Experimental investigation on basic law of rock directional fracturing with static expansive agent controlled by dense linear multi boreholes

Abstract

Directional rupture is one of the difficult problems in deep rock mechanics and engineering. A directional fracturing method with static expansive agent controlled by dense linear multi boreholes is proposed. A physical experiment is designed and performed to investigate the basic laws of this method. The fracture initiation and propagation process, and the mechanism of directional fracturing are analyzed. The results indicate that a directional fracture is formed along the direction of boreholes layout through directionally fracturing with static expansive agents controlled by the dense linear multi boreholes. According to the variation of strain and the distribution of associated acoustic emission (AE) events and energy, the experiment can be divided into three stages. In the first stage, the static expansive agent expand slowly with no fracturing inside the rock. In the second stage, some initial micro-fracturing occurs inside the rock. In the third stage, a wide range of fracturing occurs inside the sample. The internal micro-fracturing planes are connected to form a macro-fracture. Finally, it propagates to the surface of the sample. The directional fracturing plane presents a relatively smooth plane with little bias but much local fluctuation.

Hydraulic fracturing method for relieving stress concentration in remaining coal pillar in overlying goaf

“…(1) Using pulse hydraulic fracturing technology, [17][18][19] a dense network of cracks is formed in the hard roof directly above the coal pillar, fully crushing this area. By using directional hydraulic fracturing technology, 20,21 the hanging roof of the goaf on both sides of the coal pillar is cut off, effectively optimizing the stress above the coal pillar and reducing the source of stress.…”

“…16 The specific ideas are as follows: Using pulse hydraulic fracturing technology, 17–19 a dense network of cracks is formed in the hard roof directly above the coal pillar, fully crushing this area. By using directional hydraulic fracturing technology, 20,21 the hanging roof of the goaf on both sides of the coal pillar is cut off, effectively optimizing the stress above the coal pillar and reducing the source of stress. By using pulse hydraulic fracturing technology, 17–19 a dense network of cracks is formed within the coal pillar, fully crushing this area, reducing the stiffness of the coal pillar, and thereby reducing the bearing capacity of the coal pillar. By using pulse hydraulic fracturing technology, 17–19 a dense network of cracks is formed in the hard floor directly below the coal pillar, fully crushing this area, thereby weakening the ability to transmit stress concentration. At the same time, the fractured area formed in the coal pillar and its roof and floor using pulse hydraulic fracturing technology can absorb the dynamic pressure generated by the collapse of the roof on both sides of the coal pillar, preventing the transmission of dynamic pressure to the lower part of the coal pillar.…”