Search

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. [ABSTRACT FROM AUTHOR]

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]

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]

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.)