The ventilation method used in underground tunnels is crucial for ensuring air quality, safety, and comfort for personnel inside the tunnel. Below is a detailed introduction to the ventilation systems employed in underground tunnels:

1. Classification of Ventilation Methods

The ventilation methods for underground tunnels are primarily divided into two types: natural ventilation and mechanical ventilation.

Natural ventilation: This method uses the atmospheric pressure difference between the inside and outside of the tunnel to facilitate airflow. While it eliminates the need for mechanical equipment, it is limited by natural conditions—such as temperature and pressure differences—and may result in an unstable ventilation effect.

Mechanical ventilation: A ventilation method that uses fans as the driving force, combined with ducts to deliver or exhaust air. This approach is more proactive and controllable, making it ideal for tunnels where stable ventilation performance is essential.

2. Specific forms of mechanical ventilation

Mechanical ventilation primarily comes in the following forms:

Pressurized ventilation: The ventilator forces fresh air directly into the excavation face via ducts, displacing the smoke generated after blasting with explosives. This mixed air is then exhausted out of the tunnel. This method is particularly suitable for shorter tunnels where rapid delivery of fresh air to the working area is essential.

Exhaust ventilation (also known as negative-pressure ventilation): The inlet of the ventilation fan's suction duct is positioned close to the working face, and the fan directly extracts the fumes from the tunnel, discharging them outside. Meanwhile, fresh air flows into the tunnel through the entrance, replenishing the area around the working face. This method is particularly suitable for scenarios where rapid removal of harmful gases from the tunnel is required.

Hybrid ventilation—combining both supply and exhaust systems simultaneously—effectively eliminates stagnant zones of blasting fumes at the working face while ensuring that these fumes are efficiently expelled through ducts. This approach leverages the advantages of both supply and exhaust ventilation, making it ideal for long-tunnel construction or scenarios requiring enhanced ventilation performance.

Parallel pilot-tunnel ventilation: In the construction of long tunnels equipped with parallel pilot tunnels, this method utilizes the pilot tunnels and cross passages as ventilation ducts to reduce the air pressure required by the ventilation fans. Additionally, localized ventilation systems are installed near the working face to enhance airflow. This approach enables more efficient use of ventilation energy and significantly improves overall ventilation efficiency.

3. The Structure of the Ventilation System

The ventilation system for underground tunnels typically consists of ventilators, air ducts, ventilation shafts, and a related control system. The ventilators serve as the power source, while the air ducts and ventilation shafts are responsible for delivering fresh air into the tunnel or exhausting harmful gases outside. Meanwhile, the control system monitors and adjusts the operation of the ventilation system, ensuring that ventilation performance is optimized.

4. Function of the Ventilation System

The primary functions of the ventilation system include supplying fresh air into the tunnel, removing harmful substances such as toxic gases, vapors, dust, and blasting fumes, as well as regulating temperature and humidity within the tunnel. These functions are crucial for maintaining high air quality inside the tunnel, ensuring the safety and health of construction workers, and enhancing overall construction efficiency.

5. Application Scenarios

The ventilation methods for underground tunnels are widely used in various types of underground projects, such as highway tunnels, railway tunnels, subway tunnels, and underground mines. Different application scenarios may require distinct ventilation approaches and equipment configurations to ensure that the ventilation performance meets actual needs. For instance, in subway tunnels—where passenger traffic is high and spaces are relatively enclosed—a more robust ventilation system is essential to maintain air quality and guarantee passenger comfort.