ALBERT

Description: The design and construction of roof cutting and blasting is a key part of the roof cutting pressure releasing gob-side entry retaining (RCPRGER) technology. In the existing research, the blasting parameters of roof cutting have been primarily determined by field tests. However, the disadvantages of field tests include a complicated process, which hinders the succession of related procedures, and an unstable roof cutting effect. Therefore, in this work, the authors attempt to use a mathematical analysis method to simplify the design process of the key parameters of roof cutting blasting. First, the mechanics process mechanism of surrounding rocks with roof cutting and pressure releasing is investigated, and the stress evolution process of the surrounding rock is divided into the following six stages: original rock stress state, excavation stress state, supporting stress state, roof cutting stress state, premining stress state, and postmining stress state. Furthermore, the relationship between roof cutting and entry retaining from the perspective of Mohr’s stress circle is discussed. Next, using four typical mines, including the Tashan, Yuanlin, Jinfeng, and Hengyuan coal mines, as examples, the existing design methods of roof cutting and blasting, geological data characteristics of each mine, distribution rule of roof cutting connectivity rate, and explosive charge structure of roof cutting blasting are summarized. Based on these results, the logic of roof cutting blasting design is obtained, the key indices affecting blasting design are determined, and the blasting design is defined as a complex fuzzy problem with multiple factors. Finally, based on the study of the above mechanics mechanism and blasting rule, a three-layer back propagation (BP) neural network, including six input units, nine hidden units, and three output units, is developed with the four typical mines as the sample space. This neural network realizes the rapid determination of the three key parameters pertaining to sealing length, blasthole spacing, and the explosive charge weight of a single hole. Through training, the calculation error is less than 0.48%, which considerably simplifies the design process of the blasting parameters. The charge structure parameters can also be determined according to this method. At present, the construction of this neural network has the shortcomings of limited sample space. This problem can be overcome by supplementing the sample size in the subsequent research and practice, which will improve the efficiency and accuracy of this design method and promote the application and development of the RCPRGER technology. The interdisciplinary research reported in this paper is an attempt that uses an intelligent algorithm to simplify the design process of roof cutting blasting in RCPRGER, and it represents not only an application development of the intelligent algorithm, but also a new step regarding the intelligent design of RCPRGER technology.

Description: In order to solve the problem of roadway deformation based on the theory of “short cantilever beam by roof cutting,” the method of “pressure relief by roof cutting in the adjacent roadway” is proposed. Through presplitting blasting the roadway hard rock layer, the stress propagation path is cut off, and the surrounding rock stress environment of the roadway is improved, to achieve the purpose of controlling the deformation of the roadway caused by stress. Through theoretical analysis, it is determined that the depth of the presplitting blasthole is 17 m, and the angle with the vertical direction is 10°. Based on in situ measurements and tests, by presplitting blasting the roof strata of the adjacent roadway, the maximal value of the working resistance of the hydraulic support in the presplitting blasting side of the working face decreased by 24.9%, and the average volumes of the maximum floor heave, the maximum roof subsidence, and the maximum ribs displacement were reduced by 50.1%, 34.9%, and 41.7%, respectively. This method completely changes the traditional thought patterns of “reinforcing support” to control roadway deformation from “strong support” to “pressure relief.” It provides a new idea for controlling the roadway deformation.

Description: Gob-side entry retaining is an environmentally friendly nonpillar mining technology with high efficiency and safety. With the continuous exploration of the gob-side entry retained by filling (GERF) with roadside supports, the GERF has enabled nonpillar mining. However, dense roadside supports or filled artificial pillars become subject to the pressure of roof pressure instead of coal pillars, which causes problems. Recently, an original innovative gob-side entry retaining technology by roof cutting and pressure relief (RCPR) was developed and extensively implemented in China’s coal production. The gob-side entry formed by different retaining methods has exhibited some differences in the strata behaviors and the results of retained roadways. Via industrial case and numerical simulation, this study explored the influence of entry retaining methods on the results of the entry retained. The results indicate that the total deformation of the surrounding rock of the GERF is larger and more severe; the convergence between the roof and floor and the entry sides displacement is 885 mm and 216 mm, respectively; the hydraulic support pressure near the retained entry is larger; and the peak value is 38.7 MPa. The deformation of the surrounding rock by RCPR is relatively small; the convergence between the roof and the floor and the entry sides displacement is 351 mm and 166 mm, respectively; the hydraulic support pressure near the retained entry is weakened to a certain extent; the peak value is 32.2 MPa; and the peak pressure is reduced by 16.8% compared with the GERF. A numerical simulation analysis reveals the following findings: RCPR changes the surrounding rock structure of a gob-side entry, optimizes the surrounding rock stress environment, and belongs to active pressure-relief entry retaining; the GERF does not adjust the surrounding rock structure of a gob-side entry and belongs to passive pressure-resistance entry retaining; and the surrounding rock of a gob-side entry is significantly affected by pressure. These two methods of gob-side entry retaining have different effects on the surrounding rock of the entry retained. This study can contribute to an exploration of the strata behaviors and the results of a retained roadway by the GERF or RCPR method.