Civil Engineering Reference
In-Depth Information
Tunnel roof slab
Services gallery
Trac bore
Pedestrian escape
gallery
Decking
Emergency escape door
Pipe gallery
Tunnel base slab
Figure 7.2
Central services/escape bore.
the tunnel systems. A common arrangement is to divide the escape bore
into two or three compartments, with cable and pipework running above
and below the pedestrian escape route (Figure 7.2). This central bore can
also accommodate the step down transformers and switchgear needed for
the tunnel systems.
Combining the escape and services facilities in this way does present
some problems. The electrical systems will almost certainly require tech-
nical rooms to house transformers and similar equipment, particularly in
longer tunnels. These are likely to be near the middle of the tunnel and
will take up most, if not all, of the room in the central bore, blocking it
as an escape route. If this is the case, a risk assessment will be required
and a strategy developed, with clear signing to direct people in the right
direction.
Pedestrians must have a safe route from their vehicles to these emer-
gency exits. This should preferably be at a low level. Raised walkways,
which were often used in the past as they separated pedestrians from
the traffic and gave the pedestrian more reassurance, are not favored
now in some countries as access to them is restricted and people with
impaired mobility cannot get on to them. Even access walkways at low
level should be provided with dropped kerbs adjacent to the emergency
exits to permit wheelchair access. In the United States, raised walkways
are still used, but this is for maintenance access and not for escape.
Low-level gaps are provided in the raised walkways to give access to the
escape doors.
The escape doors are usually highlighted by the use of color on the walls
around them, with direction signs placed on the walls to give the direction
