Research on J2 Evolution Law and Control under the Condition of Internal Pressure Relief in Surrounding Rock of Deep Roadway
Abstract
:1. Introduction
2. Engineering Situation
2.1. Engineering Geological Conditions
2.2. Characteristics of Mine Pressure in Surrounding Rock of Test Cavern
2.3. Problems Existing in The Test Cavern after Strengthening Support and Surrounding Rock Modification Technology
3. Determination of Key Parameters of Borehole Pressure Relief Model
3.1. Numerical Calculation Model
3.2. The Second Invariant of Deviatoric Stress (J2) Is Used as The Basis for Evaluating the Effect of Pressure Relief
3.3. Evaluation Index of Borehole Pressure Relief Effect and Classification of Pressure Relief Degree
3.4. Determination of Key Borehole Parameters
3.4.1. Distribution of J2 in the Surrounding Rock of the Cavern before the Borehole
3.4.2. Determination of Borehole Depth
- (1)
- Due to the excavation of boreholes in deep coal, the surrounding rock J2 is redistributed. It can be seen from the line chart that, with the increase of borehole depth, the size and peak position of the inner peak (near the roadway rib) continue to approach the peak value of the undrilled stress. On the contrary, the size of the outer peak gradually decreases, while the peak position has a tendency to shift to a deeper position than the original peak.
- (2)
- When the borehole depth is 4 m, the peak value of the outer J2 is 56.7 MPa2, and the peak position is only 2.5 m away from the original position. There is still a high J2 annular zone around the roadway, and the range of high J2 is basically consistent with that without a borehole. Even after the borehole, the peak value of J2 in the roadway rib is higher than that without the borehole, and the high J2 peak zone has a poor transfer effect to the deep surrounding rock. This shows that the borehole depth of 4 m is ineffective for surrounding rock pressure relief.
- (3)
- When the borehole depth is 10 m, the internal J2 peak is 29.1 MPa2, and the external J2 peak is 53.7 MPa2. Compared with the cases with no borehole and with borehole depth of 4 m, there is no longer a high J2 annular zone, and the influence range of the high J2 peak zone is greatly reduced. When the depth of the borehole is 10 m, and the peak position of J2 is transferred to the deep part of the surrounding rock by 8.5 m, the peak area of J2 outside the two ribs of the roadway has been effectively transferred to the deep surrounding rock of the borehole, and the original anchoring effect of the shallow part of the roadway is protected. This realizes the effective pressure relief of the surrounding rock of the roadway.
- (4)
- When the borehole depth is 12 m, the high J2 annular zone appears again around the roadway surrounding rock. The peak value of internal J2 is 39.1 MPa2, which is only 5.4 MPa2 lower than the original J2 peak value. The peak value of external J2 is 42.7 MPa2. The two ribs of the roadway form a double peak high J2 zone. The existence of double J2 peaks in the surrounding rock of the chamber is likely to cause secondary damage to the rock mass of the roadway. The borehole depth of 12 m is not conducive to the internal pressure relief of the surrounding rock.
- (5)
- When the borehole depth is 13 m, a larger range of high J2 annular zone appears around the surrounding rock of the roadway, and the range of the annular zone is similar to that of the non-borehole. The peak value of the inner J2 is 40.9 MPa2, which is only 3.6 MPa2 lower than the original J2 peak value, and the peak value of the outer J2 is 41.7 MPa2. The two ribs of the roadway will form a double peak high J2 zone larger than the 12 m range of the borehole. Therefore, a borehole according to this parameter can easily lead to a larger range of secondary damage to the surrounding rock mass and cannot protect the shallow support system of the roadway. A borehole depth of 13 m is more unfavorable to the internal pressure relief of the surrounding rock.
3.4.3. Determination of Borehole Length
- (1)
- The adjustment of borehole length will not change the shape and value of J2 in the deep surrounding rock after borehole operation. The peak value of outer J2 increases and the effect of deep transfer to surrounding rock is obvious.
- (2)
- The change of borehole length does not cause significant changes in the peak value of internal J2, but has a certain influence on the peak value and position of external J2 as well as on the distribution range of crescent J2 peak area in the figure.
- (3)
- When the borehole length is 2 m, 3 m, 4 m, or 5 m, the peak value of external J2 is 43.6 MPa2, 44.5 MPa2, 49.0 MPa2, and 53.7 MPa2, respectively. It can be seen that the change in borehole length has a certain influence on the growth of external J2 peak value, 2 m → 3 m (2.06%), 3 m → 4 m (10.11%), 4 m → 5 m (9.59%).
- (4)
- With the increase of borehole length, the peak value of outer J2 has a tendency to transfer to the deep part of the surrounding rock. Compared with the peak position of J2 without borehole, the peak position of J2 with borehole lengths of 2 m, 3 m, 4 m, and 5 m is transferred to the deep part by 4.5 m, 5.5 m, 7 m, and 8.5 m, respectively. Compared with the change range of the J2 value, the transfer range of the J2 position is larger, 2 m → 3 m (22.22%), 3 m → 4 m (27.27%), 4 m → 5 m (21.43%).
3.4.4. Determination of Borehole Spacing
- (1)
- Through the analysis of the stress curve in Figure 13, it can be concluded that, although the borehole spacing is different, the peak value of J2 along the axial direction of the cavern always appears near the middle of the two boreholes, and with the increase of the borehole spacing, the peak value of J2 gradually increases, and the influence range of the high J2 peak zone between the pressure relief holes increases.
- (2)
- Combined with the analysis of the stress cloud diagram of Figure 14, when the borehole spacing is 5~6 m, a stress concentration occurs in the surrounding rock between adjacent boreholes. This clearly shows that the high stress is transferred to the vicinity of the borehole due to the excessive selection of the borehole spacing, which is not conducive to the release of high stress between adjacent boreholes.
- (3)
- When the borehole spacing is 2 m, 3 m, and 4 m, the maximum J2 values of the adjacent borehole space rock mass are 10.1 MPa2, 10.5 MPa2, and 12.4 MPa2, respectively. Due to the small borehole spacing, the stress concentration phenomenon no longer occurs around the borehole, thus demonstrating the realization of the pressure relief work of the high-stress transfer to the deep surrounding rock in the direction of the borehole profile. Finally, considering the construction progress and economic benefits, the borehole spacing should not be too small.
4. Engineering Application
5. Conclusions
- (1)
- By analyzing and comparing the distribution, evolution, and pressure relief effect of surrounding rock J2 under different borehole parameters, it is concluded that different borehole parameters have different effects on the pressure relief effect of a roadway, which is simply summarized as borehole depth > borehole length > borehole spacing. When the borehole depth increases from 4 m to 13 m, the peak value of J2 (near the roadway rib) gradually increases but is smaller than the peak value of J2 without the borehole, and the peak value of J2 shifts to the deep part of the surrounding rock with the increase of borehole depth. When the depth of the borehole is 10 m, the peak position of J2 is transferred to the deep part of the surrounding rock by 8.5 m, which not only protects the original anchoring effect in the shallow part of the roadway but also effectively transfers the peak zone of J2 outside the two ribs of the roadway to the deep surrounding rock of the borehole. This realizes the effective pressure relief of the surrounding rock of the roadway.
- (2)
- The J2 peak value (di) and its position relationship are related to the borehole depth. The adjustment of borehole length will not change the J2 shape, position, and numerical value within 10 m of the roadway after drilling. The peak value of outer J2 has increased, and the effect of transferring to the deep part of the surrounding rock is obvious. Therefore, the buffer compensation space can be provided for the high J2 transmission and the surrounding rock deformation by reasonably increasing the borehole length.
- (3)
- On the basis of selecting the appropriate borehole depth and borehole length, the appropriate borehole spacing can release the high stress of surrounding rock and avoid the stress concentration between holes. When the borehole spacing is greater than 5 m, due to the excessive selection of borehole spacing, the higher stress is transferred to the vicinity of the borehole, which is not conducive to the release of high stress between adjacent boreholes. When the borehole spacing is less than 4 m, the borehole spacing is small, and the stress concentration phenomenon no longer occurs around the borehole, thus realizing the pressure relief work of the high-stress transfer to the deep surrounding rock in the direction of the borehole profile. However, considering the economic factors, the borehole spacing should not be too small.
- (4)
- At present, from the perspective of on-site borehole construction progress, borehole equipment seriously restricts borehole efficiency and affects the normal operation of on-site mining work. Therefore, we need to develop more advanced and efficient borehole equipment to meet borehole needs and coordinate on-site construction progress more efficiently. In addition, due to the different borehole conditions under special geological conditions, we will continue to extend the borehole pressure relief technology to different geological conditions in the future to further improve the borehole pressure relief system.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
References
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Sd/m | di/MPa2 | di/do | K(di)-K(do)/m | de/MPa2 | K(de)/m | de/do | K(de)-K(do)/m |
---|---|---|---|---|---|---|---|
4 | 8.79 | 0.20 | −4.5 | 56.7 | 11 | 1.27 | 2.5 |
10 | 29.1 | 0.65 | −1 | 53.7 | 17 | 1.21 | 8.5 |
12 | 39.1 | 0.88 | 0 | 42.7 | 18 | 0.96 | 9.5 |
13 | 40.9 | 0.92 | 0 | 41.7 | 19 | 0.94 | 10.5 |
Cd/m | di/MPa2 | K(di)/m | K(di)-K(do)/m | de/MPa2 | de/do | ∇(de)/% | K(de)/m | K(de)K(do)/m | ∇ [K(de)-K(do)]/% |
---|---|---|---|---|---|---|---|---|---|
2 | 31.5 | 7.5 | −1 | 43.6 | 0.98 | - | 13 | 4.5 | - |
3 | 30.3 | 7.5 | −1 | 44.5 | 1.0 | 2.06 | 14 | 5.5 | 22.22 |
4 | 29.5 | 7.5 | −1 | 49.0 | 1.10 | 10.11 | 15.5 | 7 | 27.27 |
5 | 29.1 | 7.5 | −1 | 53.7 | 1.21 | 9.59 | 17 | 8.5 | 21.43 |
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Chen, D.; Wang, Z.; Jiang, Z.; Xie, S.; Li, Z.; Ye, Q.; Zhu, J. Research on J2 Evolution Law and Control under the Condition of Internal Pressure Relief in Surrounding Rock of Deep Roadway. Sustainability 2023, 15, 10226. https://doi.org/10.3390/su151310226
Chen D, Wang Z, Jiang Z, Xie S, Li Z, Ye Q, Zhu J. Research on J2 Evolution Law and Control under the Condition of Internal Pressure Relief in Surrounding Rock of Deep Roadway. Sustainability. 2023; 15(13):10226. https://doi.org/10.3390/su151310226
Chicago/Turabian StyleChen, Dongdong, Zhiqiang Wang, Zaisheng Jiang, Shengrong Xie, Zijian Li, Qiucheng Ye, and Jingkun Zhu. 2023. "Research on J2 Evolution Law and Control under the Condition of Internal Pressure Relief in Surrounding Rock of Deep Roadway" Sustainability 15, no. 13: 10226. https://doi.org/10.3390/su151310226