Examination of Witnesses (Questions 5220
- 5239)
5220. I will move on to the subject of noise.
I obviously do not want to waste time on issues which are not
in dispute, but I would like your confirmation on a number of
matters, so that the Committee are clear that the record is straight.
As far as airborne noise is concerned—and I will take this
collectively—the airborne noise attributable to ground shaft
construction and operation and the airborne noise associated with
construction and demolition works at Fareham Street, so that is
Soho Square side of the building and Dean Street side of the building—is
such that you recommend noise insulation should be provided. Is
that right?
(Mr Thornley-Taylor) Yes.
5221. That is both on the Soho Square frontage
and the Dean Street frontage.
(Mr Thornley-Taylor) Yes.
5222. We can turn from airborne noise to groundborne
noise. Do you have a copy of your report to hand with Mr Kahn's
numbering on it?
(Mr Thornley-Taylor) I have Mr Kahn's exhibit,
tab 3, yes.
5223. You deal with groundborne demolition noise
is concerned, you deal with that at 9.20.[47]
(Mr Thornley-Taylor) Yes.
5224. You say: "It is currently predicted
that ..." and then you give a prediction. Would the Committee
be right in understanding, if they go back to 3.9 and 3.10, that
some of these predictions and those particular predictions are
based on what you describe at 3.10 as "using expert judgment
and experience".[48]
(Mr Thornley-Taylor) Yes.
5225. They are not numerical calculations but
based upon your judgment. Is that right?
(Mr Thornley-Taylor) The groundborne demolition
noise assessment is based on expert judgment and experience.
5226. It is your judgment at 9.20 that the adverse
effect will not be limited to the basement film theatre but may
extend to the higher floors during the course of demolition, and
that is the one week period you spoke to in examination-in-chief,
is that right?
(Mr Thornley-Taylor) Yes.
5227. Could we go to 9.23, please: "Groundborne
noise from work in the basement of 2-4 Dean Street may also cause
intrusion in the upper floors of 3 Soho Square/7 Dean Street to
an extent that can be established by the on-site tests described
above." This is under construction rather than demolition.
Is that additional to the demolition?[49]
(Mr Thornley-Taylor) This is the
work that is necessary in the basement of 2-4 Dean Street preparatory
to grouting for the construction of the other escalator further
north than BBFC. Because that will mean breaking out the existing
concrete floors in 2-4 Dean Street, depending on the way the breaking
out is done, it is necessary to describe the potential effect
in these words. On previous Crossrail projects in the early 1990s,
we had an analogous problem in another building and did in fact
set about their floor with various forms of breaking equipment
to measure the comparative effect of different methods in terms
of received groundborne noise levels in sensitive rooms, and we
did find there is a very wide variety of effects from different
methods of cutting and breaking. I am recommending here that the
same should be done, so that we can establish that if you use
diamond sawing it does not have an effect on BBFC; if you use
a Kanga hammer it does. There are many ways of doing it and this
particular source is much more capable of mitigation than the
previous one we were considering at 9.20.
5228. The answer to my question is that it is
additional to the source mentioned at 9.20.
(Mr Thornley-Taylor) It is, yes.
5229. At the moment, it may also cause intrusion
to the upper floors. If it did, it would be in addition to the
one week period that you identified in examination-in-chief. Is
that right?
(Mr Thornley-Taylor) If it did, it would be.
I do not think it will be because of the mitigation options I
have described.
5230. Have you considered over how long a period
such disruption would occur? We know how long the work will take
place there because you have given us a period in 9.21 of three
to six months.
(Mr Thornley-Taylor) Well, my discussions with
engineers since writing this report indicate that the need to
use percussive methods is minimal. Even if it should be necessary,
the duration would be of the same kind of order.
5231. So of the undertakings or the elements
of the matters that you say you will carry out, can we add to
those matters that, when carrying out work to 2-4 Dean Street,
the sawing method which you just described will be used?
(Mr Thornley-Taylor) Well, it all goes back
to the fundamental approach to construction noise control which
I have addressed to the Committee in evidence about before, the
section 61 process, which brings about the use of the best practicable
means, and the choice of the different methods of cutting and
breaking that I have been describing most certainly fall within
that test of best practicable means. It is not really necessary
to add any further assurance or undertaking.
5232. But if undue disturbance is to be avoided,
then such methods will have to be adopted, whether you are prepared
to give a specific undertaking or not?
(Mr Thornley-Taylor) Well, the undertaking
is given generically through the approach using section 61 and
it will be necessary to use the best practicable means.
5233. Can we then move on to construction of
the escalator shaft. If we go to your 9.25, the prediction there
is that during construction of the escalator shaft, the likely
level of groundborne noise during excavation is 55dBLAmax and,
as you say, this would be clearly intrusive in the basement film
theatre over a period of six months and would exceed your criterion
and be wholly unacceptable in the basement film theatre. Is that
right?[50]
(Mr Thornley-Taylor) Yes.
5234. What we do about it we will come on to
in a moment. The construction and operation of the grout shafts
in Soho Square, if we go to 9.28, you say, "The potential
for groundborne noise during construction of the grout shafts
is of the same order as that for the grouting work in the basement
of 2-4 Dean Street", and that again gives rise to elevated
and unacceptable noise levels in the basement film theatre.[51]
Is that right?
(Mr Thornley-Taylor) Purely the
use of the breaking through of the paving surface, but the grouting
itself is a comparatively quiet operation and does not give rise
to the levels that were described for the breaking out of concrete
paving before the grout shaft is sunk or the grouting begins.
5235. During that part of the construction activity,
there will be unacceptably elevated levels of noise?
(Mr Thornley-Taylor) It will be exactly the
same as any other utility breaking the road surface outside, which
I am sure happens from time to time.
5236. As far as operational noise is concerned,
this is at 9.34, unless mitigation measures are taken, the operation
of the southern bank of escalators will lead to an `exceedence'
above the standard that you consider appropriate?[52]
(Mr Thornley-Taylor) Yes.
5237. As a result of that analysis, there is
no dispute between us that solutions must be found. Is that right?
(Mr Thornley-Taylor) That is right.
5238. As far as your suggestions are concerned,
in this report you make a number of suggestions about the sequence
of works, stopping of work and the like, but they have now all
been superseded by the suggestion of an isolation shell. Is that
right?
(Mr Thornley-Taylor) Yes. `Shell' is not quite
the word, it is a floating foundation for the escalator.
5239. I think I called it an `isolation chamber'.
(Mr Thornley-Taylor) It does not enclose the
escalator, it is a floating foundation for the escalator truss.
47 Committee Ref: A59, Mr Thornley-Taylor's Report-Groundborne
Demolition Noise, Para 9.20 (WESTTCC-14805-086). Back
48
Committee Ref: A59, Mr Thornley-Taylor's Report-Construction
of the Escaltor Shafts, Paras 3.9 to 3.10 (WESTCC-14805-070). Back
49
Committee Ref: A59, Mr Thornley-Taylor's Report-Work in the Basement
of 2-4 Dean Street , Para 9.23 (WESTTCC-14805-086). Back
50
Committee Ref: A59, Mr Thornley-Taylor's Report-Construction
of the escalator shaft beneath 3 Soho Square/7 Dean Street, Para
9.25 (WESTTCC-14805-087). Back
51
Committee Ref: A59, Mr Thornley-Taylor's Report-The construction
and operation of grout shafts in Soho Square, Para 9.28 (WESTTCC-14805-087). Back
52
Committee Ref: A59, Mr Thornley-Taylor's Report-Groundborne noise
and vibration from the operation of the escalators, Para 9.34
(WESTTCC-14805-088). Back
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