Civil Engineering Reference
In-Depth Information
can be contained within a single segment length for ease of construction.
The options for positioning fans are shown in Figure 7.4.
The pushing effect of the fans does not have to be distributed evenly
along the length of the tunnel. It is, for example, possible to locate all the
fans near the portals in the cut-and-cover sections, dispensing with the
need to have fans in the immersed part of the tunnel, altogether minimizing
the height of the tunnel and, therefore, the cost. The ventilation design has
to assume that some fan power is lost in an incident—for example, the fire
could be directly below a bank of fans, quickly putting them out of action.
Small number of large jet fans
Jet fans above trac clearance
envelope
Tunnel height increased
throughout
Large number of small jet fans
Jet fans above trac clearance
envelope
Tunnel height increased at
local niches
Large number of small jet fans
Jet fans above trac clearance
envelope
Tunnel height constant throughout
Figure 7.4
Location of longitudinal ventilation jet fans—cross sections and long sections
for four options.
Small number of large jet fans
Jet fans to side of trac clearance
envelope
Tunnel width increased throughout
