Bent stuff
It’s been a couple of weeks since my last blog thanks to TMR 1 consuming my time and then I was away for a week.
Life on site has been interesting…
Yesterday a man got 5 minutes into the induction before asking for written, signed confirmation that if PC Harrington go under (which they have), Sir Robert McAlpine will pay him. We couldn’t offer that, so he left.
On a slightly more technical note I have spent most of today trying to work out if the sheer pile wall will fall down if I take a corner prop out. The prop is really bent. It was hit by an excavator during the dig. It’s meant to be straight and connected to the capping beam each side by a plate and some fairly serious bolts. Since the beam is as bent as it is, I think that it’s load bearing capacity will have been severely reduced. Which temporary works are designed to withstand impacts, this was a big one. Look at the deflection! Additionally it would appear to have lifted away from the capping beam at each end, so isn’t in proper contact anyway. Also the inclinometers, prisms and google maps so no movement on the sheet pile walls. So I think it isn’t really carrying any load. However I can’t prove it. And without an ability to prove it, no one will take the risk on taking it out.
Beam as installed
Beam post strike
So instead the subcontractor will be required I box around the beam. Wait for the concrete to cure enough and then allow the slab to take the strain before the beam can be removed.
In other news we’ve just changed caterers in the canteen and the lunch menu has significantly improved!
Holdfast Training Services Trial Blog 
That’s a complete contrast to the (with out sounding cowboy) ‘it’ll work’ attitude on my site. I’ve just posted a blog with a photo of a bent waling. Regardless of the bend and the fact that its axial strength will have reduced significantly nothing is being done about it. The weld was checked and the piles cleared to carry on – Engineering Judgement. When we dug out the first cofferdam we got to the depth of the lower waling, the wall deflection was measured and surprise surprise there was little movement so the call was made (with out designer authorisation) to leave the waling out and dig to full depth and blind – Engineering Judgement.
Guz, nice post. What was the logic in the design to put it in, has something changed to now make it not required?
Thoughts:
1. What/how is the capping beam connected to the sheet piles? At the near end it looks like the capping beam just ends, effectively transferring load through shear to the sheet piles?
2. What are the sheet piles designed for? It looks like the ranking prop spacing is greater that the midway distance between the final prop and corner, therefore I cannot see why the diagonal strut is in? Assuming the capping beam is acting as another prop at the end (notwithstanding point 1).
3. a free body diagram with resolution of forces and moments might help to persuade those against (assuming the system works without the prop).
4. The slab to be cast, is it at capping beam level? How is the slab going to connect to the capping beam and how will it fit around other raking props? If same issues elsewhere what is the removal plan for the other props?
Damo, thank you for the awkward questions!
The capping beam at the near end will connect to a concrete retaining wall that hasn’t been built yet.
In the long term the piles are primarily for groundwater control. All the clutches are welded and a puddle flange has been installed at foundation level to provide a seal. In the short term they’re there to stop the buildings above falling into the hole. In the original design very few of the props were there. They were a later addition when the toilet block fell off the pub that backs into the site in another corner. There was concern over the stability so they stuck in some extra steel. I can’t find any calcs for it so doubt they were done.
The podium slab is at capping beam level, pull out bars (kwick-a-strip) were cast in at the time for this. The later addition of the corner beam is in the way.
I think the reason SRM aren’t putting too much effort into solving this is because it’s not our problem. It’s in the way of the sub contractor and any delay due to faffing about with extra form work will hit them first. We’ve given them a solution, it’s not sophisticated but it works: box it out then when the slab around it is hard enough take it out and fill in the gap.
Guz, we are using halfen kwika strip in my capping beam – great invention!
Only a couple more questions. Are you monitoring the capping beam deflection? If so did it indicate the sheet piles had deflected, thereby providing evidence for the pub toilet movement? If not monitored before, are you doing so now?
We are monitoring now, but they weren’t when all that was going on. We’ve been monitoring since December and nothing as moved more than about 7mm