Select Committee on the Crossrail Bill Minutes of Evidence


Examination of Witnesses (Questions 12280 - 12299)

  12280. LORD BROOKE OF ALVERTHORPE: How high?

   (Mr Berryman) Four metres. The reason is that the stresses in a wall like this go as to the square of the height, so if you double the height you increase the stresses by fourfold. During the giving of evidence by Sir Keith Bright he suggested that a wall of 1.5 metres would be satisfactory and I did a bit of structural engineering (I am actually a structural engineer) and came to the conclusion that that would, roughly speaking, overload the existing wall by a factor of two. The point I am getting to is that just sticking something on top of this existing wall does not work even if it is only 1.5 metres tall; the wall is simply not strong enough to take that additional load. Whatever height we did, we would have to independently find such a screen or a noise barrier and that would either mean doing something on the street side, which would be possible—it would need to be piled and it would need substantial steel work—or something on the railway side, which is what we have drawn on this sketch. Obviously there has not been detailed designed but it has been looked at by our structural engineers Messrs Scott Wilson and we are reasonably confident that some structure of this sort would be needed. We estimate that for a four metre high wall the total cost of building this structure on the whole length of that wall would be about £5 million. For a 1.5 metre wall it would be much less, but I do not know how much less it would be. Although the barrier itself only costs something like £600,000, the structure which would be needed to hold it up would cost very much more than the barrier would.

  12281. LORD SNAPE: Are you saying you do not approve of Sir Keith's £90,000 somehow or other?

   (Mr Berryman) No.

  12282. I saw you wince a bit!

   (Mr Berryman) In civil engineering terms £90,000 does not go very far.

  12283. CHAIRMAN: It is not your wall anyway.

   (Mr Berryman) It is not our wall anyway, it is Network Rail's wall. I have to say, we have not run this past Network Rail at all so we have no idea what their reaction would be.

  12284. CHAIRMAN: Is it within the limits of deviation? I suspect it is not. You cannot do any work on this under the Bill, can you?

  12285. MS LIEVEN: Where we got when we investigated was that some of it was and some of it was not. I do not think the entirety of it is. To some degree we are not relying on that technicality because we could ultimately promote a separate order or something. It just does not work quite apart from that.

  12286. LORD JAMES OF BLACKHEATH: Ms Lieven, if some of it is and some of it is not, could you define that between horizontal and perpendicular, please?

  12287. MS LIEVEN: Not straightaway, my Lord, but I can try and find somebody behind me who can work it out.

   (Mr Berryman) The limits of deviation are set in plan. It is a question of where the lines on the plan are drawn which shows where it is.

  12288. LORD BROOKE OF ALVERTHORPE: Did Ms Lieven not say that there is a possibility there could be some acoustic work done in the flats at a later stage if in fact the noise levels were found to be high?

   (Mr Berryman) I think Mr Thornely-Taylor is better qualified than I to talk to that, my Lord, but certainly that would be an alternative approach. Mr Thornely-Taylor will cover it in due course. The point that we would make is that the noise levels at the time when the railway opens are not known. There has been a recent significant change in noise levels in this area and there are likely to be more significant noise changes before we build the railway; after all, it is ten years in the future.

  12289. What is the maximum height at which a barrier could be put on top of the wall without the need for all this very substantial additional expenditure?

   (Mr Berryman) The current factor of safety is roughly 1.4. The factor of safety with a 1.5 metre wall is about 0.5. We could start drawing a graph and establish what is the maximum that we could put up but it will not be very much.

  12290. MS LIEVEN: If you were to build the retaining part of it, the steel columns on the pavement side and then stick a noise barrier up above—I know you are not a planning witness but I will use you, if I may, to answer this question—is that likely to raise issues with the council about the impact on the Conservation Area?

   (Mr Berryman) As you will know, the wall does add significantly to the Conservation Area; it is rather an attractive wall in fact. I think the local authority would have concerns about the impact of such a barrier or wall on the Conservation Area, in particular on this wall.

  12291. What about the impact on trees of putting the barrier up there?

   (Mr Berryman) This is for a four meter barrier. If you put a shorter 1.5 metre barrier up you probably would not need to do what is shown on this cross-section to the trees. You might get away with it without too much difficulty.

  12292. Let us move to the possibility of putting the steel retaining structure on the side shown in this drawing, that is the railway side. Can we just put up a photograph taken from the railway side?[16] Can you just explain what difficulty, if any, there would be in supporting an acoustic barrier on top of the wall from the railway side?

  (Mr Berryman) The difficulties would be exactly the same. It is a mirror image whether you put it on one side or the other. The stresses induced in the wall will be identical. To take the load down to an adequate load bearing position you would need to put the columns down to roughly the level of this track bed (indicating). There would be major issues with this. I think Network Rail would be unhappy about this. As you can see from the photograph, the wall actually supports a number of their communications cables and they would need to be rerouted and so on. On the railway this tends to be a very expensive and complex operation. So I think there would be difficulties with that. There is also a track here which I think is the empty carriage road which is used to bring—I had better not say that, my Lords, because I am not absolutely sure, but I think this track is in regular use.

  12293. CHAIRMAN: It does look very used.

   (Mr Berryman) This one is certainly used, my Lord. That one may or may not be; I am not sure you can tell from this photograph.

  12294. MS LIEVEN: Assuming that the track next to the wall is not used very much at all but the one closest to the photograph is used, if one was going to put the retaining structure on this side—on the trackside—would that involve possessions of the railway?

   (Mr Berryman) You would certainly need to take possession of the adjacent track; you probably would not need the whole width. You certainly would not need the whole width but you would need to take possession of this track.

  12295. LORD BROOKE OF ALVERTHORPE: Could I just interject with another question?

  12296. MS LIEVEN: I think I am not going to be able to answer the question about whether the wall is within the limits of deviation straight off, so those are all my questions, Mr Berryman.

  12297. LORD JAMES OF BLACKHEATH: Mr Berryman, we are concerned about the number of leaves on the line. Can you tell us: are these the right sorts of leaves or the wrong sorts of leaves?

   (Mr Berryman) As you may know, Network Rail have been making strenuous efforts to chop down all the trees which give off the wrong sorts of leaves. I really do not know, I am sorry.

  12298. LORD JAMES OF BLACKHEATH: We have not got a third rail there either, have we?

   (Mr Berryman) There is no third rail at all on the north side of London, my Lord.

  12299. Has anybody given any thought or any costings, or would it be feasible to simply put bricks on top?

   (Mr Berryman) That would give us exactly the same problem as putting a steel structure on the top, my Lord. The thing which governs this kind of wall is the wind-load. Whatever kind of structure you put up it will still attract the same wind-load.



16   Crossrail Ref: P79, View of retaining wall from trackside (SCN-20080507-015) Back


 
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