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Tunneling service tunnels, isolation service tunnels, and filling service tunnels—Heijinggang reports
In the underground coal mining system, the main roadway undertakes the core tasks of coal transportation and personnel passage, while the advancing side road, isolation side road, and filling side road serve as "auxiliary lifelines," each playing critical roles in development preparation, safety protection, and sustainable mining, respectively. Although all three fall under the category of side roads, they differ significantly in design principles and functional positioning—yet together, they form a vital support system for safe and efficient coal production.
1. Excavate the branch roadway
1. Definition and Core Positioning
Drifting branch roadways are auxiliary tunnels excavated during the early stages of coal mining to support the construction of main roadways—such as transportation and return air roadways. They essentially serve as the "extension arms" and "scouts" for the main roadways. Their core function is to proactively assess geological conditions and establish temporary operational passages, laying a solid foundation for the subsequent construction of main roadways and the arrangement of working faces.
2. Structural Design Features
Flexible cross-sectional dimensions: Adjusted according to the size of tunneling equipment (such as tunnel boring machines and scraper conveyors), typically featuring a cross-sectional area of 8–15㎡—smaller than the main roadway but still meeting the requirements for equipment passage and material transportation.
Support method adaptation: Anchor-net support or anchor-spray support is commonly used. For loose and soft rock strata, steel straps or anchor cables are added to ensure the stability of the surrounding rock after tunnel excavation, thereby preventing collapses.
Moving in coordination with the main alleyway: Arrange multiple secondary tunnels either parallel to the main roadway or at an angle of 30°–45°, creating a "main-secondary" interconnected tunnel network that facilitates ventilation and temporary drainage.
3. Core Features and Application Scenarios
Geological Advanced Exploration: By excavating pilot roadways, we can proactively reveal geological information such as coal seam thickness, rock fracture zones, and gas content, thereby preventing unexpected geological hazards during the construction of the main roadway.
Temporary functional support: During the tunneling phase, it can serve as a temporary return airway and a material transport lane. For instance, during the preparation of the fully mechanized mining face, supporting materials can be transported via the excavated branch tunnels directly to the main construction site.
Typical application: When developing a new mining area, first excavate 2–3 advancing crosscuts to map the coal seam distribution, then determine the orientation of the main roadway. This approach is commonly used in mining scenarios involving gently inclined coal seams (with dips ranging from 5° to 25°).
II. Isolated Branch Alley
1. Definition and Core Positioning
Isolation drifts are dedicated tunnels designed to separate hazardous areas underground in coal mines—such as gobs, high-gas zones, and areas prone to water hazards—from normal working areas. Essentially, they serve as a "safety barrier," with the primary goal of blocking pathways for disaster propagation and ensuring the safety of personnel and equipment at the working face.
2. Structural Design Features
Sealing takes priority: Sealed walls (such as concrete or inflatable types) must be installed at both ends of the tunnel, with wall leakage rates kept below 0.5 m³/(m²·h) to prevent the seepage of gas, harmful gases, or groundwater.
High support strength: Utilizing masonry arch support or a combination of U-shaped steel supports and concrete spray layers, the structure achieves a compressive strength of at least 30 MPa, effectively resisting the impact pressure generated by roof collapses in mined-out areas.
Precise positioning: Typically located between the hazardous area and the working face, at a distance of no less than 5 meters from the edge of the mined-out area. In some high-risk mines, a "double-isolation access roadway" system is implemented to provide an additional layer of protection.
3. Core Features and Application Scenarios
Disaster Isolation and Control Measures: Separate the mined-out areas from production zones to prevent gas from the mined-out areas from leaking into working faces, or to block the sudden surge of old void water (accumulated water in mined-out areas). For instance, in high-gas mines, isolating crosscuts can keep the gas concentration in the mined-out areas below 0.8%—the limit specified in the "Coal Mine Safety Regulations."
Regional functional division: In mines where multiple working faces are simultaneously mined, different mining areas are delineated by isolating crosscuts, preventing ventilation disruptions or equipment interference.
Typical application: In mines where there is a risk of old water hazards (such as coal seams in the North China Carboniferous-Permian system), isolating auxiliary roadways combined with dewatering boreholes can effectively prevent water-related accidents.
3. Filling Access Roadways
1. Definition and Core Positioning
The filling drift is a specialized drift developed alongside the "filling mining method," primarily used to transport filling materials—such as paste-like or gangue-based backfill—into mined-out areas. By supporting the roof through the backfill mass and controlling surface subsidence, it serves as a critical facility for achieving sustainable, green coal mining practices.
2. Structural Design Features
Reserved conveyance channels: The tunnels must be equipped with filling pipelines (wear-resistant steel pipes with diameters of 150–200 mm), and some branch tunnels will feature chutes to accommodate gravity-fed, self-flowing filling requirements.
Strong load-bearing capacity: The support structure must withstand lateral pressure before the filling material solidifies (typically 0.3–0.5 MPa), often utilizing reinforced concrete supports or high-strength anchor rod systems.
Grade Adaptation for Backfilling: Adjust the slope according to the backfilling method. For paste backfilling in crosscuts, the slope should generally not exceed 5°, ensuring that the backfill material is evenly delivered to the mined-out area.
3. Core Features and Application Scenarios
Control of Roof and Subsidence: By delivering backfill materials into the mined-out areas via filling drifts, the backfill material effectively supports the roof strata, ensuring that surface subsidence is kept within 300 mm—thus meeting the requirements for "three-under" mining operations: under buildings, railways, and water bodies.
Resource Recycling: Utilizing coal mine gob (mining waste) by backfilling it into mined-out areas via supporting roadways, thereby reducing the land occupation and pollution caused by surface gob mountains.
