Influence of Water Immersion on Coal Rocks and Failure Patterns of Underground Coal Pillars Considering Strength Reduction
Abstract
:1. Introduction
2. Experimental Tests
2.1. Basic Indicators of Coal Rock
2.2. Experimental Process
3. Results and Analyses
3.1. Changes in Natural Water Absorption Rate
3.2. Uniaxial Compressive Properties
3.3. Analysis of Damage Patterns
4. Discussion
4.1. Acoustic Emission Characteristics
4.2. Fracture Evolution
4.3. Application in Coal Pillar Failure
5. Conclusions
- (1)
- The natural water absorption rate of coal rock reaches its peak after being immersed in water for 1 day. As the immersion duration increases, the absorption rate gradually stabilizes at around 20 days, indicating the gradual saturation of the coal rock with water absorption. The saturated natural water absorption rate is 1.97%. The longitudinal wave velocity of the coal rock tends to increase after water immersion.
- (2)
- Short-term water immersion results in an improvement in the plasticity of the coal rock with only a minor softening effect, resulting in a relatively complete damage morphology and a low degree of fragmentation. Conversely, prolonged water immersion results in the significant softening of the coal rock, which causes a shift in the damage morphology from shear fracture to longitudinal fracture. A negative exponential function was used to establish the relationship between the compressive strength and peak strain of the coal rock during continuous immersion, revealing a linear correlation between the elastic modulus and immersion duration.
- (3)
- The active periods of acoustic emission in coal rocks with different water immersion durations are comparable, with the most significant stress peaks occurring near the highest intensity. With increasing immersion durations, the cumulative number of acoustic events decreases, indicating the pronounced attenuation effect of water. Furthermore, the longer the immersion duration, the lower the extent of damage and the higher the level of integrity. The number of failure areas in the compressive fracture process of coal rock decreases after water immersion. The area of strain concentration forms a narrow strip in the direction of vertical lamination, and this is significantly influenced by the orientation of the primary joints within the coal.
- (4)
- The fitting curves of the compressive strength and elastic modulus under different immersion durations were obtained. The mechanical reduction relationship was applied to the failure patterns of coal pillars in underground reservoirs. The damage area of the coal pillar and the surrounding rock of the excavation area is expanded when increasing the duration of water immersion.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
References
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Time (d) | Size (mm × mm) | Mass Before Immersion (g) | Mass After Immersion (g) | Water Ratio (%) | Before Vp (km/s) | After Vp (km/s) |
---|---|---|---|---|---|---|
0 | 50.06 × 100.10 | 323.90 | 323.90 | 0 | 2.12 | / |
1 | 50.02 × 100.00 | 325.70 | 329.10 | 0.89 | 2.34 | 2.45 |
3 | 50.06 × 100.00 | 323.60 | 327.60 | 1.61 | 2.24 | 2.48 |
5 | 50.00 × 100.04 | 321.40 | 326.30 | 1.31 | 2.19 | 2.50 |
7 | 50.02 × 100.04 | 325.40 | 330.80 | 1.66 | 2.18 | 2.41 |
10 | 50.11 × 10.10 | 321.5 | 326.6 | 1.59 | 2.22 | 2.43 |
15 | 50.10 × 100.30 | 317.4 | 322.9 | 1.73 | 2.19 | 2.45 |
20 | 50.00 × 100.34 | 325 | 331.2 | 1.91 | 2.17 | 2.38 |
25 | 50.21 × 100.18 | 327.4 | 333.8 | 1.95 | 2.27 | 2.45 |
30 | 50.00 × 100.28 | 325.1 | 331.5 | 1.97 | 2.27 | 2.32 |
Rock Type | Thickness /m | Density /kg·m−3 | Elastic Modulus/GPa | Poisson’s Ratio | Cohesion /MPa | Friction/° | Tensile Strength/MPa | Compressive Strength/MPa |
---|---|---|---|---|---|---|---|---|
Aeolian sand | 20 | 1600 | 0.28 | 0.3 | 0.5 | 32 | 0.4 | 17.2 |
Sandstone | 80 | 2330 | 15.1–29.50 | 0.2–0.34 | 6–13 | 23–35 | 1.4–4.75 | 36–48 |
5−2 coal seam | 3 | 1320 | 4.89–9.30 | 0.2–0.34 | 0.5–8.8 | 12–38 | 0.25–1.36 | 13–18 |
Sandstone | 10~60 | 2380 | 15.1–29.50 | 0.2–0.34 | 6–13 | 23–35 | 1.4–4.75 | 36–48 |
Floor sandstone | 20 | 2430 | 38.0 | 0.20 | 3.2 | 38 | 2.5 | 36.5 |
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Zhu, H.; Wang, P.; Zhang, K.; Gao, Y.; Qi, Z.; Cai, M. Influence of Water Immersion on Coal Rocks and Failure Patterns of Underground Coal Pillars Considering Strength Reduction. Appl. Sci. 2025, 15, 6700. https://doi.org/10.3390/app15126700
Zhu H, Wang P, Zhang K, Gao Y, Qi Z, Cai M. Influence of Water Immersion on Coal Rocks and Failure Patterns of Underground Coal Pillars Considering Strength Reduction. Applied Sciences. 2025; 15(12):6700. https://doi.org/10.3390/app15126700
Chicago/Turabian StyleZhu, Haihua, Peitao Wang, Kewei Zhang, Yijun Gao, Zhenwu Qi, and Meifeng Cai. 2025. "Influence of Water Immersion on Coal Rocks and Failure Patterns of Underground Coal Pillars Considering Strength Reduction" Applied Sciences 15, no. 12: 6700. https://doi.org/10.3390/app15126700
APA StyleZhu, H., Wang, P., Zhang, K., Gao, Y., Qi, Z., & Cai, M. (2025). Influence of Water Immersion on Coal Rocks and Failure Patterns of Underground Coal Pillars Considering Strength Reduction. Applied Sciences, 15(12), 6700. https://doi.org/10.3390/app15126700