Henan Coal Chemical Industry Group Hebi Coal Zhongtai Mining Co., Ltd. is a mine whose production capacity has reached 1.5 million tons after two expansions and reconstructions. Working Face 31021 is located in the No. 1 Mining District of the third level of the mine. The open-off cut is designed to be 150 m long, and the upper gateway is designed to be 560 m long, both laid out along the coal seam roof. To adapt to high yield and high efficiency, Zhongtai Company uses FRP bolt support in the open-off cut and on the mining side of the open-off cut at Working Face 31021.

 

1.1 Coal seam occurrence conditions

 

The 31021 open-off cut and upper gateway are driven in No. 2-1 coal seam of the Shanxi Formation. This coal seam is the main mineable coal seam of the mine, with large and stable thickness, and its stability is Class I.

 

Attitude of the coal seam in the 31021 open-off cut and upper gateway: strike NW323°～345°, dip direction NE53°～75°, dip angle 11°～17°. According to the coal thickness exposed in the lower section of the 31021 upper gateway, the average coal thickness of the 31021 open-off cut and intermediate open-off cut is 8 m, and the coal seam structure is 5.9 (0.3) 2.1 m. The coal seam structure is relatively complex, containing 2～3 layers of dirt bands. Among them, a dirt band of about 0.3 m in the lower part of the coal seam is relatively stable, 2.1 m above the coal floor.

 

The coal quality grade of the 31021 open-off cut and upper gateway is lean coal, dominated by bright coal, with vitreous luster, easily broken, and hardness 0.8～1.5. Average ash content 14.25%, volatile matter 14.27%, average moisture 1.4%. Plastic layer thickness K=8～29.5 mm, Y=0～5.5 mm, total sulfur content ≤0.3%, average true relative density 1.4 T/m3, calorific value 29.2 MJ/KJ. Surface elevation +205.2 m～+218.8 m, No. 2-1 coal floor elevation -430 m～-470 m, burial depth 575 m～710.5 m.

 

1.2 Surrounding rock and characteristics

 

False roof: black mudstone, bedding planes containing abundant plant stem fossils and muscovite stars, falls as mining proceeds, average thickness 0.3 m～0.5 m.

 

Immediate roof: black sandy mudstone, bedding planes containing abundant plant stem fossils and muscovite fragments. Thickness 5 m, Protodyakonov hardness coefficient f=6.37.

 

Main roof: gray medium-grained sandstone, mineral composition dominated by quartz, followed by dark black minerals, with oblique bedding, calcareous cementation, average thickness 10 m, Protodyakonov hardness coefficient f=10.5.

 

Immediate floor: gray-black sandy mudstone, sand content gradually increasing from top to bottom, average thickness 7 m.

 

 

2.1 Mine support conditions

 

At present, the coal roadway driving support of Hebi Coal Zhongtai Mining Co., Ltd. consists of U-shaped steel arches, I-beam arches, and bolt-mesh support. The roof roadway support is bolt-mesh support using metal resin bolts, with specifications: roadway width × height = 3.8 m × 2.4 m, bolt specification: L2 m, Φ20 mm metal resin bolt. Resin bolts are heavy and inconvenient to transport.

 

2.2 Overview of FRP bolt use

 

FRP bolt support technology has been widely applied in coal mine support. Due to the promotion of FRP bolt support technology and its own advantages, it has become the main support method for roadway support at present. Used in combination with anchor cables, etc., it has formed various support methods. FRP bolt support technology changes the mechanical state of the surrounding rock itself by anchoring bolts into the surrounding rock (coal), forming an integral and stable rock (coal) zone around the roadway, and utilizing the joint action of the bolt and surrounding rock (coal) to achieve the purpose of maintaining roadway stability. It is an active support method of positive defense.

 

2.3 Application of FRP bolts

 

FRP bolts are light in weight and simple in construction technology, and can improve single advance of driving. Replacing metal resin bolts with FRP bolts in coal roadways improves the stable effect on roadway support pressure and the single advance level of coal roadways, reduces the support cost of coal roadways, and lightens the labor intensity of workers. Using FRP bolt support on the mining side of the upper gateway and the mining side of the open-off cut allows the shearer to directly cut through the coal body supported by FRP bolts during face extraction, thereby improving extraction efficiency, ensuring mine succession, and achieving safe and efficient production with good economic and social benefits.

 

2.4 Support conditions of the open-off cut and upper gateway Support conditions of the 3102 open-off cut

 

Support conditions of the 3102 upper gateway

 

　3 Construction technology

 

Process flow:

 

Shift handover safety inspection → extend center and side lines → position and drill holes → charge and blast → work arch by arch (construction sequence for each arch: scaling and roof sounding, move advance support, install beam to protect roof → coal removal → erect props and set arch → coal removal, backfill sides and roof) → install supplementary bolts → lay trough → clean up and acceptance.

 

 

4.1 The following regulations shall be followed when drilling bolt holes:

 

1. Before drilling, scale and sound the roof (coal seam at the face) and pry off loose coal and dangerous blocks to ensure safety.

 

2. Check the roadway specification and quality according to the design and make them conform to the design requirements.

 

3. Determine bolt hole positions using the roadway center and side lines and the bolt spacing and row spacing, level the contact surface, and make marks. The spacing and row spacing errors must conform to the design standards.

 

4. Bolt holes should be arranged as perpendicular as possible to the bedding or main fissure planes, with deviation not exceeding 15°.

 

5. Use long and short drill rods for drilling to ensure that the direction of the bolt holes is in one plane.

 

6. Pre-measure the drill rod length and make marks on the drill rod to control the drilling depth.

 

7. When drilling bolt holes, workers must stand in a safe place. No one is allowed to stand in front of the drilling machine to prevent injury from broken rods.

 

4.2 Precautions before using the pneumatic drill

 

1. Operators must check whether all parts and fasteners are loose or falling off, whether the main shaft rotates flexibly, and whether the air pipe connection is reliable. Use only after problems are handled.

 

2. Each pneumatic drill should run idle for 3～5 min before use to check whether the mechanical parts have abnormal noise. It can be used only when the main shaft rotation direction is consistent with the arrow direction on the reducer.

 

3. Operators of the pneumatic drill must button and tighten cuffs to prevent the drill rod from entangling clothing.

 

4.3 Pneumatic drill operation sequence

 

1. If abnormal noise is heard during operation, stop drilling immediately, find the cause, and eliminate it.

 

2. During pneumatic drill operation, when the drill is stuck, stop advancing, release the operating handle, pull the drill rod back slightly, and then continue operation.

 

3. After use, place it properly in a place not easily accessible to dust to prevent blockage by debris. Carry out maintenance.

 

4.4 Bolt installation

 

1. Before installation, must check whether the roadway specification, bolt hole orientation, hole spacing, row spacing, and bolt components meet requirements.

 

2. Before installation, check the depth and straightness of the hole. The hole depth should be 30～50 mm less than the bolt length.

 

3. Before installation, the coal dust in the bolt hole should be cleaned out with a hole cleaner.

 

4. Before installation, check whether the model, color, and hand feel of the anchoring agent are soft. If there is hardening, caking, cracking, deterioration, or other abnormal phenomena, it is strictly prohibited to use.

 

5. During installation, first screw the coupling onto the thread at the tail of the rod, measure the hole depth with the rod and mark it, then slowly send the anchoring agent to the bottom of the hole with the rod, then start the mixer, rotate counterclockwise, push slowly and stir vigorously, and gradually send the rod to the bottom of the hole. The stirring time is 30 seconds for Z type and 20 seconds for K type. Do not start the mixer before the anchoring agent is sent to the bottom of the hole, to prevent the anchoring agent from concentrating not at the bottom of the hole and losing anchoring force.

 

6. After stirring, immediately wedge the rod firmly at the hole mouth to prevent displacement of the rod during curing and ensure a good bonding effect between the bolt and the hole wall after curing.

 

7. Time for installing the bearing plate: 15 minutes after stirring (if temperature changes, the bearing plate installation time can be determined according to specific site conditions). The bearing plate must be tightly against the rock surface, and the fastening screw must be tightened to strictly prevent loosening. The exposed length of the threaded part at the tail of the rod shall not exceed 50 mm.

 

8. Where the roadway roof is relatively high, before installing resin bolts, sturdy scaffolding must be erected, and the face conveyor is strictly prohibited from running.

 

9. During installation and handling, strictly prevent the curing agent (white) in the anchoring agent from contacting and damaging the eyes. If contact occurs accidentally, rinse immediately with clean water to prevent corrosion and damage to the eyes.

 

10. Damaged anchoring cartridges should be handled promptly and transported to the surface waste rock pile in gangue cars.

 

11. Anchoring agents must be transported in boxes. During transport, they must be handled gently, the boxes must be upright and stacked neatly. Collision, throwing, and squeezing are strictly prohibited to prevent the anchoring agent from cracking and becoming ineffective.

 

 

Due to the advantages of light weight and convenient transportation of FRP bolts, the use of FRP bolt support in the upper gateway and open-off cut of Working Face 31021 of Hebi Coal Zhongtai Company has further improved the driving efficiency of coal roadways, increasing the single advance of coal roadway driving at Hebi Coal Zhongtai Company by 10 m/month. Mastering the FRP bolt support technology for coal roadways and the roof management technology for roadways supported by FRP bolts, summarizing the technical management and site management during construction under special environments such as softened coal quality, increased roadway pressure, and crossing geological structure zones encountered in the construction of FRP bolt support under the geological conditions of Hebi Coal Zhongtai Company, lays the foundation for further promotion of FRP bolt support technology in Hebi Coal Zhongtai Company, and gradually realizes the full adoption of FRP bolt support technology in coal roadways of Hebi Coal Zhongtai Company.