Examination of Witnesses (Questions 4280
- 4299)
4280. MR TAYLOR: That is for another
time. I am sure we will be coming back to that.
4281. CHAIRMAN: Forty-one was the loudest
train, was it not?
(Mr Thornely-Taylor)
That is right, my Lord, yes.
4282. LORD YOUNG OF NORWOOD GREEN: How
did the Spitalfields residents arrive at the figure of 25? Did
they want to hear falling leaves in their houses? I am puzzled.
Where did they get that figure from?
(Mr Thornely-Taylor)
I think, my Lord, you may be right. They may have looked at one
of those scales which show what noise levels amount to and have
picked a number which meant no noise at all.
4283. MR TAYLOR: From what I have read
of the Petition, there is no explanation as to how that number
is selected.
(Mr Thornely-Taylor)
It is true to say that in that area, particularly in the Spital
Square area, the Central Line runs beneath some properties, and
following a site visit which I made I was advised to go and visit
a building in Spital Square where you can hear the Central Line,
and it is very noisy—it was about 47, I remember. That may
have given rise to the unfounded worry that there was going to
be a groundborne noise problem from Crossrail. As the layman,
understandably, they would not necessarily appreciate the enormous
improvements that have been made in track support.
4284. CHAIRMAN: Is there any validity
in a requirement that noise levels from the operating of the trains
does not exceed 25 dB? Whatever sort of dB and where we do not
know, but this is what they say.
(Mr Thornely-Taylor)
My Lord, it is quite unnecessary. It would involve a substantial
increase in cost and engineering complexity and it is not required.
4285. MR TAYLOR: If I may move on, I
was going to take the Committee to the mechanism that is proposed
for the control of groundborne noise in IPD 10, just so that we
can clarify that, because this is the first opportunity we have
had to take you to it.[45]
Starting, firstly, with paragraph 2.7 of IPD 10, it sets out the
approach to be taken to the operation of the temporary construction
railway. Can you explain, for the benefit of the Committee, Mr
Thornely-Taylor, what is proposed?
(Mr Thornely-Taylor) Yes. Behind the tunnel-boring
machine, as it advances, there will be laid a temporary railway
to enable a train to bring tunnel-mining segments up to the tunnel-boring
machine and, indeed, to bring construction workers up to the face.
This will be a long, slow train which runs nothing like as frequently
as an operational Crossrail train, but, of course, the track will
be of a temporary nature; it will not have the high standards
that we will have with the permanent track. There will be some
groundborne noise from the temporary railway, and that indeed
was the experience of the Channel Tunnel Rail Link; I think the
main thing that has been heard from that was the temporary railway
passing through, bringing tunnel lining segments and other materials
to the face. That also is subject to noise targets, as set out
in the Information Paper D10, which are the higher of the numbers
we looked at a short while ago or the noise levels which the property
concerned is already subject to from existing London Underground
tunnels.
4286. CHAIRMAN: That train will not be
taking away the spoil, will it, it is going on a conveyor belt?
(Mr Thornely-Taylor)
The spoil will go by conveyor and that will be—
4287. Does the conveyor make any noise?
(Mr Thornely-Taylor) A well-maintained
conveyor is negligible from that point of view, my Lord.
4288. MR TAYLOR: If we pass down the
page we get to paragraph 2.9, which sets out the approach to be
adopted in relation to the permanent track support system and
groundborne noise during operation. Can you take the Committee
through that paragraph, please?
(Mr Thornely-Taylor)
Yes. This is the point that I briefly mentioned a moment ago,
and that is that we will not have a railway where the track is
supported by just good enough methods to get just below 40 along
the railway. The nominated undertaker will be required to design
a system-wide track support system, which means that, if it is
achieving 40 in the worst cases, or almost all the worst cases,
as I said when describing the Hanbury Street area, it does much
better in most other locations. The essential thing about this
approach is that we do not focus on purely the numbers; it is
an approach to procuring a very well-engineered railway and a
quiet-running railway through a mechanism which comes right through
the specification of track support systems that goes to the tenderers
and to implementation of that in the construction of the railway.
We know from the very successful experience of the Jubilee Line
Extension that it works as a process, apart from just the high-level
business of selecting the right numbers.
4289. LORD YOUNG OF NORWOOD GREEN: What
about the rolling stock specification?
(Mr Thornely-Taylor)
The rolling stock specification is also important, my Lord, and
particularly what is important is the maintenance of the condition
of the wheel treads of the rolling stock, because both the rail
roughness profile and the condition of the wheel treads is important
in minimising groundborne noise, and that is all part of the process
to which I refer of procuring a quiet-running railway.
4290. MR TAYLOR: On that point, if we
look at paragraph 2.10 in IPD 10, which is on the same page, you
can see that the policy is that the nominated undertaker will
put in place measures that will ensure that the track of the underground
section and the wheels of the vehicles operating are maintained
in a state which, under all reasonably foreseeable circumstances,
will lead to adequate control of groundborne noise and vibration
arising from the railway.
(Mr Thornely-Taylor)
That is right and it is very important.
4291. MR TAYLOR: If we turn over the
page to 11 we see that the nominated undertaking will ensure that
the rails of the underground sections are conditioned by grinding
or other suitable means and are appropriately maintained thereafter
as well, so the matters that Lord Young was asking about are already
addressed in the Information Paper?[46]
(Mr Thornely-Taylor) They are indeed, yes.
4292. MR TAYLOR: Just before we leave
the issue of groundborne noise there is one last matter we ought
to address for completeness' sake which is in paragraph 2.4 on
page two of the IP and that relates to the passage of the tunnel-boring
machine and the way in which that relates to the noise criteria,
that is set at table 1.[47]
Can you explain the position, please?
(Mr Thornely-Taylor) Yes. The tunnel-boring
machine makes a noise as it excavates the tunnel under houses
and that will be clearly audible and some people may be briefly
disturbed by it. It is of relatively short duration. The tunnel-boring
machine advances at a reasonably fast rate, I think about 90 metres
a week is the current assumption which means this will be heard
for a couple of weeks, of that order. Experience in the past has
been, certainly with the Jubilee Line Extension, I am not aware
of any significant disturbance because tunnelling in the London
Clay is relatively quiet. There may be some areas where the tunnel-boring
machine is working in a soil which is less easy to excavate than
London Clay, where it will be more audible, and there will be
some disturbance and there was some disturbance with the Channel
Tunnel Rail Link tunnel boring machine for a short time.
4293. LORD YOUNG OF NORWOOD GREEN: What
sort of level are we talking about?
(Mr Thornely-Taylor) The most likely level
is in the upper 40s. It has been described to me by somebody who
has heard it as if there was a washing machine running in another
room, that sort of level of noise.
4294. MR TAYLOR: Thank you. If we can
turn away from groundborne noise—
4295. CHAIRMAN: Just before you do, as
the Petitioners are not here and I do not know whether they are
going to come, I want to ask you one point that has been raised
in two of the Petitions. There is a vertical deviation allowed
under the Bill which would enable the tunnels to be bored nearer
the surface. What, if any, difference would that make to the level
of groundborne vibration noise? Obviously it depends how much
the deviation is used but can you give us an indication of how
it works?
(Mr Thornely-Taylor) Yes, my Lord. I think
I am right in saying for most locations three metres is the maximum
deviation vertically.
4296. MR TAYLOR: Yes.
(Mr Thornely-Taylor) It is only of significant
interest where there are buildings with piled foundations because
the toes of the piles are possibly much closer to the tunnel crown
than the foundations of an older building without piled foundations
and the change takes the tunnel relatively closer to the pile
toes than it would to the surface. Based on comparative modelling
work that I have done on buildings, in those circumstances, the
most that I have found in the case of a building on piled foundations
very close to the tunnel is a change of about 3 or 4 dB on the
LAmax,S scale as a result of moving the tunnel to the absolute
maximum that is allowable under limits of the deviation in the
Bill.
4297. CHAIRMAN: And it is transferred
through the piles?
(Mr Thornely-Taylor) That is only in the
case of a building with piled foundations. It does not apply here
in this location. None of the Petitioners, as far as I am aware,
occupies a building of piled foundations, but there are one or
two locations where that does arise and that is the order of magnitude
of a potential change in alignment right to the limit of limits
of deviation. For practical reasons there are very few locations
where that could be achieved because in many cases stations are
fixed now in their position and you cannot change the tunnel alignment
very much and tie into the stations so it is most unlikely that
the whole of that limit of deviation would ever be used up.
4298. If it is not a pileborne structure, and
they go up to the maximum challenge of limits of deviation—
(Mr Thornely-Taylor) Less than 1 dB.
4299. --- on an ordinary house, what effect
would that have?
(Mr Thornely-Taylor) The effect would
be less than 1 dB, my Lord.
45 Crossrail Information Paper D10-Groundborne Noise
and Vibration, http://billdocuments.crossrail.co.uk
(LINEWD-IPD10-004) Back
46
Crossrail Information Paper D10-Groundborne Noise and Vibration,
http://billdocuments.crossrail.co.uk
(LINEWD-IPD10-005) Back
47
Crossrail Information Paper D10-Groundborne Noise and Vibration,
Table 1 Construction and Operation of groundborne noise criteria,
http://billdocuments.crossrail.co.uk
(LINEWD-IPD10-003) Back
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