During the construction of semi-coal-rock tunnels, since the tunnel surrounding rock is composed of alternating coal seams and rock strata, there are characteristics such as poor stability of the coal-rock interface, high difficulty in roof management, and prominent risks of gas (if the coal seam contains gas) and water hazards. Safety measures need to revolve around the principles of "advanced prevention, dynamic control, and full-process monitoring", covering the entire process of geological exploration, support, gas, blasting, mechanical operations, and water hazard prevention. The following is a categorized explanation of key and highly practical safety measures:

   I. Core Risk: Roof Management and Support Safety (Top Priority)

   The roof of semi-coal-rock roadways often suffers from "soft coal layers and developed rock fractures," making them prone to roof collapse and spalling accidents. This requires a closed-loop control system encompassing "detection, support, and monitoring":

   1. Advanced geological survey to clarify roof characteristics

   ① Before construction, use geological radar and advance drilling (e.g., 30-meter advance drilling) to determine roof coal and rock thickness, fracture distribution, and the location of loose layers. Pay particular attention to the bond strength of the coal-rock interface to avoid blind construction.

   ② If faults, folds, or other geological structures are encountered, the construction plan must be adjusted in advance (e.g., shortening the cycle footage and strengthening support).

   2. Targeted Support Method Selection to Ensure Timely Support

   Select a support plan based on the roof rock properties, with the core principle being "short void roof, strong support, and early closure":

   ① Stable rock formations (f ≥ 6): Support method: Anchor mesh support (Φ20-22mm anchor rods, 800mm spacing) (anchor rod anchoring force ≥ 80kN, mesh overlap 100mm and welded).

   ② Soft coal and rock formations: Support method: Anchor mesh cable + steel belt support (anchor cable length ≥ 6m (through the loose layer), steel belt covering the void roof area).

   ③ Extremely unstable roof: Support method: U-shaped steel shed + anchor mesh cable support (shed spacing ≤ 600mm, shed legs rooted in hard rock, backing plate solid).

   Strictly control the "void roof distance": Excavation cycle advance ≤ 1.5m, temporary support (such as single hydraulic shoring) completed within 30 minutes after blasting, and permanent support lag no more than 2m behind the head.

   3. Real-time monitoring of roof dynamics to provide early warning of risks

   ① Install roof delamination meters (one set every 50 m, with increased frequency within the first 20 m) and monitor delamination values daily. If rock stratum displacement exceeds 5 mm/day, construction will be immediately halted and support reinforcement implemented.

   ② Appoint dedicated "roof observers" to inspect roof cracks and signs of coal seam spalling during each shift. If any signs of roof collapse, such as falling debris, noise, or crack expansion, are detected, personnel will be immediately evacuated.

   II. Gas Safety Control (If Coal Seams Contain Gas)

   Coal seams in semi-coal-rock tunnels may release gas. Strictly prevent gas accumulation and explosion risks. Measures must comply with the requirements of the Coal Mine Safety Regulations:

   1. Strengthen Gas Detection and Prevent Exceeding Limits

   ① Install methane sensors in the headstream and return airflow (≤5m for headstream, ≤10m for return airflow) to monitor gas concentrations in real time. Alarm thresholds are: ≥1.0% (power off) and ≥1.5% (evacuate personnel).

   ② Dedicated gas inspectors conduct on-site inspections every two hours, using a multi-point inspection method (headstream, coal seam fissures, and roof dead zones). Operations exceeding gas limits are strictly prohibited.

   2. Ensure a stable ventilation system and dilute gas

   ① Use "forced ventilation" (local fan power ≥11kW) to ensure a headstream air volume ≥400 m³/min, with the air duct outlet ≤5m from the headstream, and no air leaks or dead zones.

   ② Do not arbitrarily stop ventilation. If a ventilation fan fails, immediately shut off the power supply, evacuate personnel to a fresh air flow area, and activate the backup ventilation fan.

   3. Control fire sources and prevent explosions

   ① Strictly prohibit bringing fireworks into the mine. Use explosion-proof electrical equipment (such as tunnel boring machines and lighting) at the mine site. Cables must be free of damage and exposed joints.

   ② Blasting operations must use "coal mine millisecond delay electric detonators," with a final delay time of ≤130ms to prevent the blasting flame from igniting gas.

   III. Blasting Safety (Critical Process in Semi-coal-rock Roadways)

   Blasting in semi-coal-rock roadways requires a balanced approach to rock breaking efficiency and surrounding rock protection to prevent blasting vibrations from loosening the roof or causing injuries from flying rocks:

   1. Optimize blasting parameters to minimize damage to the surrounding rock

   ① Based on the differences in coal and rock hardness (coal seams f=1-3, rock seams f=6-8), adopt differentiated charging: reduce the charge in the coal seam by 20%, and charge the rock seam normally to avoid excessive coal seam fragmentation and spalling.

   ② Maintain a cycle feed of ≤1.5m, a blasthole depth of 1.8m (over 300mm), and a blasthole spacing of 600mm in the rock seam and 800mm in the coal seam to minimize the impact of blasting vibrations on the roof.

   2. Strictly implement blasting safety procedures

   ① Before blasting, perform "three inspections" (before charging, before blasting, and after blasting) to confirm that the gas concentration is ≤1.0%.

   ② Establish a "three-level alert" (at the tunneling face, tunnel entrance, and intersection). The alert distance is: ≥100m for straight tunnels and ≥75m for curved tunnels. Personnel are strictly prohibited from entering the alert area.

   ③ After blasting, wait 15 minutes (for blast smoke to dilute). Gas inspectors must check that there are no abnormalities in the gas and roof before proceeding to the front.

   IV. Mechanical Operation Safety (Tunneling and Loading Equipment)

   Tunneling machines (EBZ series) and loaders are commonly used in semi-coal-rock tunnels. Prevent equipment failure and potential harm to personnel and equipment:

   1. Daily Equipment Maintenance and Compliance

   ① Before starting work each day, inspect the cutting head, hydraulic system, and brake system of the tunneling machine to ensure that the cutting teeth are in good condition (wear ≤5mm) and that there are no leaks in the hydraulic lines. Operations with faults are prohibited.

   ② TBM operators must be certified and cut from bottom to top, from soft to hard, to avoid direct impact of the cutting head on the rock formation (to prevent equipment overload or roof vibration).

   2. Human-machine Coordination Safety

   ① When a TBM is operating, no personnel are allowed within 5 meters of the front face. If coal and rock removal is required, the machine must be shut down and the power disconnected (by displaying a "Operation Occupied, Do Not Start" sign).

   ② When loading with a loader, the bucket must not be raised above the operator's cab to avoid collisions with support equipment. Signs stating "No Pedestrians Allowed, No Vehicles Allowed" should be posted in the tunnel to prevent mixing of people and vehicles.

   V. Water Hazard Prevention and Safety

   Semi-coal-rock tunnels may encounter coal seam fissure water and old goaf water, requiring advance detection and drainage:

   1. Conduct pre-emptive water exploration to ascertain hydrological conditions

   If a tunnel passes through a coal seam or approaches an old goaf, the principle of "exploring in case of doubt, exploring before excavation" must be adhered to. Drilling combined with geophysical exploration (such as transient electromagnetic method) should be used to determine the amount of water inflow and water pressure. The depth of the water exploration hole should be ≥ 20m, and the lead distance should be ≥ 5m.

   2. Improve the Drainage System

   ① Set up a "temporary water tank" (capacity ≥ 8 hours of water inflow) at the head, equipped with two water pumps (one for use, one for backup, with lift and flow rate matching the water inflow). The diameter of the drainage pipe should be ≥ 100mm to ensure smooth drainage.

   ② Set up drainage ditches (depth ≥ 300mm) on both sides of the tunnel to promptly drain water from the roof and sides to prevent accumulated water from softening the coal and corroding the support.

   VI. Personnel and Emergency Support (Basic Support)

   1. Personnel Safety Training and Management

   ① All construction personnel must undergo "Special Safety Training for Semi-Coal-Rock Roadways" (covering roof, gas, and blasting risks) and pass the assessment before taking up their posts. New workers must shadow a team for one month to familiarize themselves with on-site risk points.

   ② Implement the "Underground Safety Confirmation System": Before the start of each shift, the team leader will conduct a safety briefing (clarifying the risks and operational requirements for the day), and all personnel must confirm this before proceeding.

  2. Emergency Response and Drills

   ① Develop a dedicated emergency plan for "roof collapse, gas explosion, and water inrush." Emergency supplies (self-rescue devices, first aid kits, hydraulic column lifters, and drainage pumps) should be provided and stored in a dedicated chamber ≤50m from the headwaters.

   ② Conduct emergency drills (such as roof collapse escape) at least once a month to ensure personnel master the use of self-rescue devices and evacuation routes. Review and optimize the plan after the drills.

   The key to safety in semi-coal-rock tunnels lies in targeted risk management—strengthening roof support based on the "soft coal, hard rock" surrounding rock characteristics, enhancing ventilation and detection for coal seam gas, and strengthening process specifications for blasting and mechanical operations. Furthermore, through proactive detection, dynamic monitoring, and full participation, risks are controlled at the nascent stage, ensuring that the entire construction process complies with the Coal Mine Safety Regulations and site geological conditions.