Back in the game!
Well I made it back to London this week and back to work on Monday. The foot is on the mend and I have now progressed to the B3 Cbt Engr post final exercise hobble! All of my x-rays have now come back fine and I am now encouraged to walk but it is still a bit uncomfortable. It takes me twice as long to get to work as I have to walk slowly to the bus stop and site office but hopefully it will be back to whacky races on the bike again soon. At least my foot looks like a good bit of engineering now with it’s 3 titanium bolts!
I am now office bound for a few more weeks until I can squeeze the hobbit foot into my work boots but I am still covering the utilities installation. I have picked up a few technical issues that need sorting out before we can finish off our drainage. We are planning to pipe-jack a 450mm concrete pipe 70m under Battersea Park to the mains sewer. Our sub-contractor (O’Keefe) have a sub-sub-contractor (Perco) lined up to do the work and as far as we were concerned they had a plan at least pencilled in. I was a bit concerned to see an email from Perco asking O’Keefe to clarify the ground water level as the latest and closest borehole information didn’t show a GW strike in the first 10m yet another borehole further up the site hits water around 3m BGL. I found this latest borehole data very unusual as around 20m away we had been striking water at around 3m in the drainage trenches and it was p*****g in! So today I have been doing my own desk study and gathering previous borehole information that is on Aconex-our data sharing site and getting the latest data from the client’s representatives. Low and behold all previous boreholes along the south of the site strike water at around 3m BGL either in the River Terrace Gravels or Alluvium Clay above the gravels. The area at the south end of the site is a bit unusual as it was a reservoir with filtration beds in the 1800’s and the back fill has been a variety of materials. I think the latest borehole didn’t record the groundwater accurately for perhaps 2 reasons: they were using water between 1-5m to lubricate the cable percussive borehole machinery, or the fact that we were dewatering our drainage trench around 20m away at a rate of 7L/s. Either way it doesn’t look like a good borehole to use for design (John-triangulation I hear you say!). I am also a little concerned that Perco have said that they would have problems conducting pipe-jacking with a heading in wet granular soils due to the likelihood of ground loss. I have put my findings to the senior engineer at Buro Happold who has been designing the drainage and hopefully he comes back with some advice on the design borehole that Perco should be planning the works to.
Around the rest of the site progress has been made and here is last months time lapse video:
http://vimeopro.com/user25873713/battersea-power-station
In the Cam 96 video you can see my retaining wall for the road going in by the railway arches. In the bottom left the cofferdam for the pumping station has been excavated and propped using a Mabey prop system and finally the concrete rings have gone in but I missed that excitement. In the top left corner John would be getting excited with the props, waling, thrust blocks and excavation of the cofferdam, so far the sheet piling has moved 20mm and there is only 5mm more allowed. We are not sure how accurate all the monitoring measurements are though because someone has hung a water pipe on the wall using the survey targets! The piling rigs are still working hard and the sub-contractors are still constantly arguing over pile mat handover and areas to work in.
Holdfast Training Services Trial Blog 
Angie
Glad to see you are back at work. In case you missed your last Blog’s comments If you run out of things to do
Contracts/Commercial
QA v QC – ISO 9001
Sustainability Issues
H&S issues
Let me know when you are fit to visit
Kind Regards
Neil
Ah Ha! A foot with eight nails, one on each toe and three spare!
Are you anticipating pipe jacking in the alluvial clays or the terrace deposits? What sort of jacking rate do they anticipe i.e how long would the ground be unsupported and how long would it remain undrained for? Is headloss really a significant risk? Can you tell me how the Perco set up operates?
Well that is all still TBC. From the borehole data I dug out it looks like under the watertable in the terrace gravels. Initially they were going to jack a 1.2m steel or concrete casing to enable access for miners to hand dig if required. 80m was going to tale 3 weeks. Now that it is wet gravels they may need to auger bore. Perco would like to see a trial hole before making a decision but the drainage down that end has now been backfilled. It is quite annoying because they are being employed by the sub contractor who have been doing all of the drainage. I would have thought this would have come up in conversation weeks ago when their project manager first contacted them!
Classic illustration of understanding the purpose of the SI – you’re not too fussed in what’s going on at 10-20m down, just 1.2m so the ‘CMT’ brief is somewhat different and a couple of hand dug trial pits would suffice. Clearly if plant is on hand and spare sappers are not it will be machine excavated. Quick utilities check anc cat scan, dig, look and back fill. No one will enter the hole so shoring probably not required. Don’t dig exactly on the alignment or you’ll be jacking through your own made ground… But this is not your problem…
You have contracted out the work to others and they have then subcontracted part onwards again so, in all, it’s their plan and their cost. You’re iterested in ensuring it is safe and delivers the specified end product to time, quality and budget. Request and require briefing on their proposed processes and schedule and keep the pressure on them to make sure they deliver!