Fig 1.
Stress state of the coal around the borehole.
σ0— Pressure of the borehole surrounding the rock, φ— Internal friction angle, r0— Initial radius of the borehole, Rb, Rp— Radius of the crushing zone and plastic zone, σr, σθ —Radial stress and tangential stress, Ⅰ—Crushing zone, Ⅱ—Plastic zone, Ⅲ—Elastic zone.
Fig 2.
The distribution schematic diagram of micro-element segments in borehole.
Fig 3.
Gas flow model around the borehole.
Fig 4.
Physical picture of drill cuttings field test in the coal mine.
Fig 5.
Evolution of the amount of drilling cuttings and the pressure of surrounding rock with the depth of borehole.
Table 1.
Table of calculation parameters.
Fig 6.
The relationship of the gas drainage borehole aperture as a function of time.
Fig 7.
Three stages of borehole collapse ratio.
Fig 8.
Three stages of a typical creep curve under stress.
Fig 9.
Curve of the negative pressure change of gas drainage borehole.
Fig 10.
Schematic diagram of collapse in drainage section of borehole.
1—The sealing device of “two sealing and one grouting”, 2—Drainage pipe.
Fig 11.
Structure principle of the FDSMP sealing device.
1—The sealing device of “two sealing and one grouting”, 2—Drainage straight pipe, 3—The collapsed coal around borehole, 4—Drainage screen mesh pipe, 5—Plastic stopper.
Fig 12.
The physical picture of FDSMP.
Fig 13.
Curve of the negative pressure loss in prevention technology.
Fig 14.
Variation curve of negative pressure loss in gas drainage borehole.
Fig 15.
The schematic diagram of the drainage borehole layout.
1—The main gas drainage pipe, 2—Drainage tandem pipe of new technology, 3—Drainage tandem pipe of traditional technology, 4—Coal seam, 5—Borehole, 6—The connecting pipe.
Fig 16.
Evolution curve of the average gas drainage concentration (left) and the gas flow (right) with drainage time.