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Shaped charge blasting (SCB)—a directional fracture blasting technology—has the disadvantages of low safety, harmful gas, and dust emissions. This study proposes a new type of directional rock-breaking technology called shaped charge hydraulic blasting (SCHB) that uses water as the blasting medium instead of air. To verify the effectiveness of the new method, we performed a theoretical analysis. Twelve groups of on-site directional roof-cutting tests were carried out on SCB and SCHB for comparison in a coal mine. The results showed that, although both blasting methods achieved the goal of directional roof cutting for noncoal pillar mining, SCHB had greater blasting power and produced 8% higher crack rate than SCB for the same charge amount. SCHB required 12.5% less charge than SCB when the crack rate was basically the same. SCHB effectively reduced the concentration of CO. The maximum concentration of CO was reduced by 22–62% compared with SCB. The maximum concentration decreased parabolically with the monitoring distance. In addition, water can absorb high temperature and inhibit sparks from blasting, so SCHB can prevent gas explosions. Therefore, SCHB is an environmental, safe, and economical method of directional roof cutting, which has wide applications in mining and geotechnical engineering. [ABSTRACT FROM AUTHOR]

Noncoal pillar mining with automatic formation of a roadway is a new coal mining method that is tailored to improve the coal resource recovery rate and reduce the investment in roadway tunneling. Using this proposed method, a reuse entry is formed by roof cutting instead of tunneling. In this paper, the S1201-II working face of the Ningtiaota Coal Mine was used as a case study. The stress distribution of surrounding rock and the roof deformation characteristics of the reused entry during the mining process of the second working face were studied through FLAC3D numerical simulations combined with field measurements. The results indicate that the zone close to the reused entry led to higher stress in advance. If this stress is superimposed with the lateral pressure of the adjacent mined working face, it will be more difficult to maintain the reused entry. In the engineering case study described here, the reused entry created a stress increase zone and a severe deformation zone in the range of 0–80 m in front of the working face, and its range was approximately 37.5% larger than an ordinary entry. The stress peak in the stress increase zone increased by approximately 34.7% over that of an ordinary entry. The maximum amount of deformation within the severe deformation zone increased by 94.4% over that of an ordinary entry. To properly control the surrounding rock stress and deformation of the reused entry, a dynamic pressure bearing support in front of the working face with adaptability to the large roof deformation and high support strength is proposed here. Field application results showed that the final roof deformation with the dynamic pressure bearing support can be satisfactorily controlled within 110∼130 mm. These findings can provide a reference for researchers and field engineering technicians when engaging in the support work of reused entry. [ABSTRACT FROM AUTHOR]

• A novel discontinuous similar material for physical model experiments has been developed. • The bulking characteristics of the broken goaf roof under different roof cutting conditions have been revealed. • The protection effect of the roof cutting technology for the gob-side roadway has been obtained. • The excavation compensation effect of the bulking roof rock after failure by roof cutting has been proposed. The stability control of gob-side entry retaining (GSER) has consistently been an important topic of interest within the field of no-pillar mining. This paper presents a novel discontinuous similar material for conducting physical model experiments, in conjunction with discrete element numerical simulation, to investigate the goaf roof failure and bulking characteristics based on gob-side entry retaining by roof cutting. The results indicate that the application of roof cutting technology (RCT) can significantly expand the failure range of the goaf roof vicinity to the roof cutting line. This expansion leads to a 20% increase in the volume of broken roof rock, which in turn facilitates the formation of effective support and stress compensation for the overlying strata, and the possibility of failure and displacement in the overlying strata is reduced. RCT can decrease the length of the cantilever beam located on the gob-side roadway, which is beneficial for maintaining the stability of the roadway. This paper presents a rational approach for determining an appropriate roof cutting height and angle. The in-situ application results show that the deformation of the surrounding rock of GSER by RCT is small, indicating a high level of integrity, fully meeting the requirements of serving the production of the subsequent working face. This paper serves as a reference for future research on the stability control of gob-side roadways based on GSER approach. [ABSTRACT FROM AUTHOR]