numerical model was used to analyze the influence of blast weakening vibrations on ground buildings during the final mining stage. Finally, the maximum safe charge for one blast at advancing distances from the working face was derived based on numerical calculation results. It was compared with the maximum safe charge obtained from field measurements. The results show that both exhibit significant consistency, and the maximum safe charge of one blast decreases as the working face advances. In addition, the peak vibration velocity at each monitoring point does not exceed 0.2 cm/s for the remaining 400 m of the measured working face, which is lower than the allowable safety value for blasting vibrations. In the numerical simulation of the final mining stage at 200 m, the ground vibration velocity is largest for the district office, second-largest for the chimney, and smallest for the science and technology building. The maximum vibration velocity and effective stress in the three directions of the three buildings are within the allowable range, indicating that the buildings remained in a safe state. Full article

To address the feasibility of gob-side entry retaining in the shallow-buried three-soft coal seam fully mechanized mining face (SB-TSCS FMMF) of Xindeng (Zhengzhou, China) Coal Industry, we established a mechanical model of post-mining roof–coal-rock interaction in shallow-buried three-soft coal seams. This study reveals the quantitative relationships between the fracture position of the main roof and parameters such as coal seam thickness and immediate roof elastic modulus, and determines the parameter conditions required for implementing gob-side entry retaining in SB-TSCS FMMF. Critical parameters for the main roof fracture under this geological condition were first identified through particle flow simulation. The results indicate that there exist quantitative relationships between the main roof fracture position and parameters of the coal seam and the immediate roof. The influence degree on the maximum force exerted by the main roof on underlying coal-rock strata decreases in descending order as follows: immediate roof elastic modulus, coal seam thickness, immediate roof thickness, and coal seam elastic modulus. Similarly, the influence degree on the maximum bending moment follows the same order: immediate roof elastic modulus, coal seam thickness, immediate roof thickness, and coal seam elastic modulus. Based on the roof fracture laws, parameter thresholds suitable for gob-side entry retaining in three-soft coal seams are proposed, such as coal seam thickness (≤4 m) and immediate roof thickness (≤8 m). It is found that the main roof fracture position in shallow-buried three-soft coal seams is concentrated within the 0.3–0.6 m stress-sensitive zone at the edge of the goaf, providing key parameter thresholds for the support design of gob-side entry retaining. Full article

In China’s northwest mining areas, shallow buried coal seams commonly feature double soft composite roof structures of mudstone and clay, resulting in poor roadway stabilization and proving challenging for effective roadway-surrounding rock (RSR) control. A mudstone–clay composite roof is particularly difficult to maintain due to the complex interactions between the soft rock layers and their sensitivity to moisture changes. Previous studies have investigated the properties of these soft rocks individually, but there is limited research on the behavior and control of double soft composite roofs. This study investigated the hydrophilic mineral composition and microstructure of mudstone and clay through X-ray diffraction (XRD) and scanning electron microscopy (SEM) experiments. Through an orthogonal experimental design, the influence of the clay layer thickness, number of layers, layer position, and relative moisture content on the stability of a mudstone–clay composite roof was studied. The results revealed the following: (1) Kaolinite, the primary hydrophilic component, constitutes a high proportion of clay, while both mudstone and clay exhibit abundant pores and cracks under SEM observation; (2) The relative moisture content emerged as the most significant factor affecting roadway deformation; and (3) A combined support of bolts, a short anchor cable, and a long anchor cable effectively controls RSR deformation in the case of a double soft composite roof. The methodology combining comprehensive material characterization and systematic parametric analysis can be extended to the study of other complex soft rock engineering problems, particularly those involving moisture-sensitive composite roof structures. Full article

Accurate prediction of the height of water-conducting fissure zone (HWCFZ) is an important issue in coal water control and a prerequisite for ensuring the safe production of coal mines. At present, the prediction model of HWCFZ has some issues such as poor prediction accuracy. Based on the widely collected measured data of the HWCFZ in different coal mines in northern Shaanxi Province, China, the HWCFZ in shallow-buried coal seams is categorized into two types, i.e., typical shallow-buried coal seams and near-shallow-buried seams, according to the different depths of burial and base-loading ratios. On the basis of summarizing the research results of the previous researchers, three factors, namely, mining thickness, coal seam depth, and working length, were selected, and the data of the height of the water-conducting fissure zone in the study area were analyzed by using a multivariate nonlinear regression method. Subsequently, each group of the data was randomly divided into training data and validation data with a ratio of 70:30. Then, the training data were used to build a neural network model (BP), random forest model (RF), a hybrid integration of particle swarm optimization and the support vector machine model (PSO-SVR), and a hybrid integration of genetic algorithm optimization and the support vector machine model (GA-SVR). Finally, the test samples were used to test the model accuracy and evaluate the generalization ability. Accordingly, the optimal prediction model for the typical shallow-buried area and near-shallow-buried area of Jurassic coal seams in northern Shaanxi was established. The results show that the HWCFZ for the typical shallow-buried coal seam is suitable to be determined by the multivariate nonlinear regression method, with an accuracy of 0.64; the HWCFZ for near-shallow-buried coal seams is suitable to be predicted by the two-factor PSO-SVR computational model of mining thickness and the burial depth, with a prediction accuracy of 0.84; and machine learning methods are more suitable for near-shallow-buried areas, dealing with small-scale data and discrete data. Full article

In the context of a shallow-buried thin coal seam, the surrounding rock deformation in the semi-coal rock roadway is comparatively small, resulting in self-stabilization of the two sides of the roadway without the need for support when the roadway is below a critical width. This study focuses on the transportation roadway of the 2107 working face in the Anzhe Coal Mine, employing a combination of laboratory tests, field tests, theoretical analyses, and numerical simulations. A mechanical model for the layered roof of the semi-coal rock roadway in a shallow-buried thin coal seam is developed, along with a calculation formula for determining the critical width of such roadways. The study also initially examines the correlation between the critical width and factors such as the tensile strength of the roof, the buried depth of the roadway, and the thickness of the immediate roof strata under conditions where the coal sides of the roadway are self-stabilizing. The results showed the following. (1) The calculation formula has good applicability for typical shallow-buried mine roadways in the Niuwu mining area and shallow-buried semi-coal rock roadways with coal thickness below 0.7 m under similar geological conditions. The critical width is related to the tensile strength of the roof, the buried depth of the roadway, and the thickness of the immediate roof strata. The degree of influence is determined by the thickness of the immediate roof strata > the tensile strength of the roof > the buried depth of the roadway. Among these, the tensile strength of the roof, the thickness of the immediate roof strata, and the critical width are basically in a positive exponentially increasing relationship, and the buried depth of the roadway and the critical width are basically in a negative exponentially decreasing relationship. (2) The on-site measurement of the loose circle on both sides of the roadway revealed that the rock mass loose circle had a thickness of 0.2 m, while the coal loose circle had a thickness ranging from 0.6 m to 0.7 m, aligning closely with the results obtained from theoretical calculations. The thickness of the coal loose circle on both sides served as the basis for determining the critical width of the semi-coal rock roadway in the shallow-buried thin coal seam. The calculated critical width of the roadway was 2.9 m, whereas the actual width measured was 2.4 m. Consequently, the two sides of the roadway are deemed capable of self-stabilization in the unsupported state. (3) Following the optimization of the support scheme, engineering analysis indicates that the roof and floor exhibit a maximum convergence of 46.3 mm, while the two sides show a maximum convergence of 18.4 mm. It is observed that the surrounding rock of the roadway satisfies the safety requirements for production. This study can provide theoretical support and a scientific basis for the stability discrimination of two sides and surrounding rock control of semi-coal rock roadways in shallow-buried thin coal seams under similar conditions. Full article

Shallow-buried, hard, and extra-thick coal seams are very common in Xinjiang, China, but there are relatively few studies on the mine pressure law and the development characteristics of water-flowing fracture zones (WFFZs) during the mining of such coal seams. In this paper, the mine pressure of the top coal caving face in a shallow, hard coal seam with a hard roof and full bedrock (SHCSHRFB) is analysed, the laws of the surrounding rock deformation and stress of the open-off cut and roadway in the large-mining-height top coal caving face are studied, the characteristics of roof-breaking and overburden fracture development are analysed using the physical similarity simulation method, supporting suggestions for roadways are put forward, and three development stages of the WFFZ are analysed. Field monitoring shows that the hydraulic support stress in SHCSHRFB is weak, but the coal wall and roadway stability are good, which is significantly different from the results in the typical shallow-buried thin bedrock working faces. The measured height of the WFFZ is close to the physical similarity simulation results, but quite different from those arising from use of the empirical formula. Full article

Coal is one of the important energy sources for industry. When it is mined, it will cause the destruction of bedrock and surface. However, it is more severe in mining shallow-buried multi coal seams (SBMCS). To better reveal the characteristics of the bedrock and surface damage, we have carried out a theoretical analysis, as well as used numerical simulations and field monitoring methods to study the surface and bedrock damage caused by the mining of SBMCS. The characteristics of bedrock and surface failure structure, settlement, and stress distribution were studied and analyzed. The findings show that the collapsed block, formed by the rupture of the overlying stratum, interacts with the surrounding rock to form large cavities and gaps, and the stress concentration occurs between them. The maximum downward vertical concentration stress is about 9.79 MPa. The mining of the lower coal seam can lead to repeated failure of the upper bedrock and goaf. The settlement of bedrock presents gradient change, and the settlement of upper bedrock is large, about 8.0 m, and the maximum settlement is 8.183 m, while that of lower bedrock is small and about 3.5–4.0 m. The weak rock stratum in the bedrock is crushed by the change stress of repeated mining, and formed a broken rock stratum. The cracks in the bedrock develop directly to the ground. On the ground, tensile cracks, compression uplift, stepped cracks, and even collapse pits are easy to cause in mining SBMCS. Affected by repeated mining, the variation of surface vertical stress is complex and disorderly in the middle of the basin, and the variation of horizontal stress is mainly concentrated on the edge of the basin. The maximum stress reaches 100 KPa, and the minimum stress is about 78 KPa. Through theoretical analysis and discussion, the size of the key blocks is directly related to the thickness and strength of the rock stratum. Full article

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. Full article

An observatory was established at the Ningtiaota Mine (China) in order to investigate the surface deformation pattern of N00 method workings mining in shallow buried thick coal seams in a windy-sand area. The observatory allows one to measure the coupling between the periodic changes of parameters related to ground subsidence and ground cracks with workings advancement. The data monitored in the field indicate that when the adjacent mining workings are mined below the ground, a sinkhole basin with a larger impact area will be formed. New ground fractures are formed above the mining area to connect with the fractures above the mining face. As a consequence a new pattern of “O” circle distribution beyond the working face is formed, which develops rapidly during the working face recovery. In addition, the dynamic fractures in coal mining are characterized by the phenomenon of self-healing. Our findings will help to protect the surface environment of the mine area during shallow buried high-intensity mining activities in the Lime Tower coal mine, and are also an important guideline in other windy beach mining areas. Full article

In the mining stage of shallow thick coal seam in the western mining area of China, there is often severe mine pressure and serious surface subsidence and damage. In this paper, theoretical analysis and PFC (Particle Flow Code) numerical simulation are combined to study the caving characteristics and force chain evolution characteristics of the overlying strata of stope. We analyze the stability of the structure of the “inclined step cutting body” on the overlying strata and obtain the calculation formula of the support force of the working face based on the instability of the structure. The force chain arch curve equation is modified according to the evolution law of force chains, from which the force chain can be the basis for judging the large area damage of the surface. The results demonstrate that the rock mass i₁ ≤ 0.86, the structure of “inclined step cutting body,” is not prone to sliding and instability. Considering that i = 1.0~1.4 under the condition of shallow buried thick coal seam, the structure of the “inclined step cutting body” is prone to being destroyed leading to instability, resulting in severe rock pressure.The minimum supporting force to maintain structural stability is 0.2F_n, which is in line with the actual support force in the mining process of the working face. Taking the mining technical parameters of the nearby working face into the force chain arch formula, it can be concluded that, when the working face advances to 175 m, large-scale subsidence damage begins to appear on the surface, which agrees with the survey results. Therefore, the force chain is the main force system to bear the load of the overlying strata. PFC has unique advantages in simulating discontinuous deformation of overburden rock. The results of the study reasonably explain the phenomena of severe mine pressure and serious surface damage caused by the mining of the shallow thick coal seam working face, which has a certain reference value for preventing ground disasters caused by underground mining and land ecological restoration. Full article

The weakening of hard coal–rock mass is the core common problem that is involved in the top coal weakening in hard and thick coal seams, the hard roof control during the initial mining stage in the longwall mining face, and the hanging roof control in the gob of non-coal mine. Based on the characteristics of pulse hydraulic fracturing and constant pumping rate hydraulic fracturing, a weakening method for hard coal–rock mass by combining pre-pulse and constant pumping rate hydraulic fracturing is proposed. A complete set of equipment for the combined pulse and constant pumping rate hydraulic fracturing construction in the underground coal mine is developed. The pulse and constant pumping rate hydraulic fracturing technology and equipment were applied in the top coal weakening of the shallow buried thick coal seam. Compared with no weakening measures for top coal, the average block size of the top coal caving was reduced by 42% after top coal hydraulic fracturing. The recovery rate of the top coal caving mining face reached 85%, and it increased by 18% after hydraulic fracturing. Full article