Research on the Key Technology of Gob-Side Entry Retaining by Roof Cutting for Thick and Hard Sandstone Roofs

Abstract

In order to ensure the application of gob-side entry retaining by roof cutting for thick and hard sandstone roofs, the key technology of pre-split blasting was studied. The LS-DYNA was used to analyze the blasting effect of the energy-gathering pipe. Using the methods of theoretical analysis and numerical simulation, it was determined that the optimal cutting height was 16 m and the optimal cutting angle was 15°. The effect of pressure relief by roof cutting was verified by FLAC3D. It is proposed to use deep-hole loosening blasting to solve the problem of the sandstone with a thick hard roof being difficult to collapse. A group of loose blasting holes was designed to be arranged every 20 m in the gob-side roadway. The depth of the #1 blasthole was 47 m, and the angle to the horizontal direction was 20°; the depth of the #2 blasthole was 65 m, and the angle to the horizontal direction was 15°. A field test was carried out in the 7135 ventilation roadway of Qidong Coal Mine China. The on-site peeping results showed that the blasting with the energy-gathering pipe had a good effect of directional slitting. After deep-hole loosening blasting, the thick hard sandstone roof collapsed and filled the gob in time. The monitoring curves of the hydraulic support showed that the hydraulic support resistance of the working face in the side with roof cutting was much smaller than that of the side without roof cutting, and the effect of pressure relief by roof cutting was good.

Key parameters of gob-side entry retaining by roof cutting in close-distance seam group

“…This technique cuts off the roof strata of the roadway and gob using bidirectional concentrated blasting technology. After the working face is mined, the roof strata of the gob collapses and forms a new rib [4][5][6]. Compared with traditional technology for gob-side entry retaining, this method has completely changed the core idea of replacing coal pillars with back ll and removed the need for roadside back ll.…”

Solid waste filling and roadway retaining for longwall mining by numerical investigation

“…Some scholars have analysed the technical difficulties and construction keys of the roadway retaining and solid waste filling [ [16] , [17] , [18] , [19] ]. Some scholars have analysed the deficiencies of the roadway retaining and solid waste filling technology, and put forward the formation of roadside support by filling gangue belt and grouting reinforcement of filling body [ 18 , [20] , [21] , [22] ]. Therefore, it further improves the deficiency of this technology in deep filling mining conditions [ [23] , [24] , [25] , [26] ].…”

Study on Stress Characteristics and Supporting Countermeasures of Surrounding Rock in Roadway Formed by Composite Roof Cutting in Three-soft Coal Seam

“…In contrast, the mining technology of gob-side entry retaining without coal pillars by roof cutting and pressure relief is a revolution of mining technology [6], which not only realizes the purpose of retaining no coal pillars but also blocks the stress transmission path between the gob roof and the roadway roof by roof cutting and pressure relief [7] so that the gob roof collapses itself to form a roadway by roof cutting. The stability of the surrounding rock in a roadway self-formed by roof cutting are affected by many factors, including roof and floor lithology of the working face [8], blasting-aided roof cutting parameters [9], and supporting parameters beside the roadway [10]. With the rapid development of high-strength anchor bolt supporting materials in recent years, the gob-side entry retaining technology that performs supporting by anchor bolts as the main materials has achieved a favorable application effect [11], the surrounding rock control technology of gob-side entry retaining without coal pillars has been greatly improved.…”