Examination of Witnesses (Questions 6540
- 6559)
6540. Well, the Committee has got the numbers,
so I will not take time repeating them.
(Mr Griffiths) And the first floor development
IT is 47.8.
6541. The point I am going to put to you is
that, on the basis of the attenuation that is achievable using
mitigation, it is likely that a significant impact from airborne
noise from construction can be avoided within this property?
(Mr Griffiths) I am afraid I do not accept
that. I think that the reality is that when you actually look
at PPG24 and look at what you get in practice, a large area of
glazing, and you saw that on the slide, you will practically get
about 34/35, and indeed Crossrail's own figures in their Scoping
Report talk about 34 as being a reasonable standard.
6542. Can we turn then to vibration, to your
slide 17 please.[59]
There you are quoting from the specialist technical report on
noise and vibration?
(Mr Griffiths) Yes, I am.
6543. I think the passage that you are quoting
from is in volume 4 at paragraph 2.3.11, which is at page 70.[60]
If we look at that, we can see that you have actually quoted partially
from the paragraph, Mr Griffiths, because it begins: "Vibration
levels due to the use of the hydraulic breaker have been predicted
at the foundations of unattached buildings for the worst-case
situation, but the breaker works at ground level at the boundary
of the site closest to each receptor", and then it goes on
to produce the figures you have used.
(Mr Griffiths) Yes.
6544. So the figures represent the use of a
hydraulic breaker, but where the breaker is operating at ground
level at the boundary of the site closest to the receptor?
(Mr Griffiths) Yes.
6545. So these figures do not relate to oscillatory
bored piling, do they?
(Mr Griffiths) They relate to the hydraulic
breaking, yes, absolutely.
6546. It is right to say, is it not, in relation
to bored piling that that is a low-vibration technique?
(Mr Griffiths) Yes, it is.
6547. You would accept, would you not, that
the use of that technique is not going to give rise to any significant
vibration effect upon the Petitioner's premises?
(Mr Griffiths) Well, my concern, as I stated
during evidence, is that there are 6 or 7 metres of gravel which
it has to get through and one tends to have to shake the casing
in for that, otherwise everything just falls in, and there could
well be some levels of vibration. I would not expect them to be
anywhere near the 7, but they certainly could well be around the
1 millimetre or so because, looking at the piling plan, the piling
is coming somewhere between 2 to 3 metres, maybe 4 metres, from
the building.
6548. It is possible to programme that sort
of work out of office hours, is it not?
(Mr Griffiths) It could well be.
6549. In relation to the hydraulic breaker,
have you seen the correspondence from Crossrail, explaining that
the maximum use of that is likely to be two to three weeks?
(Mr Griffiths) I did see a letter, but I thought
it was saying more like six weeks, but again it was early days,
I think, when we had the meeting at Stage C on a RIBA contract.
6550. I will get Mr Thornely-Taylor to explain
that.
(Mr Griffiths) Thank you.
6551. So far as the use of a hydraulic breaker
is concerned, there are alternative methods of breaking, are there
not, the use of a cruncher, for example?
(Mr Griffiths) You could use that, yes.
6552. And that would not be as noisy, would
it, or as vibratory?
(Mr Griffiths) I would have to check that.
It probably would not be.
6553. There is also the possibility, is there
not, of detaching continuity between buildings? We can see that
from the page in front of us at 2.3.12 where you can use diamond
sawing, for example, to alter the structure of continuity between
buildings so as to mitigate vibration?[61]
(Mr Griffiths) You can do that,
but, remember, the vibration will still come around in the ground.
These vibration levels are opposite Hayne Street which is not
directly attached anyway.
6554. The figures at 2.3.11 are figures produced,
are they not, without taking into account that sort of mitigation?
They are pre-mitigation figures, are they not?
(Mr Griffiths) Yes, I am aware they are.
6555. So far as the undertakings are concerned,
I would just like to draw the Committee's attention and your attention
to what is proposed in relation to this particular Petitioner
and noise vibration. It is section 4, `Noise and Vibration'.[62]
Here we have the undertaking which is being proposed. At 4.1 there
is a commitment "to carry out the works in a manner which
will mitigate the emission of noise as far as reasonably practicable".
In fact there is another undertaking which has been provided which
is the same thing in relation to vibration.
(Mr Griffiths) Absolutely, yes.
6556. Then we see at 4.2, "The Promoter
will prepare a mitigation package in respect of noise generated
and will assign appropriate noise limits in relation to the property
and in identifying such limits factors to be considered will include
our commitment to the following . . . " and then we see the
criteria set out, yes?
(Mr Griffiths) Yes, we see a number of factors
there.
6557. And again a similar approach is adopted
in relation to vibration?
(Mr Griffiths) Absolutely, yes.
6558. It is sensible, is it not, to put off
the identification of the noise limit to take into account, for
example, change in the usage of rooms in the building in the future?
(Mr Griffiths) Just as there is for noise,
one would expect noise and vibration standards to be applied at
this stage so that in my client's particular case we would be
able to have some comfort to say that we will be achieving these
values, just as we have 35 or 40dB(A), but that does not seem
to be the case. What I am hearing, and what my client has been
concerned about, all the time is, "There is a possibility
we can do this". It says here that they will assign appropriate
noise and vibration standards. It leaves an element of risk to
my client in terms of noise and vibration.
6559. In the context of the commitment to mitigate
the emission of noise and vibration as far as reasonably practicable,
yes?
(Mr Griffiths) Yes.
59 Committee Ref: A75, Crossrail Vibration Predictions
(LONLB-505-063). Back
60
Crossrail Environmental Statement Technical Report, Assessment
of Noise and Vibration Impacts, Volume 4 of 8, Central Section,
Noise & Vibration, para 2.311, http://billdocuments.crossrail.co.uk
(LINEWD-STR112-074). Back
61
Crossrail Environmental Statement Technical Report, Assessment
of Noise and Vibration Impacts, Volume 4 of 8, Central Section,
Noise & Vibration, para 2.312, http://billdocuments.crossrail.co.uk
(LINEWD-STR112-074). Back
62
Crossrail Ref: P73, Method Statement and Programme, Para 4 Noise
& Vibration (LONLB-504-003). Back
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