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Blasting roof cutting when the working face is directly covered with a hard roof can change the roof structure, which is an important factor for preventing dynamic disasters induced by hard roofs. This article used theoretical analysis to establish an expression for the distribution of the side abutment stress near the end of the working face before and after roof cutting. The stress reduction showed a power function growth trend with increasing crack zone height and a linear growth trend with increasing cantilever length of the hard roof. The results of the theoretical analysis provide a new approach for evaluating the effect of roof cutting and stress relief. The numerical simulation method was used to analyze the stress and plastic zone of the stope and the deformation characteristics of the roadway after roof cutting. The results showed that the advance and side abutment stresses of the working face decreased after roof cutting, and the range of the roof plastic zone increased. In addition, the displacements of the sides and floor of the roadway were reduced after roof cutting, which is beneficial for roadway stability control. Based on the research results, the roadway support scheme was optimized, and the advance support of the roadway was removed. This greatly reduced the work intensity and support cost and ensured the stability of the roadway. [ABSTRACT FROM AUTHOR]

The stability of the surrounding rock in the inclined coal seam stope is crucial for the safety of the gob-side entry. In this article, we systematically analyze the surrounding rock stability of the gob-side entry formed by roof-cutting (GEFR) in an inclined coal seam. We identify three forms of roof structure evolution in the formation process of GEFR and analyze the two main modules affecting the deformation of the surrounding rock structure. We determine the critical elements of surrounding rock deformation in different stages of the GEFR retaining process. Further, we propose a classification of the deformation of the surrounding rock structure of GEFR into stress and structural types during stabilization. We analyze the length of the gangue side's bearing area and calculate the lateral gangue's impact energy. We establish three instability modes of the roof based on the fractured state of the roof structure of the GEFR and provide a mechanical criterion of instability. Finally, based on the results of our theoretical analysis, we propose a control principle for the surrounding rock deformation of GEFR and establish countermeasures for controlling the roof-cutting angle and an asymmetric coupling support system. A field case study was conducted under conditions involving an inclined thick coal seam to investigate the surrounding rock deformation and overburden stress evolution using field monitoring data. The field test results confirm that the control measures of the control roof-cutting angle and the asymmetric coupling support system positively impact the stability of the surrounding rock of the roof-cutting entry in an inclined coal seam. [ABSTRACT FROM AUTHOR]

Abstract Taking the return-airway 4204 with roof cutting in Longquan Coal Mine as the engineering background, roof structure, key parameters, and deviatoric stress evolution were studied. Conclusion: The Key Stratum within a 4–8 times mining height is considered as Near Key Stratum. Cutting the roof makes it possible to form a cantilever structure of the Key Stratum on the solid coal side, which is more conducive to the stability of gob-side roadway. During cutting angle of 90–55°, the deviatoric stress increases linearly, and the increase rate is coal pillar > solid coal > roof > floor. While cutting length from 0 to 35 m, the deviatoric stress decreases linearly, and the decreasing range: coal pillar > solid coal > roof > floor. When coal pillar width is from 30 to 4 m, the deviatoric stress of left side and floor presents a “single peak” distribution. The deviatoric stress of coal pillar changes from an asymmetric “double peak” to a bell-shaped distribution, and the deviatoric stress of roof changes from a “single peak” to an asymmetric “double peak” distribution. Under same coal pillar width, the deviatoric stress of left, coal pillar and roof after roof cutting decreases most obviously, followed by the floor. Finally, the coal pillar width is 8 m, the cutting angle is 75°, the cutting length is 20 m, and the hole spacing is 1.0 m. The support scheme is bolt + metal mesh + steel belt + anchor cable combined support. The stable period of roadway is about 10 days.

In order to meet the needs of safe production in coal mines, many roadways are arranged in the bottom plate of coal seams, such as part of transportation alleys，drainage roadways, and gas extraction roadways. The mining stress generated by the working face causes the stress increase of the surrounding rock of the floor roadway through the transmission of the floor rock strata. It exacerbates the deformation of the surrounding rock of the floor roadway, which is easy to cause permanent support failure, roof sinking, dropsy at the bottom of the roadway, convergence of the two gangs, and other damages. In response to this, a control technology is proposed to implement hydraulic fracturing in the stress transfer path, creating a network of hydraulic fractures with a certain spatial pattern in the designated area, forming a fractured weak structural body, realizing stress transfer within the area, thus reducing the stress within the area of the roadway, and controlling the stability of the perimeter rock of the roadway, and through theoretical analysis and field engineering verification, the mechanical mechanism of stress transfer of weak structures in floor dynamic pressure roadway fracturing is revealed, the corresponding mechanical model is established, and the influence factors such as reasonable location and range of weak structures are solved. The results show that: ① Fracturing weak structure causes obvious changes in local stress field, and there are stress increasing zone and stress decreasing zone, and the stress decreasing zone is mainly distributed in the direction of the connection between weak structure and mining stress, mainly concentrated in an arch range; Due to the expansion effect, the stress concentration occurs in the vertical direction of the stress source, and the stress rise area appears. ② The magnitude of maximum principal stress change is related to the long axis L, short axis H, distance P to the roadway, horizontal angle β to the roadway line, strength C and internal friction angle α of the fractured layer, and damage variable D of the fracture in the weak structural body of the fracture. ③ The proposed method is used to design the pressure relief scheme of 103 belt concentrated roadway in Yuandian No. 1 Mine of Huaibei Mining Group. The engineering application results show that the deformation rate of roadway under dynamic pressure of floor is significantly reduced, and the rationality of the stress transfer model of fractured weak structure in roadway under strong dynamic pressure of floor is verified.

Abstract Automatic roadway formation by roof cutting is a sustainable nonpillar mining method that has the potential to increase coal recovery, reduce roadway excavation and improve mining safety. In this method, roof cutting is the key process for stress relief, which significantly affects the stability of the formed roadway. This paper presents a directionally single cracking (DSC) technique for roof cutting with considerations of rock properties. The mechanism of the DSC technique was investigated by explicit finite element analyses. The DSC technique and roof cutting parameters were evaluated by discrete element simulation and field experiment. On this basis, the optimized DSC technique was tested in the field. The results indicate that the DSC technique could effectively control the blast-induced stress distribution and crack propagation in the roof rock, thus, achieve directionally single cracking on the roadway roof. The DSC technique for roof cutting with optimized parameters could effectively reduce the deformation and improve the stability of the formed roadway. Field engineering application verified the feasibility and effectiveness of the evaluated DSC technique for roof cutting.

Abstract The gob‐side entry‐retaining by roof cutting and pressure relief (GERRC) method is an advanced no‐pillar mining method that can significantly improve coal recovery and reduce roadway accidents. However, according to case studies, there is relatively little research on the application of the GERRC method in geological conditions of soft rock formations (especially when the roof and floor are both mudstone), and such research is needed. Therefore, based on the typical soft strata of the Xinyi Coal Mine, this paper analyzes the failure mechanism of the roadways and proposes the GERRC method with coal rib and corner strengthened support (CRCSS). The evaluation indexes of the roof convergence rate and cable safety margin are established, and the effects of roof cutting and CRCSS on roadway deformation control are explored by a numerical comparison test. The results show that roof cutting has a limited effect on roadway deformation. The deformation can be reduced by 75.77% by implementing CRCSS on the basis of GERRC. Then, the evolution characteristics of roadway stress and deformation in the process of mining are further discussed through field contrast tests. The field application results show that compared with that of GERRC with conventional support, the surrounding rock deformation of GERRC with CRCSS is reduced by more than 55%, the safety margin of the cable is improved. The overpressure of the hydraulic prop is diminished, and the stability distance of the roadway is reduced by approximately 30%. Finally, this paper discusses the mechanism to control roadway deformation by CRCSS. This research expounds the rationality of CRCSS, and the results can provide a reference for other situations with similar geological conditions.

In the N00 coal mining method, one of the most critical issues is ensuring the safety of the entry behind the working face. To address this challenge, various roof control techniques, such as precise directional roof-cutting technology (PDRCT), constant-resistance cable supporting technology (CRCST), and dynamic pressure-bearing supporting technology (DPBST), have been developed. However, the design method for these technologies has not been clearly defined, resulting in a lack of theoretical basis for parameter selection. This paper seeks to address this gap by further studying the mechanisms of PDRCT, DPBST, and CRCST in the N00 coal mining method, and proposing corresponding mechanical calculation models, design ideas, and calculation methods for these technologies. The results reveal that the primary function of PDRCT is to expand the height range of the caved rock mass in the mined area, thus reducing the subsidence space of the high-level roof and mitigating the dynamic pressure effect of the entry surrounding rock. The height of the roof cutting is crucial to the design, and its theoretical value must satisfy the condition that the broken expansion volume of the caved rock mass is equal to the volume that is mined. DPBST is essential for protecting the entry immediate roof and preventing internal damage during the movement of the upper roof. The dynamic pressure-bearing support strength should be appropriately designed to prevent the short cantilever roof structure from breaking within the entry's width during the movement of the high-level roof. Similarly, CRCST's most critical function is to maintain the long-term stability of the entry immediate roof by relying on the cable support forces and the stability properties of the high-level roof strata while it is not moving. The anchor cable support strength should be reasonably designed to prevent the short cantilever roof structure from collapsing under its own gravity. The proposed design method was applied to the Ningtiaota coal mine, leading to a 15.6% reduction in maximum roof deformation and a 12.0% decrease in average deformation, demonstrating the favorable impact of the approach. Highlights: The mechanisms of precise directional roof cutting technology (PDRCT), constant-resistance cable supporting technology (CRCST), and dynamic pressure-bearing supporting technology (DPBST) in the N00 coal mining method were revealed. Corresponding mechanical calculation models, design ideas, and calculation methods for the key parameters of PDRCT, DPBST, and CRCST were obtained. [ABSTRACT FROM AUTHOR]

Hard roof's 3D breaking characteristics is vital for mining pressure control. However, the research concerning a longwall face that employs an innovative roof-cutting technology via a chainsaw arm machine (RCTCAM) is scant. To address this gap, this paper thoroughly analyzes RCTCAM's core equipment and roof-cutting procedures. Firstly, the thin elastic plate theory and the superposition principle were applied to establish the first and periodic break mechanical models of hard roofs using the RCTCAM. These mechanical models elucidated the distribution laws of the first and third principal bending moments in a hard roof. Following this, based on tensile failure criteria and crack expansion criteria, the study uncovered that the hard roof's first break transitioned from an 'O–X' shape to a 'U–Y' shape, while its periodic break morphed from a 'C–ン' shape to an 'L–ノ' shape. This transformation led to a unique phenomenon. The rotation of arc-shaped triangular plates formed during the 'O–X' and 'C–ン' -shaped breaks resulted in severe damage to a gob-side roadway. However, a longwall face employing the RCTCAM did not produce such plates, effectively avoiding the associated damage. By implementing the RCTCAM in Workface 8311 of the Yanya Mine in China, the stress peaks of the coal pillars were reduced on average by 22.8%, and the deformation of the roadway decreased by 27.8%. These findings underline the success of the RCTCAM in achieving pressure relief for a gob-side roadway. Highlights: It was given that the theoretical calculation method for deflection, bending moment, and stress of a hard roof with the RCTCAM under the first and periodic breaks. When with the RCTCAM, hard roof's first break exhibits a transition from an 'O-X' shape to an 'U-Y' shape, while its periodic break changes from a 'C-ン' shape to an 'L-ノ' shape. Due to rotation of arc-shaped triangular plates formed in the 'O-X' and 'C-ン'-shaped breaks, a gob-side roadway bear severe damage. However, a longwall face with the RCTCAM has no such plates, thus avoiding damage. With the RCTCAM in Workface 8311 of the Yanya Mine, China, the stress peaks of a gob-side roadway's coal pillars dropped averagely by 22.8%, indicating that the RCTCAM achieve pressure relief for a gob-side roadway. [ABSTRACT FROM AUTHOR]

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Automatic roadway formation by roof cutting is a sustainable nonpillar mining method that has the potential to increase coal recovery, reduce roadway excavation and improve mining safety. In this method, roof cutting is the key process for stress relief, which significantly affects the stability of the formed roadway. This paper presents a directionally single cracking (DSC) technique for roof cutting with considerations of rock properties. The mechanism of the DSC technique was investigated by explicit finite element analyses. The DSC technique and roof cutting parameters were evaluated by discrete element simulation and field experiment. On this basis, the optimized DSC technique was tested in the field. The results indicate that the DSC technique could effectively control the blast-induced stress distribution and crack propagation in the roof rock, thus, achieve directionally single cracking on the roadway roof. The DSC technique for roof cutting with optimized parameters could effectively reduce the deformation and improve the stability of the formed roadway. Field engineering application verified the feasibility and effectiveness of the evaluated DSC technique for roof cutting. Highlights: A directionally single cracking (DSC) technique for roof cutting in automatic roadway formation of the non-pillar mining method is proposed. The mechanism of the DSC technique to achieve single cracking relies on effective control of the blast-induced stress. DEM simulation and field experiments are effective methods to evaluate the DSC and roof cutting parameters to improve the stability of the roadway surroundings. [ABSTRACT FROM AUTHOR]

Abstract Gob‐side entry formation by roof cutting is a new technology for no pillar coal mining, which can maximize coal resources and reduce roadway drivage ratio. However, the mechanical behavior of the formed entry is complex while it is crucial to ensure the stability of the entry for mining safety. This paper proposed a machine learning‐based method for predicting the stability of the formed entry, which combined artificial neural network (ANN) with particle swarm optimization (PSO) algorithm or genetic optimization (GO) algorithm. The data set from 75 coal mining faces from 2009 to 2022 was employed to train and test the models. A descriptive variable of dynamic unstable distance was introduced to evaluate the stability state of the formed entry and six other parameters were chosen as influence parameters. The two intelligent models were compared with each other to have a comprehensive assessment. Model assessment indices such as R2, mean absolute error, mean absolute percentage error, and root mean square error were used to evaluate the accuracy of the models. The results of both developed models are promising, and the predictive accuracy of the PSO‐ANN model is higher than that of the GO‐ANN model. Through sensitivity analyses, it has been found that the coal seam thickness and roof rock hardness are the most important parameters for influencing entry stability. The developed method provides a practical tool for the prediction of entry stability and the optimization of entry design.

In order to solve the problem of stress concentration on the roof of the mining trench, reduce the risk of sudden collapse of the roof overburden and disturbance, improve the control effect of the surrounding rock of the roof cutting and retaining roadway, and reduce the construction cost of mining tunnels, a new type of pouch sealing technology has been developed. By using on-site testing methods, the optimal sealing material ratio was optimized, and the crack propagation law and roof cutting effect of the 11503 W working face in Zhaizhen Coal Mine, Shandong Province were studied under hole spacing of 0.7, 1.0, and 1.1 meters and different sealing methods. The results show that using 1.5 m single pouch sealing technology in the blasting test, when the water cement ratio of the sealing material is 1:1, the required sealing strength and sealing temperature can be achieved, and there will be no punching phenomenon. When the spacing between holes is 1 m, the blasting effect is optimal, with a single hole effectively reaching a cutting seam length of about 0.5 m. There are obvious through cracks in the cave, with a total length of about 7 meters. After using the new pouch sealing technology for blasting, the displacement and bottom drum volume on both sides of the tunnel are lower than those of the traditional yellow mud sealing method, and the bottom drum volume is reduced by 37% and 53%, respectively. Based on comprehensive theoretical analysis and on-site experiments, the optimal hole spacing is determined to be 1 m, and the pouch sealing effect is good.

With the increase of coal seam mining thickness, the caving height of stope roof, the mining-induced stress increase, and the control difficulty of gob-side entry retaining increase. To apply the gob-side entry retaining (GER) technology in thick coal seams, optimize the support method and reduce the deformation, based on directional energy-gathering blasting technology and roadside filling technology, gob-side entry retaining with synergistic roof cutting and roadside filling (GER-RCRF) is proposed. Through theoretical analysis, numerical simulation and field experiments, the mechanism and effect of the method are analyzed. The results show that due to the stress relief of roof cutting, the pressure of the solid coal rib and the roadside filling of the GER-RCRF is reduced, and the stress concentration area shifts to the deep rock mass. Under the condition of roof cutting, the stress of roadside filling is distributed in a "single peak", and with the width increases, the peak stress first increases and then decreases, and then increases and then decreases. Meanwhile, the roof cutting height should be based on the broken and expansion effect of the rock strata, considering the key stratum effect of the rock layer. The stress of the surrounding rock is further reduced when the overlying key strata is cut off. Finally, the GER-RCRF has successfully reduced the stress of roadside filling, roof and solid coal rib, optimized the stress environment of surrounding rock, and successfully realized the purpose of gob-side entry retaining. The field test verified the effectiveness of GER-RCRF. The stress of roadside filling and the deformation of surrounding rock are significantly reduced. The research results provide a certain degree of scientific basis for the successful application of gob-side entry retaining in thick coal seam. Highlights: Gob-side entry retaining with synergistic roof cutting and roadside filling (GER-RCRF) method is proposed based on directional energy-gathering blasting technology and roadside filling technology. Roof cutting can reduce the pressure of roadway surrounding rock, and roadside filling can support roof. The synergistic effect of the two can optimize the stress environment and reduce the deformation of surrounding rock. Comprehensive monitoring showed that GER-RCRF method effectively realizes the gob-side entry retaining in thick coal seam, meanwhile, reduces the deformation of surrounding rock and the stress of roadside filling. [ABSTRACT FROM AUTHOR]

The gob‐side entry‐retaining by roof cutting and pressure relief (GERRC) method is an advanced no‐pillar mining method that can significantly improve coal recovery and reduce roadway accidents. However, according to case studies, there is relatively little research on the application of the GERRC method in geological conditions of soft rock formations (especially when the roof and floor are both mudstone), and such research is needed. Therefore, based on the typical soft strata of the Xinyi Coal Mine, this paper analyzes the failure mechanism of the roadways and proposes the GERRC method with coal rib and corner strengthened support (CRCSS). The evaluation indexes of the roof convergence rate and cable safety margin are established, and the effects of roof cutting and CRCSS on roadway deformation control are explored by a numerical comparison test. The results show that roof cutting has a limited effect on roadway deformation. The deformation can be reduced by 75.77% by implementing CRCSS on the basis of GERRC. Then, the evolution characteristics of roadway stress and deformation in the process of mining are further discussed through field contrast tests. The field application results show that compared with that of GERRC with conventional support, the surrounding rock deformation of GERRC with CRCSS is reduced by more than 55%, the safety margin of the cable is improved. The overpressure of the hydraulic prop is diminished, and the stability distance of the roadway is reduced by approximately 30%. Finally, this paper discusses the mechanism to control roadway deformation by CRCSS. This research expounds the rationality of CRCSS, and the results can provide a reference for other situations with similar geological conditions. [ABSTRACT FROM AUTHOR]

The untimely collapse of the lateral cantilever structure is one of the main factors in the deformation of the surrounding rock in hard-roof mines. In this study, a method for weakening the hard roof using dense drilling is proposed to promote roof collapse. Based on the geological engineering conditions in the Tashan coal mine, an FLAC3D numerical model was developed by considering the plastic-softening characteristics of the hard roof to investigate the dynamic evolution process of the weakening roof surface. As the load increased, failure around drillings occurred gradually, and the failure zones expanded in an x-shape from the drillings toward each other, forming a weakened macro-surface. The influence of the drilling arrangement on weakening the hard roof was investigated using numerical models of various drilling diameters and spacings. The results indicated that a large diameter or small spacing was helpful for the formation of a weakened macro-surface. However, differences were observed in the response of key parameters to the weakening effect. The peak stress, fracture stress, and energy absorbed during loading and dissipated during the rock failure process displayed a downward trend for all models with an increasing drilling diameter. In contrast, these parameters, except for the fracture stress, tended to increase with a decreasing spacing. Field monitoring revealed that the average rock strength around dense drillings decreased from 69.0 to 60.5 MPa during the advancing of the work face after roof cutting by implementing dense drillings. Furthermore, the maximum axial tension increments of the cable and bolt reached 80 kN and 10 kN, respectively. Highlights: A roof-cutting method involving dense drillings to weaken hard roofs was proposed. The progressive failure mechanism of the rock around dense drillings was investigated. The influence of the drilling arrangement on weakening hard roofs was investigated. The effectiveness of the roof-cutting method was revealed by conducting a case study. [ABSTRACT FROM AUTHOR]

Shearer is an essential equipment in mechanized coal mining process. Roof cutting often turns up for shearer during working process, leading to extra vibration on shearer and reducing its service life. Coal and rock interface recognition is a fundamental technical way for shearer to avoid continuous roof cutting. In this paper, an effective method for coal and rock interface is proposed and it is mainly based on the cutting loads on shearer drum in three different kinds of working states. The constitutions of cutting force on shearer drum are analyzed under conditions of different proportions of rock thickness in the cutting range and then model for calculation of cutting force in the coal–rock mixed seam are proposed which is a function of rock proportion in the cutting range. To verify the model, hard roof with different material strengths and different interfaces are established with the numerical method and rock proportions in the cutting range are derived based on the mentioned method. In terms of the situations where rock material properties are close to coal and the results are obtained with lower accuracy, enlarging the difference of rock proportions in the second and third states is proposed and the relations between the recognition accuracy and the differences of rock proportions in different states are explored as well. The results show that the estimation method works well with qualititative analysis of coal and roof interface even if coal and rock material properties are various and not able to be known in advance. In addition, the adjustment height of shearer drum is the important factors highly related with the estimation accuracy and it would be helpful for accuracy improvement in conditions where the material properties of coal and roof are closer to each other or larger roof cutting thickness happens in coal mining. The method provides the possibility for qualititative analysis of coal and roof interface with easy accessibility and wide adaptability. [ABSTRACT FROM AUTHOR]

The deformation and failure mechanism of surrounding rock and the control measures under the condition of long-time high superimposed stress are the keys to gob-side entry retaining support technology in thick coal seam with soft bottom. The existing research on the deformation and failure mechanism of surrounding rock and support control of gob-side entry retaining in thick coal seam is mainly aimed at deformation of roof and side of gob-side entry with hard rock bottom, and the strength of filling body and material proportion. There are few research on retaining roadway with soft bottom in thick coal seam. The mechanical analysis of gob-side entry retaining is incomplete, and the support scheme is single. In order to solve the above problems, taking N1303 working face of Gucheng Coal Mine of Shanxi Lu'an Chemical Industry Group Co., Ltd. as the engineering background, the failure mechanics models of roof, coal wall and floor are established. The deformation and failure characteristics of the roadway surrounding rock are analyzed. The roof is in a mixed stress environment, which is prone to tensile failure. Under the action of high stress, the solid coal side suffers compression shear failure, and the anchor rod fails. The filling body intrudes into the floor under pressure, causing the floor to tilt and lose stability, which is prone to soft coal broken and swelling. According to the deformation and failure characteristics of surrounding rock, the trinity surrounding rock support control scheme is proposed, namely, controlling the roof, restricting the coal side and yielding floor. In order to ensure that the roof can balance the stress distribution above the gob-side entry retaining, the method of anchor cable + filling body top cutting is adopted. Thus the roof does not form a cantilever beam structure above the roadway, only sinking occurs, and there is no rotary deformation. Considering the roof stability of gob-side entry retaining, the way of grouting anchor cable is adopted to grout the broken roof of the roadway to form a whole for better controlling the roof. In order to improve the support strength of the solid coal side, short anchor cables are added to connect the coal seam in the limit equilibrium area with the deep elastic bearing layer, and reduce the support resistance of the filling body beside the roadway. The proper yielding of the floor is beneficial to the flexible support of the whole roadway. The floor is reinforced by digging grooves and pouring strip foundations under the filling body wall. The original gob-side entry retaining support scheme is optimized by using the trinity surrounding rock support control scheme. The field test results show that after using the optimized support scheme, the roof movement subsidence is reduced from 337 mm to 142 mm, and the coal side movement is reduced from 305 mm to 70 mm. The floor movement is reduced from 675 mm to 162 mm, and the roadway convergence rate is reduced from 34.1% to 10.73%. The working resistance of the anchor rod (cable) is stable, the filling body is free of damage and inclination, and the support effect is good.

Gob‐side entry formation by roof cutting is a new technology for no pillar coal mining, which can maximize coal resources and reduce roadway drivage ratio. However, the mechanical behavior of the formed entry is complex while it is crucial to ensure the stability of the entry for mining safety. This paper proposed a machine learning‐based method for predicting the stability of the formed entry, which combined artificial neural network (ANN) with particle swarm optimization (PSO) algorithm or genetic optimization (GO) algorithm. The data set from 75 coal mining faces from 2009 to 2022 was employed to train and test the models. A descriptive variable of dynamic unstable distance was introduced to evaluate the stability state of the formed entry and six other parameters were chosen as influence parameters. The two intelligent models were compared with each other to have a comprehensive assessment. Model assessment indices such as R2, mean absolute error, mean absolute percentage error, and root mean square error were used to evaluate the accuracy of the models. The results of both developed models are promising, and the predictive accuracy of the PSO‐ANN model is higher than that of the GO‐ANN model. Through sensitivity analyses, it has been found that the coal seam thickness and roof rock hardness are the most important parameters for influencing entry stability. The developed method provides a practical tool for the prediction of entry stability and the optimization of entry design. [ABSTRACT FROM AUTHOR]

The longwall mining method with gob-side entry retaining via roof cutting is a new underground coal mining method which has the characteristics of a high resource recovery ratio and environmental friendliness. Due to the complexity of this method, the research method of case-based dynamic on-site monitoring, analysis, adjustment, and optimization is usually adopted. Based on a roadway retaining via roof cutting project, in addition to the traditional indirect monitoring method of hydraulic support pressure, this study innovatively establishes a direct monitoring method for roof caving by monitoring the gangue pressure in the goaf, which provides data for the roof cutting effect and offers a new method for studying the overlying strata movement. In the project, a comprehensive monitoring and analysis system was established, including gangue pressure, cable bolt stress, bracket pressure, roadway deformation, and roof separation, which was used to dynamically analyze the effect of roof cutting and optimize the support design. The results show that the pressure of the hydraulic support close to the roof cutting is low, indicating that roof cutting is favorable in the roadway retaining mining method. The roadway deformation in the advanced abutment pressure area of the working face is small. The mining-induced stress caused by the collapse and compaction of the overlying strata in the goaf is the dominant factor affecting the effect of roadway retaining, especially in the 50–100 m range behind the working face, where the dynamic load causes high bearing capacity of the support elements, large roadway convergence, and roof separation. Temporary support and supplementary reinforcement should be added when necessary. The monitoring system presented in this study is highly comprehensive, simple, reliable, and low in cost, providing a reference for roof cutting roadway retaining projects and roof caving-related studies. [ABSTRACT FROM AUTHOR]

Pre-driven longwall retracement roadway (PLRR) is commonly used in large mine shaft. The support crushing disasters occur frequently during the retracement, and roof management is necessary. Taking the 31107 panel as research background, the roof breaking structure of PLRR is analyzed. It is concluded that the roof cutting with vertical hydraulic fracture (HF) at a specified position, that is, fixed-length roof cutting, can reduce support load and keep immediate roof intact. The extended finite element method (XFEM) is applied to simulate hydraulic fracturing. The results show that both the axial and transverse hydraulic fracturing cannot effectively create vertical HFs. Therefore, a novel construction method of vertical HF based on the stress shadow effect (SSE) is proposed. The stress reversal region and HF orientation caused by the prefabricated hydraulic fracture (PF) are verified in simulation. The sub-vertical HFs are obtained between two PFs, the vertical extension range of which is much larger than that of directional hydraulic fracturing. The new construction method was used to determine the field plan for fixed-length roof cutting. The roof formed a stable suspended structure and deformation of the main PLRR was improved after hydraulic fracturing.

Improving coal resource mining rates has long been a focus of coal industry research. The gob-side entry retaining by roof cutting (GERRC) is a new coal mining technology that has gained popularity in China due to its high mining rate and safety. Based on the GERRC technology, the precise technical procedure is elaborated, and the fundamental idea of pressure relief is explored through creating a structural mechanics model of the surrounding rock in this paper. The results of mechanical analysis show that the primary mechanism of roof pressure release is to weaken the integrity of the roof, thereby reducing the ultimate bending moment of the rock stratum. In addition, an additional strategy for pressure release is suggested in this research, involving the weakening of the roof rock by the creation of dense pressure-released holes. The results of the engineering field experimentation demonstrate that the dense pressure-released holes can completely replace the conventional blasting technology of the past to achieve the effect of releasing the roof pressure, thus avoiding the use of hazardous and challenging-to-obtain explosives and demonstrating safety, reliability, and feasibility. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Mine Automation is the property of Industry & Mine Automation Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The roof in a fully-mechanized face of a shallow coal seam with large mining height is prone to form a combined cantilever—articulated rock beam structure. When the support resistance is insufficient, the articulated rock beam will sink. This will make the combined cantilever beam rotate and fracture. It is then easy to induce the sliding and instability of the articulated rock beam, which results in large-scale roof cutting and the support crushing. Taking the combined cantilever beam structure as the main research object, and considering the mining damaged characteristics of cantilever beam rock stratum, the rock beam was regarded as a finite plate model with an edge crack of arbitrary dip angle. In addition, a fracture mechanics model controlled by a set of structural planes was established, the instability conditions of rock beam and the main control factors were analyzed, and the method of determining the support resistance were discussed. The results show that the cantilever beam rotates and fractures. This causes a chain reaction of the rock beam that leads to fracture. The combined cantilever beam then loses stability with the increase of the length of the crack length and the crack dip angle, and therefore it is easier to penetrate the cantilever beam and cause roof instability. The necessary condition for rock beam instability was crack activation, and the sufficient condition was the airfoil branch crack propagate through the rock beam. The influence degree of each parameter on the support resistance was thus determined: crack length a > crack dip angle β > rock thickness h > weighting interval l. The theoretical analysis results were proven to be reasonable by an in situ monitoring example of no. 22,310 working face in the Daliuta coal mine, China. On this basis, the reasonable value of support resistance was obtained. The conclusions of this research provide a new method for researching the roof instability mechanism. They are also conducive to the green and sustainable development of mines.

In this paper, roof-cutting technology of directional energy-cumulative presplitting blasting is taken as the research object. Through the numerical simulation software Ansys/Ls-dyna3D, the process of energy-cumulative blasting and non-cumulative blasting is simulated and analyzed by using the ALE algorithm. Moreover, the evolution processes of tensile strain energy, detonation stress wave of explosives, stress state of rock mass, and rock crack damage cumulative are compared in two conditions. In the energy cumulative state, the detonation wave acts centrally on the hole wall in the energy cumulative direction to form an initial crack, and then under the action of the jet of energy cumulative, the crack continues to propagate until it runs through. In the non-energy cumulative state, the crack propagates uniformly around the hole wall, forming irregular short cracks. The simulation is verified by the field test, and the law of crack propagation is the same with the simulation. Therefore, directional energy-concentrated presplitting blasting has good practicability in a roof presplitting operation. [ABSTRACT FROM AUTHOR]

To address the large deformation of goaf-side entries resulting from intense dynamic pressure, a method involving automatically retained entry by roof cutting pressure relief (ARERC) technology is proposed for use in thick and hard main roof longwall top coal caving (THLTCC) panel. Both physical and numerical model experiments have been conducted to verify the effectiveness of ARERC technology in controlling deformation. The evolution laws of stress and deformation in the surrounding rocks of the retained entry and the mechanism of pressure relief by roof cutting are analyzed. Results indicate that this technique optimizes the roof structure of the roadway and interrupts roof stress transfer between the retained entry and goaf. Consequently, the maximum vertical stress on the roof-cutting side of the retained entry roof is generally lower than on the uncut side. The retained entry deformation undergoes four distinct stages behind the panel: the pressure relief stage, deformation stage, compaction stable stage and stabilization stage. Notably, the deformation stage exhibits the highest deformation rate for the roadway. Therefore, it is recommended to utilize single hydraulic props for temporary support during the deformation stage to prevent damage to the retained entry caused by dynamic pressure disturbance. Based on the above analysis, several recommendations are provided for the field application of ARERC technology. Finally, the results from engineering application show the effectiveness of ARERC technology in controlling the deformation of the goaf-side entry. This ARERC technology can be extended to other coal mines with similar geological conditions. [ABSTRACT FROM AUTHOR]

Automatically formed roadway (AFR) by roof cutting with bolt grouting (RCBG) is a new deep coal mining technology. By using this technology, the broken roadway roof is strengthened, and roof cutting is applied to cut off stress transfer between the roadway and gob to ensure the collapse of the overlying strata. The roadway is automatically formed owing to the broken expansion characteristics of the collapsed strata and mining pressure. Taking the Suncun Coal Mine as the engineering background, the control effect of this new technology on roadways was studied. To compare the law of stress evolution and the surrounding rock control mechanisms between AFR and traditional gob-side entry driving, a comparative study of geomechanical model tests on the above methods was carried out. The results showed that the new technology of AFR by RCBG effectively reduced the stress concentration of the roadway compared with gob-side entry driving. The side abutment pressure peak of the solid coal side was reduced by 24.3%, which showed an obvious pressure-releasing effect. Moreover, the position of the side abutment pressure peak was far from the solid coal side, making it more beneficial for roadway stability. The deformation of AFR surrounding rock was also smaller than the deformation of the gob-side entry driving by the overload test. The former was more beneficial for roadway stability than the latter under higher stress conditions. Field application tests showed that the new technology can effectively control roadway deformation. Moreover, the technology reduced roadway excavation and avoided resource waste caused by reserved coal pillars.

• Fracture evolution in dual gob-side entries varies spatially and temporally. • A formula to calculate arbitrary dip rock layer cutting angles was derived. • A technology based on the fracture evolution's turning points was proposed. • Differential roof cutting-anchor grouting boosts stability in dual gob-side entries. The coal pillar-free gob-side entry retention technology (GER), which enhances resource recovery rates and reduces the amount of tunnel excavation, has been applied in multiple mining areas in China. However, cases of implementing gob-side entry retention on both sides of a single working face are rare. The asynchronous extraction of long-distance working faces leads to significant differences in the stress environment of roadways on both sides, and uniform technical means are poorly adapted to the control of surrounding rock on both sides, affecting the safe and efficient production. This paper, taking the dual gob-side entry retention on both sides of the 61001 W working face with thick mudstone roofs in Zhao Guan Coal Mine, Shandong Province, as the engineering background, utilizes a combination of theoretical calculations, numerical simulations, and on-site detailed monitoring to analyze the uncoordinated deformation characteristics of the upper part bulging and the lower part concaving of the two roadways. It clarifies the differentiated spatiotemporal evolution law of the number of fractures and the development turning points at different depths of the surrounding rock of the two entries, revealing the differential deformation mechanism of the surrounding rock of the two entries caused by stress state and fracture development differences. A "cutting roof to relieve pressure-multilevel continuous anchor-grouting" combined control technology system is proposed. By cutting off the stress transmission of the roof through drilling and blasting, and then reconstructing the integrity of the surrounding rock and improving the rock strength with the help of anchor-grouting. With the application of this new technology, the deformation of the surrounding rocks of the two entries was reduced by more than 60 % and 29 %, respectively, and the maximum crack depth of the roof was controlled within 3 m, significantly enhancing the stability of the roadways. The research results of this paper provide a reference for the control of surrounding rock in gob-side entry retention under similar conditions. [ABSTRACT FROM AUTHOR]

In the gob-side entry retaining by roof cutting (GERRC) technique, pressure is offloaded via directional roof cutting, and a roadway is automatically formed due to the ground pressure and rock-breaking expansion. To improve the application of the theory and technical system of GERRC in the Karst area in Southwest China, this research studies the key technology of GERRC in a high gas outburst coal seam, based on the engineering background of the 39114 working face of the Honglin coal mine. According to the geological conditions of the 39114 working face, by means of formula calculation, UDEC numerical modeling, and on-site drilling peeping, the optimal roof-cutting parameters suitable for the 39114 working face were determined: the roof cutting height was 7 m, the roof cutting angle was 15°, and the spacing of pre-splitting blasting holes was 600 mm. Additionally, the above roof-cutting parameters have achieved good results in the engineering practices of the 39114 transportation roadway, which shows that the technology of GERRC is feasible in high gas outburst mines and achieves the goal of safe and efficient mining. [ABSTRACT FROM AUTHOR]

The problem of strong ground pressure caused by thick and hard roofs in coal mine stopes has become more prominent. Blasting roof cutting and pressure relief are effective technical ways to solve this engineering problem. The key to achieving roof cutting and pressure relief is the evolution and penetration of cracks between blasting roof cutting holes in a mining stress environment. To solve this problem, research on the evolution of cracks between blasting roof cutting holes in a mining stress environment is being conducted. Along with specific engineering examples, the mechanical effect of blasting dynamic load in the surrounding rock medium between holes in a mining stress environment is analyzed using the research methods of field investigation, blasting simulation, and mechanical analysis. The fracture evolution law between blasting roof cutting holes under the conditions of different hole diameters and spacings, confining pressure environments, and rock mass strengths is analyzed using the univariate comparative analysis method. The research shows that the superposition effect of blasting dynamic load between adjacent blastholes in the transmission process leads to the "X" type penetration evolution of surrounding rock fracture area and fracture area between blastholes. Among them, the blasting effect of a hole diameter of 70 mm and a hole spacing of 0.8 m is best. When designing the blasting roof cutting scheme, we should pay attention to the key factors such as hole diameter and hole spacing. The hole spacing is particularly critical to the effect of roof cutting and crack formation, whereas the confining pressure and rock mass strength have little impact on the expansion and development of blasting cracks, which can be listed as secondary factors for comprehensive analysis in design. According to the transmission law of blasting dynamic load between holes, the critical criterion of blasting top clearance penetration under mining stress environment is deduced. Four important factors affecting blasting top cutting effect are simulated and studied for optimizing the design of roof cutting scheme. Practical engineering application results show that the blasting roof cutting scheme achieves a good seam- forming effect and creates good initial conditions for thick and hard roof cutting. It can serve as a reference for the decision making of blasting top caving technology under similar engineering conditions. [ABSTRACT FROM AUTHOR]

Based on the application of the retained gob-side entry in a fully mechanized face E2307 headgate, the stress distribution and deformation characteristics of the roadside backfill body for different types of roof cutting were investigated in this study by employing a combination method of theoretical analysis, numerical simulation, and field measurement. The study uses RocLab software to accurately modify the lithology of the simulation area, discuss the position of roof cutting and the pressure relief parameters of roof cutting, and select the optimal solution of the roof-cutting plan. The results show that the advanced pre-cracking effectively blocks the stress transmission in the high-level roof strata; the roadway is in the stress unloading zone, the stress environment of the surrounding rock in the roadway is significantly optimized, and the deformation of the surrounding rock in the roadway is significantly reduced. In the roof-cutting scheme, the deformation of the surrounding rock in the 90° main roof-cutting scheme is reduced by 78% compared with the uncut roof and by 39% compared with the 90° immediate roof cutting. The research results were successfully applied at the E2307 headgate of the Gaohe coal mine; the maximum roof subsidence and the maximum rib convergence were 121 and 74 mm, respectively. Field monitoring indicates that the deformation of the retained entry was controllable, and the final retaining effects were good.

The longwall mining method with gob-side entry retaining via roof cutting is a new underground coal mining method which has the characteristics of a high resource recovery ratio and environmental friendliness. Due to the complexity of this method, the research method of case-based dynamic on-site monitoring, analysis, adjustment, and optimization is usually adopted. Based on a roadway retaining via roof cutting project, in addition to the traditional indirect monitoring method of hydraulic support pressure, this study innovatively establishes a direct monitoring method for roof caving by monitoring the gangue pressure in the goaf, which provides data for the roof cutting effect and offers a new method for studying the overlying strata movement. In the project, a comprehensive monitoring and analysis system was established, including gangue pressure, cable bolt stress, bracket pressure, roadway deformation, and roof separation, which was used to dynamically analyze the effect of roof cutting and optimize the support design. The results show that the pressure of the hydraulic support close to the roof cutting is low, indicating that roof cutting is favorable in the roadway retaining mining method. The roadway deformation in the advanced abutment pressure area of the working face is small. The mining-induced stress caused by the collapse and compaction of the overlying strata in the goaf is the dominant factor affecting the effect of roadway retaining, especially in the 50–100 m range behind the working face, where the dynamic load causes high bearing capacity of the support elements, large roadway convergence, and roof separation. Temporary support and supplementary reinforcement should be added when necessary. The monitoring system presented in this study is highly comprehensive, simple, reliable, and low in cost, providing a reference for roof cutting roadway retaining projects and roof caving-related studies.

Triaxial hydraulic fracturing experiments were used to study the initiation pressure variation and acoustic emission characteristics of different guide seams sizes during roof hydraulic fracturing. Numerical simulations were used to explore the feasibility of multiple boreholes with prefabricated guide seams. An experiment of hydraulic fracturing on a pillar-free working face was also carried out in a coal mine. The results show that the specimens with guide seams reduced the initiation pressure, with the number of acoustic emission events and initiation pressure being inversely proportional to the size of the guide seams. Specimens without guide seams were deflected by stress and produced multi-level cracks, while the specimens with guide seams did not produce large secondary cracks and deflection. When the stress difference was small, three holes penetrated but not under large stress differences. The hydraulic fracturing technology of prefabricated longitudinal guide seams was tested in the Ningtiaota Coal Mine, and the auxiliary transportation roadway of S1201 working face was successfully retained for reuse in adjacent working faces. [ABSTRACT FROM AUTHOR]

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• A new RCAWC method is proposed based on characteristics of rock. • Analyzed the blocking effect of different roof cutting heights on mining pressure. • Comprehensive monitoring showed that RCAWC method efectively protects roadways. After the extraction of deep coal resources, the original stress state is disrupted, leading to increased abutment stress ahead of the working face. This heightened pressure causes significant deformation in the roadway preceding the working face. To tackle this issue, a pioneering method called Roof Cutting in Advance of the Working Face(RCAWC) has been introduced to mitigate deformation by proactively alleviating pressure. This method leverages the principle of conservation of energy within the rock mass system, augmenting the fragmentation energy of the roof rock mass through controlled blasting. This process aims to release the accumulated energy within the rock mass, thereby reducing pressure. This research not only elucidates the mechanism employed by RCAWC to counteract mining pressure but also delineates the evolving pattern of bearing pressure at various RCAWC heights. The findings reveal a shift in the abutment stress curve from a single-peaked to a double-peaked pattern after roof cutting. Notably, there is a significant reduction in abutment stress as the RCAWC height increases. However, as the thick roof is cut off, the negative correlation effect diminishes. Subsequently, an engineering implementation was carried out. Following the adoption of RCAWC technology, roadway deformation decreased by 63.6 % to 75 %, and the size of the protective coal pillar reduced by approximately one-third. These findings underscore the remarkable effectiveness of RCAWC technology in impeding the propagation of mining pressure towards roadways, reducing the extent of abutment stress, and ultimately alleviating stress and deformation within the surrounding rock formation. [ABSTRACT FROM AUTHOR]

In the gob-side entry retaining by roof cutting (GERRC) technique, pressure is offloaded via directional roof cutting, and a roadway is automatically formed due to the ground pressure and rock-breaking expansion. To improve the application of the theory and technical system of GERRC in the Karst area in Southwest China, this research studies the key technology of GERRC in a high gas outburst coal seam, based on the engineering background of the 39114 working face of the Honglin coal mine. According to the geological conditions of the 39114 working face, by means of formula calculation, UDEC numerical modeling, and on-site drilling peeping, the optimal roof-cutting parameters suitable for the 39114 working face were determined: the roof cutting height was 7 m, the roof cutting angle was 15°, and the spacing of pre-splitting blasting holes was 600 mm. Additionally, the above roof-cutting parameters have achieved good results in the engineering practices of the 39114 transportation roadway, which shows that the technology of GERRC is feasible in high gas outburst mines and achieves the goal of safe and efficient mining.

China consumes more than 3.6 billion tons of coal every year. In the meanwhile, coal accounts for over 60% of the energy consumption sector. Therefore, the sustainable development of coal mines is a problem that needed to be solved by the Chinese government. During the coal resources recovery process, the protective coal pillars between the adjacent working faces lead to a vast waste of coal resources. In order to mitigate the resource-wasting issue, a new technology of roof cutting with chain arm retaining roadway was put forward in this paper. First, the procedures of retaining roadway, roof-cutting parameters and the damage ranges of roadway surrounding rock induced by roof cutting with chain arm were analysed. Then, the working resistance of the temporary support equipment is given when using the new technology to retain the roadway. Next, the roof-cutting height, the temporary support equipment selection, working resistance of portal support and support parameters of the bolt and anchor cables were optimized based on the numerical calculation. The industrial experiment of retaining roadway by roof cutting with chain arm was carried out in a working face. The surrounding rock damage was lowered and controlled with the application of chain arm roof-cutting technology. Also, it was found that the variation range of the uniaxial compressive strength was only 5%, resulting in the roof damage range of 82 mm. The new technology has proved a potentially wide application in the coal mining industry with prosperous economic and safety improvement.

The narrow pillar mining method is widely adopted for working faces in coal mines. However, in cases of an overlying hard roof, a suspended triangle roof plate or a cantilever will be formed near the goaf. At this point, the coal pillar extrusion and serious deformation will occur in the gob-side roadway. In order to mitigate the problem, the roof-cutting technology with a chainsaw arm and its equipment have been developed. In this paper, based on the analysis of deformation and failure characteristics of 2312 roadway, which is close to the goaf of 2311 working face in Tashan Coal, the roof-cutting technology with a chainsaw arm was chosen to be applied in 2311 roadway. Then, the roof-cutting process and the load acting on the coal pillar were discussed and analysed. A numerical model was established to analyse the stress releasing effects after roof cutting. Moreover, the roof-cutting height and the support parameters of the roadway were optimized through numerical analysis and the results manifested that the roof cutting was the most effective when the roof-cutting height was 6.4 m. After roof cutting, the vertical stresses within the coal pillars were lowered by about 25.0%. Finally, the roof-cutting experiment was carried out in the 2311 roadway in Tashan Coal Mine. The on-site roof-cutting depth was 6.4 m and the roof-cutting width was 42 mm guided by the numerical analysis. To verify the stress-relieving effects, the borehole stress meters were applied to monitor the peak advancing stresses of narrow pillars at various depths. The measured results indicated that the peak advancing stresses decreased by 22.8% on average, and therefore, roof cutting and stress releasing effects were achieved.

Copyright of Journal of Central South University is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

To address the concern of intense deformation of the surrounding rock near the T-type face end formed by gob-side entry retaining, the idea of forming the L-type face end by low-pressure mining technology without pre-driving roadway is proposed, and the formation mechanism of the L-type face end and its stability and pressure behavior characteristics are studied in this paper. The results show that the roadway excavation can be canceled and that the L-type face end structure near the working face end can be formed using low-pressure mining technology without pre-driving roadway, which fundamentally eliminates the impact of advance stress on the deformation of the surrounding rock near the face end and substantially improves the stability of the surrounding rock in front of the face end. Meanwhile, on the rear side of the face end, the stress transfer path of the part roof is cut off by means of roof cutting, and a wider corner effect area is formed. Therefore, the impact of roof caving behind the working face on the deformation of surrounding rock near the L-type face end is weakened, thus significantly improving the stability of the surrounding rock. According to the engineering test, there is a certain range of the low-pressure zone of the L-type face end along the direction of the working face and the axial direction of the roadway. In the former low-pressure zone, the periodic weighting of the working face is not obvious, and the dynamic factor of the support is small; in the latter low-pressure zone, the roof-to-floor deformation of the roadway and support structure stress are both very small as well. The test results are basically consistent with the results of the theoretical analysis. The above results prove that the idea and method of forming the L-type face end using low-pressure mining technology without pre-driving roadway, thus controlling the formation of the surrounding rock near the working face end, is completely effective. [ABSTRACT FROM AUTHOR]

Based on analysis of technical advantages of gob-side entry retaining by cutting roof to release pressure, combined with geological and mining technical conditions of 19022 working face of Shiquan Coal Mine, the scheme of gob-side entry retaining by cutting roof to release pressure for Shiquan Coal Mine was proposed: high-strength anchor with single hydraulic props were selected for advanced reinforcement support of mining roadway; pre-split blasting was carried out on the roof of roadway from goaf to advanced support section to form fracture top cutting line during pressure relief; reinforcement support in the back of the working face adopted the form of sluice column + single hydraulic props lifting shed + hydraulic lifting shed. The results of mine pressure monitoring show that the average subsidence of roadway roof is 95 mm, and the average displacement of the two gangs is 225 mm, which is in line with the deformation requirements of the roadway section;the average support resistance of the roadway supports is 33 MPa, which meets the requirements of roadway support strength.

To solve the problems in blasting roof-cutting related to pressure-relief entry retaining mining, a liquid directional roof-cutting technology is proposed in this article. To verify the adaptability of liquid directional roof-cutting technology in the practice of pressure-relief entry retaining mining, a lab cutting test was performed. The effects of the four main cutting parameters (type of abrasive, pump station pressure, speed of cutting head, nozzle diameter) on cutting capacity were examined through the test, and the optimal cutting parameters thatmeet the design requirements were ultimately identified. Based on the above test parameters, field engineering test equipment was developed. The results of a hole mouth cutting test and single-hole unilateral cutting test show that the liquid directional roof-cutting technology can be used to complete field cutting work, and the cutting depth and directional function can meet the design requirements. However, some new problems were found in the field application. For example, in the process of multihole bilateral cutting, the rock mass between four holes cannot form a cut-through face. However, these problems can be addressed by increasing the cutting capacity and optimizing the seamdirection. In summary, the design idea of conducting roof directional cutting by using liquid directional cutting technology is viable, and the proposed technology is expected to replace blasting work in several engineering applications requiring pressure relief, such as impact pressure control and coal and gas outburst control. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Mine Automation is the property of Industry & Mine Automation Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The coal wall, gob-side backfill, and gangues in goaf, constitute the support system for Gob-side entry retaining (GER) in coal mines. Reasonably allocating and utilizing their bearing capacities are key scientific and technical issues for the safety and economic benefits of the GER technology. At first, a mechanical model of GER was established and a governing equation for coordinated bearing of the coal-backfill-gangue support system was derived to reveal the coordinated bearing mechanism. Then, considering the bearing characteristics of the coal wall, gob-side backfill and gangues in goaf, their quantitative design methods were proposed, respectively. Next, taking the No. 2201 haulage roadway serving the No. 7 coal seam in Jiangjiawan Mine, China, as an example, the design calculations showed that the strains of both the coal wall and gobside backfill were larger than their allowable strains and the rotational angle of the lateral main roof was larger than its allowable rotational angle. Finally, flexible-rigid composite supporting technology and roof cutting technology were designed and used. In situ investigations showed that the deformation and failure of surrounding rocks were well controlled and both the coal wall and gob-side backfill remained stable. Taking the coal wall, gob-side backfill and gangues in goaf as a whole system, this research takes full consideration of their bearing properties and provides a quantitative basis for design of the support system. [ABSTRACT FROM AUTHOR]

Roof cutting is an effective technique for controlling the deformation and failure of the surrounding rock in deep gob-side entry. The determination of the roof cutting parameters has become a popular research subject. Initially, two mechanical models are established for the non-roof-cutting and roof-cutting of gob-side entry in deep mining conditions. On this basis, the necessity and significance of roof cutting is revealed by analysing the stress and displacement of roadside prop. The Universal Distinct Element Code numerical simulation model is established to determine the key roof-cutting parameters (cutting angle and cutting height) according to the on-site situation of No. 2415 headentry of the Suncun coal mine, China. The numerical simulation results show that with the cutting angle and height increase, the vertical stress and horizontal displacement of the coal wall first increase and then decrease, as in the case of the vertical stress and displacement of roadside prop. Therefore, the optimum roof cutting parameters are determined as a cutting angle of 70° and cutting height of 8 m. Finally, a field application was performed at the No. 2415 headentry of the Suncun coal mine. In situ investigations show that after 10 m lagged the working face, the stress and displacement of roadside prop are obviously reduced with the hanging roof smoothly cut down, and they are stable at 19 MPa and 145 mm at 32 m behind the working face, respectively. This indicates that the stability of the surrounding rock was effectively controlled. This research demonstrates that the key parameters determined through a numerical simulation satisfactorily meet the production requirements and provide a reference for ensuring safe production in deep mining conditions.

In China, engineering geological disasters are frequently encountered in the underground mining sites where room and pillar method is used. This paper presents a novel method for developing the gateway tunnel without any excavation using directional tension blasting (DTB) in the mine panels. The mining-induced stress transfer will be blocked by cutting the roof stratum with a slit produced by DTB. The method has the following advantages: 1) forming the gateway tunnel without any excavation work; 2) de-stress, and 3) reducing the number of the pillars significantly. The DTB has been applied in many giant coal mining corporations in China and proved to be very helpful in 1) increase in productivity and reduction in costs dramatically, and 2) elimination of engineering geological disasters induced by the coal pillar and mining stress. [ABSTRACT FROM AUTHOR]

Based on the dynamic effect of support while roof cutting during the periodic weighting in shallow seam mining，a system mechanical model composed by upper roof，immediate roof，powered support and waste rock was established in this study. The compression quantities of the support under dynamic loading after the system instability was obtained by using catastrophic theory and rock dynamics. The support dynamic loading effect was analyzed while roof cutting，and the working resistance of support was determined. The results showed that the support capacity was related to the cycle weighting interval，the upper load and the thickness of immediate roof，also related to the stiffness ratio of immediate roof and support and the material parameters when the system was unstable. The rotation and cutting of upper roof and the unstable failure of immediate roof are main reasons for the support impact. The rationality of theoretical derivation was verified by the coal mine. [ABSTRACT FROM AUTHOR]