What Are Drill Cuttings?

Cuttings method can be used to relieve the danger of ground pressure. It is a manual method for predicting the impact ground pressure. It refers to the pre-judgment of the potential danger degree of the impact ground pressure, and is the basis for preventing the occurrence of the impact ground pressure disaster.

The cuttings method uses a small diameter (42-45mm) to drill holes. According to the amount of cuttings discharged at different depths and its changing rule, the stress concentration in the rock body is judged, and the tendency and location of the rockburst occur. During the drilling process, if the measured value of dangerous pulverized coal or the drill pipe is stuck within the specified prevention depth range, it is considered to be an impact hazard and corresponding measures should be taken to eliminate the danger. ^[1]

1. Geological factors

Mining depth: Because the stress in the coal body is almost proportional to the mining depth, the greater the mining depth, the higher the coal body stress, and the greater the elastic potential of coal body deformation and accumulation. ^[1]

Use the cuttings method to detect the impact tendency and the degree of impact danger on the working surface.

1. Drill 20 holes in the coal seam with normal pressure outside the working face, with a diameter of 42mm, a depth of 6 ~ 8m, and a spacing of 3 ~ 5m. The drilling is parallel to the inclined direction of the coal seam and the height is 1.0 ~ 1.2m from the floor. The amount of pulverized coal is then processed using the weighted average method, which is used as the standard pulverized coal amount (normal value) and a standard pulverized coal amount curve is drawn to calibrate the peak of the pulverized coal amount.

2. From the coal face of the working face to the outer roadway, the two gangs drill a hole every 3 to 5m, record the amount of coal powder per meter per hole, and then compare with the standard coal powder amount to calculate the difference. ^[1]

1. When the phenomenon of impact ground pressure occurs during the mining process, the impact tendency shall be identified in accordance with the requirements of the "Interim Regulations on the Safe Mining of Impact Ground Coal Seams", and necessary measures shall be taken in accordance with the requirements of the "Coal Safety Regulations" (2010) to prepare a special design.

2. Prevention area

The working surface is trough, the radius of the triangle area in front of the stoppage line is within 50m, and the upper lanes and dense lanes of the alleys are connected.

3. Control time and cycle

When the working face begins to mine, the prevention and control time is 20 to 100m in front of the coal wall, and the cycle is 10 days. All the pressure is released by blasting. After the pressure is released, it is reviewed by pulverized coal drilling. If pressure accumulation is found, the first Depressurization by second advanced blasting. When the working face is advanced to the 80 ~ 100m triangle door in front of the stop production line, the area of the triangle door is subjected to advanced blasting pressure relief. ^[1]

4.Advance advance prevention and control of working surface impact ground pressure by using advanced method of vibrating cannon

When using the cuttings method to measure the risk of impact ground pressure in the drilled area, the area must be pressured by advanced blasting.

(1) The lower side of the roadway within a range of 20 to 100 m in front of the coal wall of the working face is drilled every 3 to 5 m with a diameter of 42 mm and a depth of 6 to 8 m. The hole is parallel to the inclined direction of the coal seam and 1.0 away from the floor ~ 1.2m.

(2) Charge 10 ~ 15 pieces per hole, and use 2 ~ 3 detonators to detonate in parallel in a single hole. The explosive is mine ammonium nitrate explosive.

(3) Strictly seal the holes with water cannon mud and yellow mud, and the length of the hole should not be less than 2m.

(4) Strictly forward loading, reverse blasting is strictly prohibited.

(5) Strict "one shot, three inspections", "three-person chain" and sprinkler dust control system. Special personnel shall be set up at the time of blasting, and the warning line shall be no less than 150m from the blasting point. No one shall enter the cordon within 30 minutes after blasting.

(6) The firing shall be performed by a full-time licensed firing crew, with a safe firing distance of not less than 150m.

5. Coal seam high pressure water injection

In order to ensure the maximum effect of anti-impact ground pressure in the working face, high-pressure water injection must be implemented in the leading coal body in the working face to reduce the elastic properties and strength of the coal body.

(1) The water injection and pressure relief area is the coal body 0 ~ 150m in front of the coal wall of the working face, and it will move with the progress of the working face.

(2) The location of the water injection hole is under the material channel. The diameter of the drill hole should be not less than 42mm, the depth should not be less than 20m, and the spacing should be 10m. The drilling direction should be parallel to the seam bedding, and the height should be 1.1 ~ 1.2m from the floor.

(3) The initial water injection pressure is 12 MPa, and it will be maintained at 7 MPa later. The water injection time must ensure continuous water injection for 5 to 7 days, so that the water content of the coal body reaches 4% or more.

(4) Seal the hole strictly according to requirements, and it is strictly forbidden to leak water. ^[1]