An Innovative Support Structure for Gob-Side Entry Retention in Steep Coal Seam Mining
Abstract
:1. Introduction
2. Geological and Mining Conditions at Awuzisu Coal Mine in Xinjiang, China
3. Shear Strength of Roadside Filling Body of Gob-Side Entry Retention Structure in Steep Coal Seam
3.1. Mechanical Model of Gob-Side Entry Retention Work in Steep Coal Seam
3.1.1. Supporting Force of Coal Wall
3.1.2. Supporting Force from Rubble inside Gob
3.1.3. Supporting Force from Filling Body
3.1.4. Shear Stress on Roadside Filling Body
3.2. Shear Strength of Filling Body
3.2.1. Supporting Force from Coal Wall
3.2.2. Supporting Force of Rubble inside Gob
3.2.3. Supporting Force from Filling Body
3.2.4. Thrust from Rubble inside Gob on Filling Body
3.2.5. Shear Strength of Roadside Filling Body
4. Discussion
5. Laboratory Experiment on Shear Performance of Backfill–Truss Support Structure
5.1. Experimental Materials
5.2. Experimental Schemes
5.3. Experimental Results
6. Field Application
6.1. Parameters of Backfill–Truss Support Structure
6.2. Construction Technology
- (1)
- Advance support was undertaken on the working face using two rows of single hydraulic props erected in the intake airflow roadway and return airway of the working face. These props were arranged at row and column separations of 1000 × 1000 mm2, and the advance-support distance was maintained at 25 m (Figure 15). After the supports of the roadway face-end were normally removed, three rows of single hydraulic props were established in the roadway retained in the gob to temporarily support the working face. These props were fixed at 1000 mm intervals in both the rows and columns, and the supporting width was 4000 mm.
- (2)
- After the working face was advanced by 3 m, densely arranged wooden pillars were used as substitutes for the single props in the side closest to the gob, followed by the construction of the filling frameworks. The lateral plate (2.8 m in height) was always perpendicular to the horizontal plane, while the inside plate was perpendicular to the inclined direction of the coal seam. Moreover, the distance between two plates in the floor strata was always 3.5 m (see Figure 15). To maintain the stability of the filling frameworks and roof, hydraulic props were fixed on one side of the lateral plate close to the retained roadway at intervals of 1 m along the advancing direction of the working face. To prevent cement grout from escaping by seepage, a plastic diaphragm was laid on the inner side of the filing plate.
- (3)
- After being uniformly mixed according to the proportions listed in Table 1, the filling materials were transported to the filling area through a pipeline beside the roadway to construct the roadside filling body.
- (4)
- Approximately four to five days after the filling body was first constructed, the roadside filling body was supported according to the designed parameters of the truss.
- (5)
- Steps 1 to 4 were repeated until the entire filling wall was constructed.
6.3. Application Effect
7. Conclusions
Acknowledgments
Author Contributions
Conflicts of Interest
References
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Proportions of the Paste Filling Materials (kg/t) | Stone Granularity (mm) | |||||||
---|---|---|---|---|---|---|---|---|
Water | Cement | Fly Ash | Gangue | River-Sand | Stone | Early Strength Agent | Water-Reducing Agent | |
134 | 164 | 44 | 85 | 227 | 340 | 2.8 | 3.2 | 5–10 |
Parameters | Tension (MPa) | Shear Strength (MPa) | Anchoring Force (MPa) | Elastic Modulus (GPa) | Extensibility | |
---|---|---|---|---|---|---|
Element | ||||||
Rock bolt | 200–600 | 260–600 | ≥50 | 200 | ≥16% | |
Steel strip | 350–400 | / | / | 200 | ≥16% | |
Steel wires, thin sheet steel | 600 | 400 | 80 | 210 | ≥16% |
Parameters | Borehole Diameter (mm) | Bolt Diameter (mm) | Space (mm) | Bolt Length (mm) | ||
---|---|---|---|---|---|---|
Element | Bolt B1 and Bolt B2 | Bolt B3 | ||||
Engineering prototype | 30 | 20 | 800 | 3000 | 1800 | |
Truss support structure | 3 | 2 | 80 | 300 | 180 |
Type | Width (mm) | Thickness (mm) | Length (mm) | Space (mm) | Diameter (mm) |
---|---|---|---|---|---|
Engineering steel strip | 280 | 32 | 3300 | 800 | 30 |
Thin sheet steel | 28 | 3.2 | 330 | 80 | 3 |
I:B:S | G% | β | RA% | Unit Weight (kN/m3) | USC (MPa) | Elastic Modulus (MPa) |
---|---|---|---|---|---|---|
1:0.25:0.22 | 2.5 | 25% | 5.0% | 2.80 | 3.29 | 1119.66 |
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Ning, J.; Wang, J.; Bu, T.; Hu, S.; Liu, X. An Innovative Support Structure for Gob-Side Entry Retention in Steep Coal Seam Mining. Minerals 2017, 7, 75. https://doi.org/10.3390/min7050075
Ning J, Wang J, Bu T, Hu S, Liu X. An Innovative Support Structure for Gob-Side Entry Retention in Steep Coal Seam Mining. Minerals. 2017; 7(5):75. https://doi.org/10.3390/min7050075
Chicago/Turabian StyleNing, Jianguo, Jun Wang, Tengteng Bu, Shanchao Hu, and Xuesheng Liu. 2017. "An Innovative Support Structure for Gob-Side Entry Retention in Steep Coal Seam Mining" Minerals 7, no. 5: 75. https://doi.org/10.3390/min7050075