Study on Fracture and Seepage Evolution Law of Stope Covered by Thin Bedrock under Mining Influence
Abstract
:1. Introduction
2. Background of the Engineering
3. Numerical Modeling and Scheme
4. Fracture Evolution Law of Overlying Rock during Mining
5. Evolution Law of Seepage Field
6. Conclusions
- (1)
- Based on seepage and mechanics theory, a rock seepage-stress coupling equation with random damage elements is established. The numerical calculation model for the fracture evolution of the overlying rock in the stope under the coupled seepage-stress condition was established by using the ABAQUS secondary development program. A multi-scale numerical calculation method for the whole process analysis of rock mass destruction under seepage-stress coupling is realized.
- (2)
- The whole process of the overlying rock fracture evolution during the advancing process of the working face is reproduced. The results show that with the advancement of the working face, shear and tension compound rupture occurs in the overlying rock layer bottom-up. It gradually penetrates into the sand-water layer and forms a stable rupture zone, which ends at the bottom of the clay layer in the vertical direction and no longer develops upward. The damage height reached 54.5 m, which was consistent with the field monitoring results, indicating the accuracy of the numerical calculation results. The equivalent stress is used to quantify the failure trend of the surrounding rock during the advancing process of the working face. The equivalent stress concentration area is obviously separated at the bottom of the clay layer, while there is no obvious damage to the clay layer. This shows that the characteristics of the “soft–hard” roof layer greatly weaken the rupture degree of the roof caused by mining, protecting the integrity of the clay layer and ensuring its good water insulation.
- (3)
- The permeation law of the overlying rock of the roof during the advancement of the working face was analyzed, and the results were that: under the dual action of mining stress and pore water pressure, the bedrock aquifer ruptured in a wide range, and gradually caused water to flow to the goaf. The low pore pressure zone runs through the entire bedrock layer and ends at the bottom of the clay layer; also, the effective velocity of pore fluid shows a consistent pattern. This indicates that the clay layer has a good water barrier effect, effectively blocking the flow of shallow groundwater or surface water into the working face. This also shows that the “soft–hard” roof layer combination feature greatly buffers the impact of mining on the water isolation layer and has good water separation effect.
- (4)
- The monitoring results of on-site water inflow showed that during the mining of the working face, the main source of water inflow was the sandstone water layer of the bedrock section, and the shallow groundwater and surface water did not enter the working face in large quantities with the mining of the coal seam. The clay in the Quaternary overburden has not been damaged as a whole due to coal mining, which shows that the roof rock layer combination characteristics of “soft–hard alternate” greatly buffer the destructive effect of mining on the clay water separation layer, and that this has a good water separation effect.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
References
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Quaternary Loose Layer | Strata | Thickness (m) | Young’s Modulus (GPa) | Internal Cohesion (MPa) | Internal Frictional Angle (°) | The Proportion of Damaged Elements (%) | Tensile Strength (MPa) | Permeability (m2) |
Clay | 7.0 | 0.8 | 0.55 | 30.0 | 10 | 0.16 | 1 × 10–15 | |
Sand-water layer | 4.0 | 0.1 | 0.20 | 20.0 | 8 | 0.10 | 5 × 10–8 | |
Clay | 26.0 | 0.8 | 0.55 | 30.0 | 10 | 0.16 | 1 × 10–15 | |
Sand-water layer | 2.0 | 0.1 | 0.20 | 20.0 | 8 | 0.10 | 5 × 10–8 | |
Clay | 11.0 | 0.8 | 0.55 | 30.0 | 10 | 0.16 | 1 × 10–15 | |
Bedrock | Sand-water layer | 4.0 | 0.1 | 0.20 | 20.0 | 8 | 0.10 | 5 × 10–8 |
Mudstone | 6.0 | 12.1 | 2.30 | 20.9 | 9 | 0.40 | 1 × 10–13 | |
Sandy mudstone | 4.0 | 16.3 | 3.45 | 29.0 | 9 | 0.45 | 1 × 10–12 | |
Medium-grained sandstone | 8.0 | 35.0 | 5.20 | 30.5 | 7 | 6.50 | 1 × 10–10 | |
Mudstone | 5.0 | 16.3 | 3.45 | 29.0 | 9 | 0.45 | 1 × 10–13 | |
Fine-grained sandstone | 6.0 | 38.0 | 5.91 | 24.4 | 5 | 1.98 | 1 × 10–10 | |
Sandy mudstone | 3.0 | 16.3 | 3.45 | 29.0 | 7 | 0.45 | 1 × 10–12 | |
Medium-grained sandstone | 8.0 | 35.0 | 5.20 | 30.5 | 7 | 6.50 | 1 × 10–10 | |
Mudstone | 4.0 | 12.1 | 2.30 | 20.9 | 9 | 0.40 | 1 × 10–13 | |
Medium-grained sandstone | 4.0 | 35.0 | 5.20 | 30.5 | 7 | 6.50 | 1 × 10–10 | |
Mudstone | 6.0 | 12.1 | 2.30 | 20.9 | 9 | 0.40 | 1 × 10–13 | |
Coal | 3# Coal | 7.0 | 5.0 | 1.60 | 30.0 | 10 | 0.20 | 5 × 10–12 |
Floor strata | Medium-grained sandstone | 35.0 | 35.0 | 5.20 | 30.5 | 5 | 6.50 | 1 × 10–10 |
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Li, Z.; Wang, L.; Ding, K.; Ren, B.; Wang, S.; Jiang, C.; Pan, Z. Study on Fracture and Seepage Evolution Law of Stope Covered by Thin Bedrock under Mining Influence. Minerals 2022, 12, 375. https://doi.org/10.3390/min12030375
Li Z, Wang L, Ding K, Ren B, Wang S, Jiang C, Pan Z. Study on Fracture and Seepage Evolution Law of Stope Covered by Thin Bedrock under Mining Influence. Minerals. 2022; 12(3):375. https://doi.org/10.3390/min12030375
Chicago/Turabian StyleLi, Zhaolin, Lianguo Wang, Ke Ding, Bo Ren, Shuai Wang, Chongyang Jiang, and Zhiyuan Pan. 2022. "Study on Fracture and Seepage Evolution Law of Stope Covered by Thin Bedrock under Mining Influence" Minerals 12, no. 3: 375. https://doi.org/10.3390/min12030375