Examination of Witnesses (Questions 5620
- 5639)
5620. MS JONES: Thank you. Would you
like me to do that now, or shall I go on to my settlement issues?
5621. CHAIRMAN: I should deal with it
now.
5622. MR TAYLOR: My Lords and my Lady,
I am going to call Mr Thornely-Taylor to give some evidence in
response to the points raised by Ms Jones, if I may.
5623. CHAIRMAN: Have you got a particular
proof of evidence for this point?
5624. MR TAYLOR: We do not. I was going
to proceed in the way we did last week and ask a number of short
questions and ask him to verify them.
5625. CHAIRMAN: You do that and then
Ms Jones can ask hers.
MR RUPERT
THORNELY-TAYLOR,
recalled Examined by MR
TAYLOR
5626. MR TAYLOR: Mr Thornely-Taylor,
can we start please by referring to Information Paper D10.[3]
I want to begin by looking at paragraph 2.9. Here is set out the
policy that is to be adopted with regard to the design of the
permanent track support system. We are going to require the nominated
undertaker to design the permanent track support system so the
level of groundborne noise near the centre of any noise-sensitive
route is predicted in all reasonably foreseeable circumstances
not to exceed the levels in Table 1. If we can turn please to
the previous page to Table 1 we can see the first criterion set
out for residential buildings, reference to 40 dBLAMax,S?
(Mr Thornely-Taylor) Yes, indeed.
5627. The first question, Mr Thornely-Taylor:
is that 40 figure a target to design to, or not?
(Mr Thornely-Taylor) It is a target to
design to for as much of the tunnel between the portals as possible.
It is not the target that will apply piecemeal along the route.
It will not be possible for a contractor to choose cheaper and
cheaper track because he has got more and more headroom above
the predicted noise level. He will be required to select, as is
said in 2.9, a track support system which as much as possible
from end to end of the tunnel section will achieve 40. It follows
from that that for most of the length between the tunnel portals
it will be much better, because it will have been selected to
achieve 40 in the most difficult circumstances.
5628. Thank you. Why has 40 been selected as
the appropriate noise criterion?
(Mr Thornely-Taylor) 40 is a level above
which complaints have occurred in the past from groundborne noise
from underground railways. It has to be said the situation in
the past has been that when that has arisen there has also been
vibration that you feel with the sense of touch. Vibration is
not expected to be discernable by people above Crossrail. In any
case where we did come close to 40 the position would not be the
same as in those cases I referred to where there have been complaints
in the past from the older style of railway.
5629. Before we leave IP10, there is reference
in paragraph 2.9 as we have seen to a prediction in all reasonably
foreseeable circumstances. On the third line of paragraph 2.9
you can see a reference to a prediction "in all reasonably
foreseeable circumstances". Why are those words included
in the policy?
(Mr Thornely-Taylor) Because it is not
impossible that, in the course of constructing the tunnel, a feature
is encountered underground which was not foreseen, not on the
drawings, not known about, which has the effect of transmitting
groundborne noise and vibration more efficiently than the normal
ground conditions that were assumed. It is not impossible that
in a particular location a higher level of groundborne noise might
occur than was the design objective.
5630. CHAIRMAN: Can you give us an example?
I know this could happen with piles but we are not talking about
piles here.
(Mr Thornely-Taylor)
A good example would be either the appearance of a boulder within
the clay that the tunnel was being bored through, which lay between
the tunnel and some building foundations, or a feature of underground
London is that there are many old, forgotten, disused other tunnels,
other structures buried beneath the ground that we do not know
about, and we could find unexpectedly that there was a rigid structure
between the top of the tunnel and a building that was noise-sensitive,
hypothetically.
5631. MR TAYLOR: In the modelling work
that has been done to date what approach has been adopted to address
that sort of uncertainty?
(Mr Thornely-Taylor)
The modelling work, as I explained on day one, has addressed uncertainty
by comparing modelled results for existing railways using the
same model in more than one set of circumstances; and the conclusion
of that approach was to decide that an uncertainty margin of 5
dB LAMax,s was necessary to add to the predictions that have been
made to allow for unforeseeable influences which might result
in higher noise levels than those which the model predicts.
5632. CHAIRMAN: Is that within the 40?
(Mr Thornely-Taylor) Yes, what flows from
that is when a prediction presented in the Environmental Statement
is, for example, 40—in fact there are very few as high as
that—then the actual model prediction was 35, it had a blanket
5 added for uncertainty.
5633. MR TAYLOR: Thank you. While we
are still in the Information Paper D10, can we just deal briefly
with the point about the maintenance of wheels and track. We can
see at paragraph 2.10, Mr Thornely-Taylor, that the Information
Paper explains that: "the nominated undertaker will put in
place measures that will ensure that the track of the underground
sections and the wheels of the vehicles operating the Crossrail
passenger service are maintained in a state which under all reasonably
conceivable circumstances will lead to adequate control of groundborne
noise and vibration arising from the railway". If we go over
the page to paragraph 2.11 there is a reference to requiring the
nominated undertaker to ensure that the "rails of the underground
sections are conditioned by grinding or other suitable means and
are appropriately maintained thereafter". What is the approach
that the Crossrail project is taking to the issues of maintenance
of track and wheels?[4]
(Mr Thornely-Taylor) These are important issues
because the level of groundborne noise above an underground railway
is very strongly dependent on the condition of the rail running
surface and the wheel treads and this commitment in IP D10 is
an important part of the whole approach to achieving actual low
groundborne noise and vibration levels.
5634. Thank you. I am going to ask for the noise
contour map to be put up.[5]
Again, I believe you referred to this last week, Mr Thornely-Taylor,
on Day Eleven at paragraph 4275, for those who are interested,
and if we can move the map slightly to the right so we can focus
on it that way. Thank you. We can see Hanbury Street and Princelet
Street and it is a little difficult to see it, hopefully we might
zoom in slightly. Thank you. Here we have a map of the groundborne
noise contours that are forecast from the modelling work that
has been done. Can you explain what is shown on this drawing,
please?
(Mr Thornely-Taylor) This is the result of
computer modelling, using the methods I described on previous
occasions. With the five units added that I just explained for
uncertainty and it gives the predicted level of groundborne noise
in a standard residential building, very similar to the kind of
buildings in the Spitalfields area, it does actually allow for
a single basement to the building. What is plotted is rather like
airport noise contour, except it is an underground source and
not an overground source and the outermost contour represents
25dB LAMax,s and each contour interval is one unit. If you look
across the Spitalfields area you will not find any contours as
high as 30 so, as a general statement, one would say the prediction
including the five units for uncertainty for the Spitalfields
area is less than 30 LAMax,s.
5635. MR TAYLOR: Thank you very much
indeed. What you are saying to the Committee is that the modelling
work that has been done to date demonstrates that the likely forecast
of impact on groundborne noise within a standard residential property
in Spitalfields is substantially below the 40 criteria in table
1?[6]
(Mr Thornely-Taylor) It is very substantially
below. As we heard in the hotel demonstration, the difference
between the quietest of the trains there which were down around
the low 30s and the loudest that we heard is quite a lot.
5636. CHAIRMAN: Can you remember what
the figure was for the loudest?
(Mr Thornely-Taylor) The loudest was 41.
5637. That is what we thought.
(Mr Thornely-Taylor) My Lord, if I could
explain the reference to 47. I also made a mention when I was
last in this chair, I think, about a property in Spital Square,
which I had been in, over the Central Line and I went there because
one of the residents of Spitalfields had mentioned you could hear
the Central Line in there and it was in the basement of building
that I said the maximum level was about 47. I did not do a formal
survey. That is where the 47 came from. We did not hear anything
like as much as 47 in the Chancery Court Hotel. The loudest was
41.
5638. CHAIRMAN: I think it is just as
well to get that cleared up, thank you very much.
5639. MR TAYLOR: I think I am right in
saying that one of the inputs to the modelling work is an assumption
about the form of the track support that is going to be utilised.
(Mr Thornely-Taylor)
That is one of the most important assumptions. Going back to the
original Crossrail scheme in 1992 a stiffer form of rail support
was assumed then than is the current assumption in the Environmental
Statement and, indeed, as engineering work progresses, it is quite
possible that the stiffness of the rail support for the standard
system will be lower than was assumed in the Environmental Statement
and noise levels will ultimately be less than those included in
these contours.
3 Crossrail Information Paper D10-Groundborne Noise
and Vibration, http://billdocuments.crossrail.co.uk
(LINEWD-IPD10-004) Back
4
Crossrail Information Paper D10-Groundborne Noise and Vibration,
http://billdocuments.crossrail.co.uk
(LINEWD-IPD10-005) Back
5
Crossrail Ref: P23, Noise Technical Report, Hanbury Street/Princelet
Street area (SCN-20080312-023) Back
6
Crossrail Information Paper D10-Groundborne Noise and Vibration,
Table 1 Construction and Operational Groundborne Noise Criteria,
http://billdocuments.crossrail.co.uk
(LINEWD-IPD10-005) Back
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