Examination of Witnesses (Questions 400
- 419)
400. MS LIEVEN: Thank you very much.
401. CHAIRMAN: Professor Mair, there
will be a number of Petitioners who want to talk about particular
buildings, some of them listed buildings. I am not asking you
to do anything about it now but will you be prepared to have a
view about what the effect might be on those buildings? We are
going to see some of them this afternoon—Whitechapel, Hanbury
Street and so on.
(Professor
Mair) Yes, of course.
402. I think it is inevitable that the Petitioners
will want to ask your opinion about what is likely to happen to
their building.
(Professor Mair) I will be pleased to.
403. MS LIEVEN: My Lord Chairman, if
I can just outline to the Committee, in the other place Professor
Mair was never actually called as a witness, apart from giving
the presentation, because, in the main, we found it appropriate
for Mr Berryman to deal with site-specific settlement issues where
we felt that that fell within his very extensive area of competence.
If there are specific issues where we feel it is necessary to
call Professor Mair we will do so, but we hope—particularly,
I have to say, because of Professor Mair's availability—the
Committee will bear with us if we choose which witness seems most
appropriate to us at the time.
404. CHAIRMAN: I think we are entirely
in your hands, Ms Lieven. What we have heard this morning is extremely
interesting to us all and we realise the great expertise that
you are bringing to bear. Anyway, we will see what happens.
405. MS LIEVEN: Thank you, my Lord.
406. CHAIRMAN: I have one other question:
how do you get the tunnel-boring machine in? I can quite see that
it goes through the portals, but I see that you talk about chambers
as well. If it is introduced halfway along the route of the tunnel
what is involved in that process? They are pretty big machines.
(Professor
Mair) You are absolutely right, they are big machines. In large
part, the tunnelling machine is erected underground.
407. It comes in bits?
(Professor Mair) It comes in bits, that
is right, so it can be erected in chambers from shafts underground.
408. So the lorry traffic is not likely to be
"abnormal loads".
(Professor Mair) No, not certainly bringing
in the entire tunnelling machine as you have seen in the diagrams,
no.
409. BARONESS FOOKES: My Lord Chairman,
I have one query on the actual type of soil. You have in one of
the earlier geological sections something called the Lambeth Group.
Is that something quite different from London Clay? It seems to
be in two shades.
(Professor
Mair) You are right, it is different from London Clay. It is in
two shades—a sort of darker brown and a lighter brown—to
broadly indicate that the upper part of the Lambeth Group tends
to be stiff, strong clay rather similar to London Clay but, if
anything, stronger. The lower part tends to be sands.
410. From the layman's point of view you have
a bigger layer of clay than would appear at first sight.
(Professor Mair) Yes, that is correct.
411. The other question I wanted to ask: all
your illustrations were for tunnels coming into an area where
there were no other tunnels, but, of course, we know that the
whole thing is criss-crossed with existing tunnels. Does that
have any effect? Presumably not or you would have mentioned it.
(Professor Mair) Well, it is very important.
You are absolutely correct, the presence of other tunnels is a
very important consideration, and when the new Crossrail tunnels
are constructed beneath existing tunnels then there has to be
a very careful assessment of what will happen to the existing
tunnel. It will be subjected to potential settlement, and there
has to be a very clear evaluation of that to ensure that the existing
tunnel is not adversely affected.
412. There could, presumably, in theory at least,
be considerable damage.
(Professor Mair) In theory, but it would
be absolutely the case that that would never be allowed to take
place. You are completely right; if, for example, it was a running
London Underground tunnel then it is very important to London
Underground and to the population at large that the operation
is not in any way impaired. So, therefore, the amount of movement
must be restricted to a suitably small figure.
413. LORD BROOKE OF ALVERTHORPE: Which,
Professor Mair, is the most expensive method: the pressure balance
machine or the spray-concrete lining? Is that a factor which is
taken into account when determining which should be used?
(Professor
Mair) It is a difficult question to answer straightaway because
the machine tunnelling, the earth-pressure balance machine tunnelling,
will be used for the smaller size for the running tunnels—the
7-metre diameter running tunnels—whereas the sprayed concrete
is used for the much bigger station tunnels. So it is not immediately
easy to compare the two in terms of cost.
414. The sprayed concrete was used in the Channel
Tunnel primarily, was it not?
(Professor Mair) It was used for the crossovers.
Do you mean the Channel Tunnel itself as opposed to the Channel
Tunnel Rail Link?
415. The Channel Tunnel Rail Link.
(Professor Mair) The Channel Tunnel Rail
Link, linking from Folkestone up to St Pancreas, used both techniques:
it used spray-concrete in parts and it used earth-pressure balance
machining in other parts—for both. Both methods were used.
416. I am trying to work out in my head, when
you start with a gleam in your eye, what is the driving force?
Is it, in fact, trying to avoid or minimise the amount of disruption
which might arise from it, or whether it is a cost factor which
is the prime driver?
(Professor Mair) Do you mean in the choice
of tunnelling technique?
417. Yes.
(Professor Mair) I think it is both. Both
techniques minimise the amount of settlement. As I explained earlier,
the station construction—if you use sprayed concrete it
gives you much more flexibility because you do not have to stick
to circular tunnels.
418. I am just wondering if someone could come
and argue that their property was going to be disrupted or their
big commercial development was going to be disrupted and they
would prefer you to go for a different type of tunnelling method
because it would be less disruptive.
(Professor Mair) I think they would find
that argument hard to pursue. Both methods that we have been talking
about this morning produce very small volume losses and very small
settlements.
419. But the sprayed one more than the earth-pressure
balance machine.
(Professor Mair) Yes, the sprayed one
is more. That is correct. It could be argued that stations should,
therefore, be constructed by tunnelling machine rather than spray
concrete. This would require a lot of thought because stations
are not very long—typically only a few hundred metres long—and
they do not lend themselves well to a tunnelling machine which
is much more suited to a long drive.
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