Study on the Pressure Relief Mechanism and Engineering Application of Segmented Enlarged-Diameter Boreholes
Abstract
:1. Introduction
2. Destressing Mechanism of Segmented Enlarged-Diameter Borehole
2.1. Stress Distribution Characteristics around the Segmented Enlarged-Diameter Borehole
2.2. Determination of Segmented Enlarged-Diameter Position of Large Diameter Pressure Relief Boreholes
2.3. Mechanism of Segmented Enlarged-Diameter Borehole Destressing
3. Simulation Schemes
3.1. Numerical Model and Simulation Schemes
- (1).
- Different diameters of enlarged-diameter section
- (2).
- Different lengths of the enlarged-diameter section
- (3).
- Different borehole spaces
3.2. Effect of Diameter of the Enlarged-Diameter Section on Pressure Relief Effect and Roadway Deformation
3.3. Effect of Lengths of the Enlarged-Diameter Section on Pressure Relief and Roadway Deformation
3.4. Effect of Borehole Space on Pressure Relief Effect and Roadway Deformation
4. Field Test
4.1. Key Parameters for Segmented Enlarged-Diameter Borehole
- (1).
- Total borehole lengthReferring to the borehole pressure relief parameters of the adjacent working face of the 6307 working face, the length of the pressure relief borehole of the 6307 working face was determined to be 20 m.
- (2).
- Diameter of the unenlarged-diameter sectionAccording to the simulation results in Section 3.2, when the diameter of the hole in the unenlarged-diameter section was 90 mm, the roadway deformation was relatively small. Thus, the diameter of the borehole in unenlarged-diameter section was determined to be 90 mm.
- (3).
- Diameter of enlarged-diameter sectionAccording to the simulation results in Section 3.2, with increasing diameter of the enlarged-diameter section, the peak elastic strain energy density gradually transfered to the deep surrounding rock of the roadway. The displacement on both sides of the roadway was less affected by the enlarged diameter section. Therefore, the diameter of the enlarged-diameter section was determined to be 240 mm.
- (4).
- Length of enlarged-diameter sectionBased on the roadway support design in the 6307 working face, the length of unenlarged-diameter was calculated to be no less than 3.7 m (Equation (14)). According to the simulation results (Section 3.3), it has little influence on the support system when the position of enlarged-diameter section was 5 m away from the roadway side. The length of enlarged-diameter section in roadway of 6307 working face was determined to be 15 m.
- (5).
- Borehole spaceAccording to the simulation results in Section 3.4 (Figure 18), when the space between pressure relief boreholes was less than 1.6 m, the decrease in space will not improve the pressure relief effect. However, it will significantly increase roadway deformation. Considering the construction and safety factors, the space of pressure relief borehole was determined to be 1.6 m. Table 5 and Figure 23 present the key parameters of the segmented enlarged-diameter borehole in the 6307 working face roadway.
4.2. Pressure Relief Effect Monitoring
4.2.1. Coal Stress Monitoring
4.2.2. Roadway Deformation Monitoring
5. Conclusions
- (1).
- According to the theory of elastic-plastic mechanics, the distribution range and influencing factors of the coal pressure relief zone around the borehole are obtained. Furthermore, the minimum length of the unenlarged-diameter section of the borehole was determined.
- (2).
- The effects of diameter of the enlarged-diameter section, length of the enlarged-diameter section, and borehole space on pressure relief and roadway deformation were investigated. The larger the diameter of the enlarged-diameter section, the better the pressure relief effect. With increasing diameter of the enlarged-diameter section, the displacement on both sides of the roadway changed slightly. Increasing the length of the enlarged-diameter section can effectively reduce the energy accumulated around the boreholes and transfer the energy peak to the deep surrounding rock. However, the longer the length of the enlarged-diameter section, the larger the deformation of the surrounding rock. With decreasing borehole space, the peak energy around the boreholes decreased, and the deformation of both sides of the roadway increased significantly.
- (3).
- The key parameters of segmented enlarged-diameter pressure relief borehole were determined for 6307 working face. Field monitoring results showed that the accumulated energy can be effectively reduced using segmented enlarged-diameter pressure relief boreholes, effectively controlling the roadway deformation. Segmented enlarged-diameter pressure relief technology can effectively mitigate the problems of excessive pressure relief (the strength of the surrounding rock was reduced after pressure relief) and insufficient pressure relief (rock burst still occurred after pressure relief) as well as provide a reference for the rock burst prevention and roadway stability control.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
References
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Rock Type | Thickness /m | Density kg/m3 | Bulk Modulus/GPa | Shear Modulus/GPa | Tension Strength/MPa | Cohesion /MPa | Friction Angle /(°) |
---|---|---|---|---|---|---|---|
Medium sandstone | 4.9 | 2570 | 7.95 | 6.87 | 4.52 | 6.12 | 31 |
Siltstone | 5.4 | 2700 | 16 | 10 | 2.3 | 2.4 | 32 |
Mudstone | 2.4 | 2550 | 3 | 1.3 | 1.5 | 1.7 | 29 |
Medium sandstone | 5.4 | 2570 | 7.95 | 6.87 | 4.52 | 6.12 | 31 |
Mudstone | 4.4 | 2550 | 3 | 1.3 | 1.5 | 1.7 | 29 |
Coal | 9.4 | 1400 | 1.5 | 0.7 | 1.1 | 1.2 | 23 |
Siltstone | 3.2 | 2700 | 16 | 10 | 2.3 | 2.4 | 32 |
Fine sandstone | 10.9 | 2620 | 8.5 | 5.6 | 4.7 | 5.52 | 35 |
No. | Total Borehole Length l1/m | Length of the Enlarged-Diameter Section l2/m | Diameter of the Unenlarged-Diameter Section d1/mm | Borehole Space s1/m | Diameter of the Enlarged-Diameter Section d2/mm |
---|---|---|---|---|---|
1 | 20 | 15 | 90 | 1.6 | 90 |
2 | 20 | 15 | 90 | 1.6 | 140 |
3 | 20 | 15 | 90 | 1.6 | 190 |
4 | 20 | 15 | 90 | 1.6 | 240 |
No. | Total Borehole Length l1/m | Diameter of the Unenlarged-Diameter Section d1/mm | Diameter of the Enlarged-Diameter Section d2/mm | Borehole Space s1/m | Length of the Enlarged-Diameter Section l2/m |
---|---|---|---|---|---|
1 | 20 | 90 | 240 | 1.6 | 11 |
2 | 20 | 90 | 240 | 1.6 | 13 |
3 | 20 | 90 | 240 | 1.6 | 15 |
4 | 20 | 90 | 240 | 1.6 | 17 |
5 | 20 | 90 | 240 | 1.6 | 19 |
No. | Total Borehole Length l1/m | Length of the Enlarged-Diameter Section l2/m | Diameter of the Unenlarged-Diameter Section d1/mm | Diameter of the Enlarged-Diameter Section d2/mm | Borehole Space s1/m |
---|---|---|---|---|---|
1 | 20 | 15 | 90 | 240 | 0.8 |
2 | 20 | 15 | 90 | 240 | 1.6 |
3 | 20 | 15 | 90 | 240 | 2.4 |
4 | 20 | 15 | 90 | 240 | 3.2 |
Total Length of Borehole /m | Diameter of Enlarged-Diameter Section /mm | Diameter of Unenlarged-Diameter Section /mm | Length of Enlarged-Diameter Section /m | Borehole Space /m |
---|---|---|---|---|
20 | 240 | 90 | 15 | 1.6 |
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Gu, S.; Chen, C.; Jiang, B.; Ding, K.; Xiao, H. Study on the Pressure Relief Mechanism and Engineering Application of Segmented Enlarged-Diameter Boreholes. Sustainability 2022, 14, 5234. https://doi.org/10.3390/su14095234
Gu S, Chen C, Jiang B, Ding K, Xiao H. Study on the Pressure Relief Mechanism and Engineering Application of Segmented Enlarged-Diameter Boreholes. Sustainability. 2022; 14(9):5234. https://doi.org/10.3390/su14095234
Chicago/Turabian StyleGu, Shitan, Changpeng Chen, Bangyou Jiang, Ke Ding, and Huajian Xiao. 2022. "Study on the Pressure Relief Mechanism and Engineering Application of Segmented Enlarged-Diameter Boreholes" Sustainability 14, no. 9: 5234. https://doi.org/10.3390/su14095234