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The advanced deep hole blasting (ADHB) is commonly used to improve the fragmentation of thick hard top coal in longwall top coal caving (LTCC) mining. This paper presents an acoustic method to quantitatively evaluate the effectiveness of the ADHB. First, the variations of P‐wave velocity of hard coal samples under uniaxial and triaxial compression are obtained from the laboratory acoustic test. Then, an acoustic wave method based on seismic tomography is proposed to assess the effectiveness of the ADHB by introducing the P‐wave velocity attenuation model into the data processing. Finally, a field seismic tomography test is conducted to obtain the distribution of the P‐wave velocity of top coal before and after the ADHB implementation. And the P‐wave velocity attenuation is calculated to estimate the fragmentation effectiveness of ADHB. The results indicate that the P‐wave velocity attenuation model could well represent the broken degree of hard coal, suggesting that the proposed acoustic wave method could quantitatively evaluate the fragmentation effectiveness by exporting the nephogram of P‐wave velocity attenuation. The present study may provide technical support for improving the recovery ratio of thick hard top coal for LTCC mining.

The purpose of this study is to achieve better understanding of associated mechanisms and to recommend and identify new strategies to develop new rock breaking technology for Tunnel Boring Machines (TBMs). Tunnel Boring Machine tunnelling mainly depends upon the rock breakage caused by cutters moving on a rock surface in a rolling and sliding motion while under the action of thrust force. The rock breaking behaviour is controlled by the mechanical interaction between the cutters and the rock. Due to the high hardness and high abrasiveness of rock, the cutters have to work under very high thrust force and suffer heavy‐load‐impact and abrasive wear, causing serious wear and low rock breaking efficiency. Rock‐boring organisms exist in nature, which achieve drilling and/or tunnelling in rocks through a tribochemical interaction. This phenomenon is called bioerosion and the organisms are natural ‘TBMs’ to some degree. In this study, the interaction between TBM cutters and rock is presented, and current measures to improve cutter wear and rock breaking efficiency and their limitations are reported. Then, the connotation, mechanism and typical cases of bioerosion are presented. Finally, inspired by bioerosion, a new chemically assisted rock breaking technology is proposed for TBMs.

The migrant families who build India’s cities do so to meet practical and ritual aspirations rooted in the village, undergoing spatial and temporal fragmentation to maintain rural longevity and the possibilities of ritual time. This article contributes an alternative position to linear-framed presumptions of migration and urbanity, illustrating instead how everyday experiences of dislocation can be productive through labor, timespace, and imagination; bridging the gulf between residence on urban construction sites in Bengaluru, southern India, and desired village homes. However, lived experiences of dislocation remain stratified by gender and class, leading to highly conjugated experiences of precarity, mobility, and possibility. Despite the urban ambivalence felt by women and girls as a result, a shared experience of dislocation enables entire families to undertake the grueling yet regenerative work of circular migration, ensuring the continuation and renewal of village life and ritual time through its incompleteness.

The current in situ stress regime is of great significance to the exploration and development of coalbed methane (CBM). In this study, the vertical stress (σV), maximum horizontal principal stress (σH), and minimum horizontal principal stress (σh) in the Liupanshui Coalfield were studied. Variations of the maximum and minimum envelopes and trend lines of the lateral pressure coefficient (λ) with depth were obtained, and the non‐monotonic decrease of permeability with burial depth was determined. On this basis, the effect of in situ stress on the coal reservoir permeability was evaluated. The results show that the average vertical stress gradient of the main coal seam in the Liupanshui Coalfield is 0.024 MPa/m. Generally, there are two stress regimes of σH > σV > σh (44.23%) and σV > σH > σh (46.15%); σH > σh > σV accounts for a smaller proportion (9.62%), and only occurs in relatively shallow coal seams ( σV > σh is dominant; σV > σH > σh is dominant between 600 and 800 m; and between 800 and 980 m, the coal reservoir is affected by both σH > σV > σh and σV > σH > σh, representing a transition zone between the two stress states. With the increase of burial depth, the permeability of the coal reservoir shows a complex non‐monotonic decline, and the variation of the permeability of the coal reservoir differs under the influence of different stress regimes. Further analysis shows that under the background of stress regime transformation, permeability is mainly affected by the stress value, horizontal principal stress difference, stress regime, and coal cleat, indicating that in situ stress is the main controlling factor of coal reservoir permeability in the Liupanshui Coalfield.

Studies regarding the reuse of a gob‐side roadway formed by the N00 longwall mining method are scarce. To investigate the mine pressure behavior characteristics during roadway reuse, the anchor cable force, roof‐to‐floor deformation, and working resistance of the hydraulic support obtained from the verification working face were analyzed. Test results show that the influence range of the mining‐induced pressure was 0‐90 m in front of the working face. The ratios of the first and periodic weighting steps between the entry‐retaining and non‐roof‐cutting sides were 20.25 and 1.94, respectively. However, the ratios of the ground pressure strengths at the two sides were 1.07 and 1.31, respectively. The results indicate that the monitored roadway can be classified into three deformation zones based on the severity of the mine pressure behavior: large, intermediate, and creep. The main roof between the adjacent working faces exhibited a failure type comprising the “O‐X” and “O‐Y” states, which resulted in an unconventional mine pressure behavior. This study provides insights into the N00 longwall mining method as well as important guidance for tackling similar geological conditions when using this mining method.

Petroleum seeping at the Earth's surface thickens by evaporation of volatiles and bio-degradation to form viscous heavy oil, commonly referred to as tar or pitch, and semi-solid to solid asphalt. Keywords: ancient Near East history; Egyptian history; natural resources

This study combined multi‐field coupled numerical calculations and field measurements to analyze the gas pressure relief and the outburst elimination range of the coal body in the lower side of a gob induced by excavating an inclined seam. A coal seam gas flow solid‐gas coupled model allowing for elastoplastic damage was established based on an inclined longwall panel of the Hongyan Coal Mine in Chongqing, China. To inspect the gas depressurization effect, this study simulated the collapse and damage of strata surrounding the longwall panel after mining by using a constitutive model of the interlayer weak plane, the changes in the damage, gas pressure, and stress concentration in the gob‐side coal seam were analyzed numerically. Besides, variation in gas pressure within 10‐23 m away from the panel margin was measured on‐site during the advancement of the longwall face to validate and modify the results of modeling. The simulation results showed that the advancing of the panel is highly effective in releasing gas from the gob‐side coal body. The rupture penetration, stress concentration, and original elastic zone will be formed in the gob‐side coal body with increasing distance away from the gob after mining the 3603‐2 panel. The permeability increased dramatically and the gas was almost exhausted in the rupture penetration zone. The field measurement results indicated that gas pressure decreased in three stages with advancement. After completion of excavation activities, the drop rates of gas pressure and gas content within 10‐23 m from the gob were 26.55%‐73.58% and 34%‐71%, respectively. Additionally, it was proved that the numerical simulation results were instructive for predicting the range of gas outburst‐proneness elimination belt by comparing simulation and field results, and the outburst elimination range of the inclined longwall panel of the Hongyan Coal Mine was determined to be 10 m.

Coal mining is frequently halted for long periods of time due to geological faults, and the process of resuming mining is often fraught with danger. To address this issue, in this study, the previously developed COMBUSS‐3D software was optimized to simulate the process between mining discontinuation and resumption, based on the multi‐field coupling theory. The optimized software takes the temperature distribution in gobs when coal mining ends as the initial condition, and it considers the condition of spontaneous coal combustion after remining. The actual advance distance of the working face is introduced into the program compilation and solved by linear interpolation. These improvements ensure that the calculation results are more realistic. The results demonstrate that the high‐temperature zone is distributed on the air intake side of the gob, and its final location largely depends on the remining advance rate. The hazardous area of spontaneous ignition gradually moves to a deep suffocation zone of the gob when the mining of the coal wall resumes, the residual coal is no longer oxidized, and CO formation is gradually decreased, which is verified by the theoretical expectations and on‐site observations. The spontaneous combustion period can be effectively prolonged by reducing the thickness of crushed coal during the mining stage or by increasing the longwall advance rate after resuming mining. This study can provide significant guidance and suggestion on locating the hazardous area in gobs and suppressing the spontaneous coal ignition.

The roadway deformation process is closely associated with the accumulation and dissipation of energy. Understanding the characteristics of energy dissipation in surrounding rock is critical to revealing the development process and the disaster mechanisms of the roof accidents in underground coal mines. This paper presents a triaxial compression experiment to analyze energy characteristics of mudstone taken from Huangyanhui Coal Mine. A numerical study is performed to study the energy distribution under different roof strengths. The results suggest that the instability of the roadway is an irreversible energy dissipation process with high nonlinearity and complexity. The roadway support principle, based on the energy balance theory, is proposed to explain the energy distribution. The safety control of roadways with thick and soft roofs should consider the following three aspects: (a) optimize the layout of the roadway, avoid placing it in the stress concentration zone, and reduce the strain energy of the surrounding rock accumulation from the source; (b) improve the ability of the supporting structure to adapt to the deformation of the surrounding rock and avoid the failure of the supporting structure because of excessive force; and (c) set weak structures in the surrounding rock, that dissipate part of the energy, thus reducing the load acting on the support. The results of field application monitoring show that roadway severe deformation was effectively controlled using pressure relief boreholes (PRB), and the average floor heave speed of the roadway decreased from the original 2.0 to 0.98 mm/d. Therefore, PRB provides a new approach for roadway control.

To prevent outbursts and extract the gas, it is necessary to investigate the structure of the key layer and the evolution of cracks during coal mining over a large height. A physical similarity model with a geometric similarity ratio of 1:100 and a strike length of 2 m was established on the basis of prevailing geological and mining conditions. Stress sensors and microseismic equipment were adopted to monitor the collapse characteristics of different key layers through variations in stress and energy. The research results showed that: The displacement of the overlying strata exhibited group motion characteristics marked by the key layer and there was zone of rapidly increasing stress in the goaf behind the working face before and after the fracture of the key layer. Through the analysis of microseismic events, fissure density, and fractal dimension, we found that: before and after the primary key layer fractured, the energy loss in the microseismic event accounted for 27% of the total, the fissure density also changed abruptly from 8 cracks/m to 10 cracks/m and the slope of the fractal dimension curves changed from 0.00243 to 9.94801 × 10−4. Then a gas drainage model suitable for this condition was constructed. When the primary key layer had not fractured, the cracks below fully developed to form a gas migration channel and a gas enrichment area, and gas boreholes could be arranged therein. After the primary key layer had been fractured, the rate of crack development decreased, the permeability would increase, and the gas concentration would increase. The boreholes could still be arranged in the gas migration channel. This study elucidated the control role of the primary key layer from multiple angles and provided experimental guidance for gas drainage over large‐mining heights and during complex key layer mining.

Mylonite coal is a representative of tectonically deformed coal and is a result of crushing original coal into fine coal grains under strong shear or long‐low tectonic stress. Because of its granular nature and the resultant inferior mechanical property, it is difficult to initiate fluid‐driven fractures within mylonitic coal reservoirs for enhancing coalbed methane recovery. The following explores a biomineralization method of microbially mediated calcium carbonate precipitation (MICP) to enhance the structural integrity and mechanical strength of mylonitic coal, enabling potential success for hydrofracturing. The experimental results indicate that the mechanical properties of mylonite coal are significantly enhanced after a short period of MICP treatment with ten cycles of treatments yielding a maximum uniaxial compressive strength (UCS) of 8.7 MPa and a maximum brittleness index of 0.218 approaching that of the hard coal. The increments in UCS and brittleness of biocemented mylonite coal show a positive correlation with the generated calcium carbonate content. Scanning electron microscopy (SEM) imaging indicates that the generated calcium carbonate precipitates first randomly occur on the particle surfaces, and then occupies the interstitial space until particle‐particle bonds are developed. The irregular morphology of coal particles results in two contact relations between particles, point contact and planar contact, causing a significant difference in biocementation effectiveness. Two microfailure patterns of biocemented coal with uniaxial compression are observed. One is that the coal particles are crushed, and the other occurs at the biocemented interface between the coal particles and calcium carbonate crystals.

Examples of the application of microgravity mehtod for the detection of potentially hazardous (empty) underground cavities caused by the collapse of coal mines are presented. Within these areas some alteration by previous remediation activity had occurred. This was not documented earlier and, therefore, such alteration was often unknown prior to the current investigations. We show a successful application of microgravity, leading to the detection of an empty cavity, in close proximity to where concrete injection was earlier performed. This was subsequently verified thorugh measurements in a borehole. In contrast, two other examples delivered results where the microgravity data, along with signals from other geophysical methods, led to the interpretation that subsidence resulting in the formation of sinkholes had been in‐filled, and in these situations the detection of more recent cavities was considered to be unreliable. These results point to the conclusion that microgravity interpretation of cavities is an effective approach, but the success of this approach may be compromised at sites where remediation activity has already occurred; in such situations the approach should be supplemented by other geophysical methods.

With the increase of mining depth, the occurrence mechanism of coal and gas outburst becomes more complex, and stress‐dominated outburst disaster has become one of the major safety problems in deep coal mines. Therefore, stress relief of coal seam has become an urgent technical demand for outburst prevention method in deep mines. In this study, based on zonal disintegration characteristics of deep surrounding rock, a regional strip outburst prevention method, called strip stress relief combined with gas extraction through stress‐relief floor roadway, was proposed, and relevant in‐site investigations were carried out in the Qujiang coal mine in China. Our results show that the zonal disintegration phenomenon occurs in the high‐stress surrounding rock at great depths, and induces the stress‐relief effect on the upper coal seam, in which the permeability and extraction radius of boreholes are increased greatly. The results of deformation and failure of surrounding rock of floor roadway show that from the surface to deep regions, fractured and nonfractured zones were alternatively distributed in the surrounding rock of deep floor roadways, the damage degree of surrounding rock was gradually weakened, and the width of fractured area was gradually reduced. The displacement of surrounding rock also presented the characteristics of alternative distribution of wave peak and trough. Moreover, the deformation and failure of surrounding rock presented a time‐dependent rheological behavior. In the stress‐relief zone, the coal seam permeability was enhanced significantly, with the maximum value being 43 times larger than that of the original coal seam. The effective gas extraction radius of the borehole was improved by 15%‐45%. During the driving period of coal roadways, the outburst risk prediction indexes K1 and S of the working face were lower than the critical value, and the driving speed of the coal roadway improved from 40 m per month to 100 m per month. This indicates that the proposed strip regional outburst prevention method can simultaneously reduce the ground stress and the gas content, and can effectively eliminate the outburst risk of coal roadway in deep mines.

CO2 presplitting blasting is an effective method to increase coal seams permeability and improve gas drainage efficiency. During the blasting process, the empty holes in the coal and rock mass have a significant effect on crack growth. In the experiment, a sample containing empty holes was used for CO2 presplitting blasting. The VIC‐3D was used to observe the change in the surface displacement of the sample; and the amplitude of the wave during the blasting process was collected using ultrasonic waves. Here, we calculated the attenuation coefficient α, analyzed the internal crack damage of the coal and rock mass, and compared the LS‐DYNA simulation results to analyze the empty hole effect on the crack growth of the coal and rock mass. The results show that: (a) radial tensile stress is generated due to the superposition of compression waves and reflected waves during blasting, resulting in an approximately straight main crack channel between the blast hole and the empty hole; (b) When both the stress and the attenuation coefficient reach their peaks, a main crack is formed and the most severe damage occurs inside the coal and rock mass; (c) the main crack channel was formed at 0.13 seconds, and the energy consumption reached the peak at 0.18 seconds, the negative linear correlation between energy and stress was obtained. Therefore, the empty hole effect provides a good guide for the crack propagation of the coal and rock mass and provides a new experimental scheme for increasing the permeability of coal seams.

High gas mines and outburst mines contribute to more than 30% of the coal production capacity in China. In view of this, coordinating the development and use of coal and gas has become an urgent concern for China's coal industry. After years of efforts, the concept of a co‐mining mode for coal and gas in China has gone through many stages, including theoretical discussion, engineering application, and assumption of concepts. Three modes have been gradually developed: the Huainan mode, based on pressure relief co‐mining of a protective layer; the Jincheng mode, based on directional long borehole co‐mining; and the YangQuan/SongZao mode, based on cross‐layer borehole co‐mining. These modes provide strong direction and the impetus to solve current predicaments and challenges of coal mining in China. Under the concept of “green” extraction and the corresponding urgent needs for environmental protection, high efficiency, and energy‐saving extraction, experts and scholars in the coal industry are also exploring development trends for coal in the future. For example, researchers have suggested idealized mining methods for replacing traditional mining methods, including fluidized mining technology, intelligent unmanned mining technology, precision mining technology, green development of abandoned mines technology, and mining based on other technical means.

A strong mining disturbance may cause the superposition of local stresses and serious disasters such as crushed supports and severely destroyed roadways. To study the distribution law of mining‐induced stress under hard roof conditions, an advance abutment pressure distribution model was developed. By monitoring the support pressure, a novel method of reckoning intensive factors was proposed, and then, the pressure distribution characteristics were obtained. An innovative in situ test of the mining‐induced stress increment was performed. At the Tongxin coal mine, the field monitoring of no. 8309 working face revealed the following. (a) The peak position of the fully mechanized working face with a hard roof was 5.9 m away from the mining face in which the average intensive factor K was 1.48. The pressure of the single props developed could be roughly divided into the fluctuation, slow increase, and stable stages. (b) A theoretical model of the stress evolution of the working face was proposed. Using an in situ uniaxial compression test, a law governing the variation of the advance abutment pressure was developed. The peak strength was reported to be 36 MPa, which is consistent with the advance prop pressure. (c) Mining‐induced stress violently fluctuated during the process of top coal caving; the K values in the supports in the middle of the working face and their rates of growth were apparently higher than those in the end supports. A Gaussian distribution of K was established for this phenomenon. The results obtained provide first‐hand data for safe and efficient mining under similar geological conditions.

Protective coal layer (PCL) mining is a preferred regional method for preventing coal and gas outbursts; stress‐relief of PCL mining is the prerequisite of pressure‐relief gas drainage. In order to study the stress‐relief effect of PCL mining on protected coal seams and determine the protection scope of PCL mining under different inclinations, this paper uses physical simulations to study the stress‐relief law and deformation characteristics of the strata during upper PCL mining with a gentle inclination (25°), an intermediate inclination (45°), and a steep inclination (65°). The results show that as the coal seam dip increases, the degree of deformation and failure of the overburden strata gradually decreases, the severe subsidence and expansion area of the overburden strata tends to gradually develop in the uphill direction of the working face, and the floor strata underlying the protective seam significantly expand toward the goaf. However, the absolute value of the upward movement of the floor strata is much smaller than that of the roof strata; and the greater the dip angle, the greater the ratio of floor displacement to roof subsidence. The stress‐relief curve of the protected layer is approximately U‐shaped. As the inclination of the coal seam increases, the stress‐relief range decreases gradually. The maximum relief‐stress and the stress release coefficient of the protected layer initially increase and then decrease. The stress concentration coefficient of the protected coal seam initially increases first and then decreases in both uphill and downhill of the working face in the PCL. As the inclination increases, the stress‐relief angle of the downhill boundary initially increases and then decreases, while the stress‐relief angle of the uphill boundary decreases gradually. Our research results provide guidance for the delimitation of the protected scope of PCLs with different dip angles.

Mountain railway alignment optimization is known as a very complex engineering problem that should consider many factors, such as drastically undulating terrain, geological hazard impacts,...

Protective seam mining is the preferred method for gas control and safe mining in high‐outburst coal seam groups. However, a hard‐thick sandstone roof (HTSR) triggers new gas problems when it covers directly above the first‐mined protective coal seam. To solve these problems, a typical case study in No. 12 Coal Mine was conducted. The simulation results indicate that the HTSR greatly prevents the plastic deformation of the upper roof formations without affecting the expansive deformation in the underlying protected seams. The pressure‐relief gas in protected seams will flow into the protective seam without continuing to migrate to roof strata, thereby turning the protective seam into a new high‐risk area. Therefore, roof presplitting (RPS) technology was proposed to effectively break the HTSR, create roof fracture passages, and divert the gob gas of the protective seam upward. Meanwhile, gob‐side entry construction (GSEC) was conducted to enhance gas discharge in the protective seam by adopting rapid filling, roof cutting, and active supporting technologies. Through the upper protective seam mining, RPS, and GSEC, gas migration passages were constructed step‐by‐step to divert the gas from high‐risk areas to low‐risk areas. As a key first step, gas diversion not only optimized the distribution of gas sources but also significantly reduced gas hazards. Source‐by‐source extraction was then performed to effectively control the high‐concentration gas in the newly formed gas source, further eliminating the mining risk. By applying the stepwise risk control method combined with gas diversion and extraction, the safe production was successfully achieved with excellent outburst prevention effects, and the gas extraction rate was significantly improved to more than 66%. This practice could be used for deep high‐gassy or high‐outburst coal seam group mining.

In this paper, we conducted a systematic study on the development characteristics and logging prediction of fractures of the Upper Paleozoic tight gas sandstone reservoirs in the eastern Ordos Basin. A new fracture prediction method was proposed based on the variable scale fracture probabilistic model. The calculation steps of this method were as follows: First, the sensitivity of each conventional log series to the tight sandstone fractures was analyzed. It was found that acoustic time difference (AC), density (DEN), natural gamma ray (GR), and deep investigate double lateral resistivity (RD) have good log responses to fractures. Then, the ratio of the range (R) to the standard deviation (S) of the log data was obtained. Finally, the second derivatives of the log series AC, DEN, GR, and RD were calculated, and a new fracture index was constructed (integrated second derivative, FC) using the multiple regression method. The fracture recognition rates of this method are distributed in 64.3%‐85.7%. Therefore, the constructed integrated second derivative (FC) based on conventional logs is effective to quantitatively characterize the fracture development of tight sandstone.

Due to the existence of abandoned roadways in the thick coal seam, the ground pressure would increase greatly due to the roof advanced breaking when the working face passed through the affected area of abandoned roadways. In order to solve this problem, a solution for roof presplit in the abandoned roadway was proposed. Based on the mining and geological conditions of Huasheng Hufeng coal mine, the roof vertical stress and vertical displacement with different roof presplit distance were analyzed by using FLAC3D numerical software. The research results indicated that the roof vertical stress and vertical displacement could be reduced effectively by roof presplit. When the roof presplit distance was 15 m, the maximum vertical stress and the maximum vertical displacement were both minimum. The maximum vertical stress was reduced by 14.55% and the maximum vertical displacement was reduced by 37.51% after roof presplit. The reasonable roof presplit distance of the working face was determined to be about 15 m by combining theoretical and numerical analysis. The engineering application results indicated that the maximum working resistance of the hydraulic support was reduced by 35.86% after roof presplit, and the engineering effect was good. The research results can provide technical guidance and theoretical support for the same type mines.

This paper endeavors to reveal the squeezing failure mechanism of roof‐coal masses and its correlation with the movement of the roof strata. An integrated method incorporating field instruments and numerical modeling was conducted. The borehole camera detection revealed that the development degree and scope of cracks in the roof strata on the coal pillar side are significantly larger than that on the panel rib side, and the fracture line of the main roof occurred above the coal pillar. A rigorous modeling procedure verified the borehole camera detection results and also found that the vertical and horizontal displacement of the roof‐coal mass exhibited asynchronous development characteristics at various heights. Subsequently, a comprehensive control strategy was proposed to prevent the squeezing failure behavior of roof‐coal masses in DUOS gob‐side entry. This study provides a basis for understanding the squeezing failure behavior of roof‐coal masses, and the proposed control strategy can potentially be applied in other similar mining projects.

With the increase of the coal mining depth, the surrounding rock shows characteristics of high stress and large deformation. However, the traditional bolt could not adapt to this surrounding rock environment and become invalid due to low elongation. In order to solve the problem, the new type of yielding bolt has been designed. It could release the deformation energy of the surrounding rock through its yielding pipe. However, few studies have been reported on the mechanism in bearing capacity decrease of the yielding pipe. Furthermore, the evaluation of the yielding bolt was not fully understood. Under such a background, a numerical model of the yielding model was established. According to the numerical simulation, the mechanism of the decrease in the bearing capacity of the yielding bolt is that the buckling occurs at different positions of the yielding pipe, making the material stiffness matrix turn negative, and the bearing capacity decreases significantly. Also, the performance of the yielding bolt could be evaluated from the use efficiency of the yielding pipe, the plastic strain characteristics of the components of the yielding bolt, and the energy absorption law. The evaluation results indicated that: (a) the deviation of the yielding pipe's Mises stresses was within the range of 1.0%‐4.0%. The stresses were distributed evenly, and the material use efficiency was high; (b) only the yielding pipe occurred the plastic failure during the yielding process, and other components were at the elastic stages. After the yielding, the yielding bolt was still effective for support. (c) The yielding pipe could absorb energy smoothly, which is helpful for the stability of the yielding bolt.