Tunnel harmful gas monitoring systemIf there are harmful gases, high levels, and prominent hazards inside the tunnel; （1） Monitoring purpose and content: toxic and harmful gases, gas, carbon monoxide, etc. inside the tunnel; 1. Monitoring purpose; Tunnel gas detection (1) to prevent the danger of harmful gases exceeding the limit during tunnel construction; (2) Take corresponding measures based on the content and concentration of harmful gases;

Tunnel harmful gas monitoring system

（1） Training

Full time tile inspectors must receive professional technical training and obtain qualification certificates before they can take up their posts. All personnel entering the tunnel for construction must undergo gas knowledge training and pass the qualification before entering the tunnel for construction.

（2） Monitoring

The gas work area is inspected three times per shift, and a section is measured every 100 meters. Five points are measured on each section: the arch crown, the arch waist on both sides, and the foot of the walls on both sides. More points should be measured on the palm surface. Key monitoring shall be carried out on fault or coal seam sections and high gas bearing strata, increasing the density of monitoring sections. The key monitored airflow and sites include: excavation face return airflow, airflow within 20 meters near the blasting site, local collapse and roof caving, various operation vehicles and machinery near 20 meters, and local depressions at the top of the tunnel where harmful gases are prone to accumulate; Geological fracture zones should be inspected in a timely manner.

（3） Management measures

(1) The tile inspection instrument should be kept and charged by a dedicated person to ensure the accuracy of the test at all times. According to the instructions of various instruments, regularly send them to the inspection station for verification, and calibrate them every 3 days on a daily basis.

(2) Adhere to the "one shot, three inspections system", which means that inspections should be conducted before loading, before blasting, and after blasting.

(3) Each detection point should be clearly marked with a record board, and each detection should be promptly recorded in the gas log book and reported step by step on a regular basis.

Comprehensive treatment of harmful gases

At present, the comprehensive treatment of harmful gases in tunnels mainly adopts methods such as advanced detection, emission, ventilation, protection, grouting to stop gas, and airtight concrete sealing.

（1） Advanced detection and emissions

Using explosion-proof geological radar to conduct advanced detection of the excavation face up to a range of 60 meters ahead, understanding its geological structure and gas content. For the detected fractured and well connected gas bearing layers or larger air pockets, ZY-150 drilling rig is used for advanced drilling to determine harmful gases and discharge them through drilling. Prior to each excavation cycle, strengthen local drilling to detect any harmful gases escaping within a 5-meter range in front of the excavation face. exceed

The position of the pre drilled hole can be determined based on the attitude of the rock formation; Adopting the 5m advanced drilling technology avoids frequent movement of the drilling rig and does not interrupt the normal excavation of the tunnel. Advanced drilling can also serve as a cannon hole, saving costs and improving efficiency.

（2） Ventilation

Ventilation is the most effective means to reduce the concentration of harmful gases and prevent their accumulation; Ventilation can continuously supply fresh air to the cave, exhaust harmful gases, and reduce dust concentration, thereby improving the construction environment inside the cave, ensuring construction safety and human health, and increasing production efficiency.

1. Ventilation standards

According to experience and safety regulations, the ventilation rate should at least meet the following requirements:

(1) The oxygen content in the air inside the tunnel shall not be less than 20%, and it shall be ensured that each construction worker in the tunnel can obtain 4 meters of fresh air per minute.

(2) The allowable concentration of dust must be controlled below 2 mg per cubic meter of air for dust containing more than 10% free silica.

(3) The lowest wind speed inside the cave: mouth=0.25 (″ n/s).

2. Ventilation method

The tunnel section is large and requires a large amount of air flow. The technical key to ventilation during construction is to adjust the layout, match reasonably, and prevent leakage and obstruction. Adopt pressure ventilation. As the tunnel body continues to extend, different ventilation methods are adopted in stages. Pipeline compression ventilation; When the construction enters the tunnel for more than 1000 meters, two fans and two pipelines are used for forced ventilation according to the ventilation requirements to meet the construction requirements. In construction practice, it was found that due to the obstruction of the lining trolley, a large amount of smoke and dust accumulated inside the lining trolley. To solve this problem, a 28 kW explosion-proof small ventilation fan was installed at the overhead position of the lining trolley, and a 4.40 cm soft ventilation pipe (50 m) was installed to form local ventilation. Practice has proven that the effect is very good.