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INTERNAL INFORMATION
Northern Extension of Northolt Tunnel SIFT Report
Northern Extension of Northolt Tunnel SIFT
Report C222-ATK-DS-REP-020-000034
Revision – P06
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representative of the maximum typical height of UK Loading Gauge rail vehicles on a
non-electrified line.
4.1.9
It is assumed that the current Ruislip railhead connection would be temporary during
construction and used for fit out of HS2 only; upon completion of the works the junction
structure can be decommissioned and the connection removed. It is therefore assumed
a permanent maintenance siding would not be provided for HS2 at this location.
4.1.10
It is assumed that an appropriate design can be provided for a traction power
connection from Ickenham Auto Transformer Feeder Station (ATFS) to HS2 at rail level
via the nearest ventilation –intervention shaft.
4.1.11
For a list of environmental assumptions please refer to C252-ETM-REP=020-000116.
4.1.12
It is assumed that cross passage spacing of 380m used in the Proposed Scheme for
passengers to move from the incident tunnel to a place of safety and intervention shafts
where rescue services can access the tunnels are at approximately 3000m centres
satisfies the fire life and safety requirements for the additional tunnel options
considered.
4.1.13
The key design criteria, included as Table 4.1, include particular requirements for the
options.
Table 4.1
Key design criteria
Description
Criterion
Line speed in Chiltern and Northolt Tunnels
320kph
Line speed in Heathrow Spur Tunnel
230kph
Free cross-sectional area in bored tunnel
56m² per bore
Minimum gradient for tunnel drainage
0.5%
Geological Conditions
Drawing No C222-ATK-GT-DPP-020-000031
The Northolt Tunnel Extension is expected to be
driven through the Seaford and Newhaven Chalk
Formations (LESE) largely and, possibly, in the deeper
stretches the Lewes Nodular Chalk (LECH).
Particular features required, subject to detailed
design
For the 2014 Edition of TSI:
Additional intervention / ventilation shafts required at
nominally 3000m centres.
For compatibility with the Fire Safety strategy of the
Proposed Scheme (which does not require a Special
Safety Investigation for tunnels over 20km) 700m long
open sections [500m plus 2No 100m long perforated
portal hoods], to limit the maximum length of any
tunnel to 20km.
4.2
Applicable Safety Standards
4.2.1
The planning for safety in tunnels has followed the recommendations of the Technical
Specification for Interoperability relating to ‘safety in railway tunnels’ in the trans-
European conventional and high-speed rail system. During the assessment period this
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Northern Extension of Northolt Tunnel SIFT Report
Northern Extension of Northolt Tunnel SIFT
Report C222-ATK-DS-REP-020-000034
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document has been re-drafted and some of the fundamental requirements have been
updated/clarified.
4.2.2
The 2014 edition requires that a tunnel should have a firefighting point for a minimum
of every 20 km and within the firefighting point there should be passenger access to a
place of safety.
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Northern Extension of Northolt Tunnel SIFT Report
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Report C222-ATK-DS-REP-020-000034
Revision – P06
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5
Constraints and Issues
5.1
Study Area
Figure 5.1 Location Plan – Extract of Drawing No C222-ATK-RT-DSK-020-011301
5.1.2
The study area extends from approximately Ch 22+800m at which point the vertical
alignment of the proposed tunnel connection meets the Northolt tunnel to Ch 34+200m
where it meets the Chiltern tunnel.
5.2
Site Constraints
5.2.1
The route of the scheme is intersected by or adjacent to the following physical elements
which, depending on the option selected, may represent a constraint to development,
although the “threat” differs between baseline surface and tunnelling options:-
Lakes formed in the abandoned gravel pits (Ch27+000m to Ch29+000m), the
depths of which are not known, but geological long sections suggest the base
of the gravels, excluding any chalk solution or erosional features, are at
approximately 30mOD;
The Grand Union Canal (Ch27+000m), the construction of which may be
critical, particularly where it runs immediately adjacent to / through the lake,
and especially the canal lining type (whether puddle clay, concrete or other)
and condition. The Canal and River Trust would be expected to advise on this,
using archive drawings and local knowledge should a tunnel be introduced
into this area;
Moorhall Road (Ch27+500m);
A footpath that follows the edge of the lakes;
Sites of Special Scientific Interest (SSSI);
The River Pinn.