2. Calculation of air volume required for tunnel construction
The factors that determine the air volume required in the tunnel construction process include: the maximum number of people working in the tunnel at the same time; the maximum amount of explosives used in one blasting: the minimum wind speed specified in the tunnel: the outflow of toxic and harmful gases such as gas and carbon monoxide, and the number of internal combustion engines used in the tunnel Wait.
2.1 Calculate the air volume according to the fresh air required by the maximum number of people working in the tunnel at the same time
Q=4N (1)
where:
Q — the required air volume in the tunnel; m3/min;
4 — The minimum air volume that should be supplied per person per minute;m3/min•person
N — The maximum number of people in the tunnel at the same time (including guiding the construction); people.
2.2 Calculated according to the amount of explosives
Q=25A (2)
where:
25 — The minimum air volume required per minute to dilute the harmful gas produced by the explosion of each kilogram of explosives to below the allowable concentration within the specified time; m3/min•kg.
A — The maximum amount of explosive required for one blast, kg.
2.3 Calculated according to the minimum wind speed specified in the tunnel
Q≥Vmin•S (3)
where:
Vmin — the minimum wind speed specified in the tunnel; m/min.
S — the minimum cross-sectional area of the construction tunnel; m2.
2.4 Calculated according to the output of toxic and harmful gases (gas, carbon dioxide, etc.)
Q=100•q·k (4)
where:
100 — The coefficient obtained according to the regulations (gas, carbon dioxide gushing out of the tunnel face, carbon dioxide concentration not higher than 1%).
q — the absolute outflow of toxic and harmful gases in the tunnel, m3/min. According to the average value of the measured statistical values.
k — the unbalance coefficient of toxic and harmful gas gushing out of the tunnel. It is the ratio of the maximum gushing volume to the average gushing volume, which is obtained from actual measurement statistics. Generally between 1.5 and 2.0.
After calculating according to the above four methods, select the one with the largest Q value as the air volume value required for the construction ventilation in the tunnel, and select the ventilation equipment according to this value. In addition, the number of internal combustion machinery and equipment used in the tunnel should be considered, and the ventilation volume should be appropriately increased.
Post time: Apr-07-2022
