Abstract
The application of roof-cutting and pressure-relief gob-side entry retention plays a critical role in controlling the stability of the surrounding rock at the entry, easing continuity tension and improving resource recovery ratio. The excavation of the 360,803 airway in Xinji No. 1 Mine is affected by intense mining of the 360,805 working face. Hence, to address the stability problem of surrounding rock in the 360,803 airway, rock mass blast weakening theory was used in this study to analyze the blasting stress of columnar charged rock mass and obtain the radiuses of crushed, fractured, and vibration zones under uncoupled charging conditions. The reasonable array pitch, length, and dip angle of boreholes were determined according to the pressure-relief range of the blasting fracture. The migration laws of roof strata were explored based on a mechanical model of overlying roof strata structure on the working face. Subsequently, the horizon, breaking span, and caving sequence of hard roof strata were obtained to determine the roof-cutting height of this entry. On the basis of the theory of key stratum, the number of sequences at the roof caving limit stratum and hanging roof length in the goaf were calculated, the analytical solution to critical coal pillar width was acquired, the evaluation indexes for the stability of entry-protecting coal pillars were determined, and the engineering requirements for the 25 m entry-protecting coal pillars in the 360,803 airway were met. Moreover, various indexes such as roof separation fracture, displacement of surrounding rock, and loose circle of surrounding rock in the gob-side entry were analyzed. The stability and cementation status of surrounding rock in the 360,803 airway were evaluated, and tunneling safety was ensured.
Highlights
Nowadays, the exploitation of coal resources is continuously extending from the shallow part to the deep part of the Earth’s crust
The #8 coal seam was mined on the 360,805 working face through longwall mining on the strike, with a dip angle ranging from 2◦ to 19◦ and on the strike, with a dip angle ranging from 2° to 19° and thickness of 1.12–4.75 m
Where k is the serial number of the hard rock stratum in the roof and floor; kr represents the total number of hard roof strata within the elliptic stress arch; Yk, Yk+1, and Ykr denote the numbers of sequences of the k(th), k + 1(th), and top hard rock strata, respectively; and
Summary
The exploitation of coal resources is continuously extending from the shallow part to the deep part of the Earth’s crust. Wang et al [10] constructed different rock strata by using similar materials such as gypsum powder, fine river sand, and barite powder, where six excavation steps along the coal seam strike were designed according to different entry retention scales They studied the caving laws of overlying strata and the deformation characteristics of surrounding rock in the retained entry through visible light imaging, high-precision digital speckle imaging, and field artificial sketching. Hua et al [13] conducted a 3D similar simulation test of roof-cutting pressure-relief gob-side entry retention and obtained the caving characteristics of overlying rock strata in the strike and dip directions and their migration laws. Through theoretical analysis of mining pressure, FLAC3D numerical simulation, and field measurement of entry deformation, Zhang et al [16] studied the roof-cutting pressure-relief gob-side entry retention mechanism of small coal pillars with a large mining height (6 m) and surrounding rock control in Fusheng Coal Mine of the Shanxi Lu’an. Ence for studying the stability of surrounding rock in entries under similar conditions
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