Ventilation of tunnels
VENTILATION OF TUNNELS (EN: tunnel ventilation; DE: Tunnelbewetterung, Luttenbewetterung; FR: ventilation des galeries, aerage des galeries; ES: ventilacion de galerias; RU: вентиляция тоннелей) is the system of the activities, which is aimed towards the maintainance of the normal atmospheric conditions within the tunnels during their operation.
Within the railway and automotive road tunnels, ventilation serves for the decreasing (to the acceptable norm) of the concentration of the harmful gases (oxides of carbon and nitrogen, acrolein, and others), elimination of the dustiness of the air, the establishment of the required temperature regime, the elimination of the possible fires, and within the harsh climatic conditions, the prevention of the ice forming. Within the short tunnels, there is acceptable the natural airing on the account of the gravitational, thermal, and wind pressures, and on the account of the piston-like action of the trains or automobiles. Within the railway tunnels with the length of more than 1 kilometre, and within the automotive road tunnels with the length of more than 0.4 kilometres, they perform the artificial ventilation of the tunnels with the air exchange according to the longitudinal, transversal, or combined systems.
In case of the longitudinal system, the air is delivered and removed throughout the entire cross section of the tunnel with the speed of at most 5-6 metres per second (the tunnels with the length of at most 1 kilometre). For the intensification of the process of the airing, they use the high-speed (30-40 metres per second) axial ventilators, which are installed along the tunnel onto the walls or ceiling with the intervals of at most 40-60 metres, and which create the secondary flow of the air (the longitudinal-stream system for the ventilation of the tunnels).
In case of the transverse system for the ventilation of the tunnels, the air is delivered into the tunnel and removed with the speed of up to 15-20 metres per second through the special channels, which are situated above or under the roadway part of the tunnel; the air arrives into the transport zone through the transverse channels, which are placed with the intervals of at most 4-6 metres throughout the length of the tunnel. This system ensures the uniform inflow and ejection of the air, and may be used within the tunnels with the length of up to 1.5-1.6 kilometres. The combined system for the ventilation of the tunnels combines within itself the peculiarities of the transverse and longitudinal systems. All the systems for the artificial ventilation of the tunnels may also be used within the tunnels with the length of 2-3 kilometres and more, in case of the existence of the intermediate ventilatory shafts. Sometimes, in case of the airing of the extended tunnels, they use as the air channel the auxiliary underground mine workings (adits, galleries), which have been penetrated in parallel with the major tunnel, and which have been connected with this tunnel using the transverse passages. They place the ventilatory installations, to the structure of which there belong the axial or centrifugal ventilators, near the portals of the tunnel, above the mine shafts, or within the underground chambers.
The control and monitoring over the work of the ventilatory installations is automatic. The construction of the artificial ventilation within the railway tunnels, and especially within the automotive road tunnels, requires the significant expenditures; these expenditures reach 10-15% and more of the total cost for the construction of the tunnel. In association with this fact, along with the improvement of the existing systems, there is promising the development of the new systems for the ventilation of the tunnels, and also the physical-chemical method for the purification of the air.
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