Cakes and Pipe Jacking
I have been rather quiet as I realised that all I seemed to be writing about was what size cast iron pipe we unexpectedly uncovered on our drainage run and what was going on with the latest in the HV cable installation saga. Well nothing has changed there we are on big old cast iron pipe number 6 in the last 10m of drainage, the client are getting excited about us damaging the HV cables and we are now extended the HV sub station slab because they put the wrong size GRP housing on top of it.
At the end of last week we had a team meeting to discuss roles and responsibilities as the Project Director has realised that they may have scrimped too much on construction management staff. We have no resident temporary works engineer or quality assurance person and these are the areas that the project are crashing and burning. At the start of the week I was looking at a promotion to being the resident engineer of the block G construction-think Ex COFFERDAM but 40m wide and 100m long with 2 stages of propping! In the initial meeting I pointed out that they might want to consider the detail of the connection of the waler to the sheet piling as they were suggesting a 1m gap to allow the construction of columns. They said not to worry about it as they would use wedges, until I pointed out that wedges spanning 1m taking vertical components of the forces probably wouldn’t work! So they went back to the drawing board and asked to move the columns in a bit!
OIC Power and Drains again! But this is taking an interesting step as we are planning our pipe jacking exercise to tunnel under Battersea Park Road. In a nutshell the masterplan is to build a cofferdam to launch the pipe jacking machinery to cut a 70m tunnel approx 5m BGL to meet with an existing sewer on the other side of Battersea Park Road. watering scheme.
Pipe jacking launch shaft in top left corner tunnelling 68m with the final 30m under a raised section of the Battersea Park Road bridge: and a typical pipe jacking launch shaft:
General works:
The main issue is one of John’s favourites: GROUNDWATER! In the foul drainage run we have had to sump pump a considerable amount of water flowing through the Terrace Gravels, which is also slightly tidal as we are about 300m away from the river.
The plan is to control the groundwater with a de-watering system:
Likely issues:
-Proximity and state of dilapidation of the Battersea Park Road Bridge.
-Proximity of Network Rail lines.
-Risk of settlement of bridge foundations.
-Risk of encountering unknown services or obstructions.
-BOUNDARIES/PROPERTIES-although we can’t be tunnelling through much worse than the gravels which will be pouring water in! Unless we hit an old brick pile or more of the old gas works infrastructure.
-GROUNDWATER-we are pretty much in the worst case scenario.
-CONTAMINATION-So far we have been OK with de-watering around the site so fingers crossed it can just go down the foul sewer.
Without looking at my notes they were the main points I remember from John banging his hand against the wall! No doubt I will have more to write on this over the next few weeks.
On a plus point I held a Colossal Cake Sale for Help for Heroes in the canteen and we made £220. I mentioned to our Environment/Schools/PR person that I could come in uniform and she held me to that offer. The problem was mine was all in the attic in Poole. So after a quick cycle to a friend’s house 5 miles away I squeezed myself into an ex-Army Air Corps Adjutant’s tailored(!) green kit to sell our cakes for an hour. I was overwhelmed by the generosity of some of the guys on site and the support from both the managerial staff and groundworkers. Not a bad outcome for a couple of hours work.
Holdfast Training Services Trial Blog 
All interesting..I have a basement excavation a km north and west of you there in the Kempton Park gravels which skirt the southern part of your site and along Battersea Park Road – very interesting – 3 m beep excavation – stood vertical stood dry – fairly stiff. So although nominally a coarse grained soil…..acted like a fine grained one…if there was a groundwater level we never found it.If I were pipe jacking there what would I do about the threat of groundwater?…I’d look at any piezo data for b/holes around the crossing – and when these didn’t tell me anything I’d go for a low yield dewatering system – but here’s the rub would it be traditional or injector…..I leave you to ponder but if you get 10 l/s out of that I’ll eat a complete HfH cake and donate the cost
We have had water pouring through our deep drainage trenches that are now getting on to 5m deep. I had to ask the supervisor to be honest and confess if they had broken a water pipe as it was pretty clean too! I think the first few metres have been similar to what you described but the gravels we are now in could be sold at B&Q to make your driveway! The borehole data has been interesting too as the nearest one showed no groundwater for the first 11m despite our drainage gang paddling in their trench about 30m away. I concluded that they were using water as a lubricant to get the BH to 45m for the Northern Line Extension (NLE) and that they weren’t that interested about the groundwater near the top. I also tried to come up with a design borehole using the other NLE data and it shows evidence of the old reservoir beds from when it was a waterworks. I will give Neil a copy when he visits next week. I found out quite a lot about the history of the site for my TMR which makes at least the first page an interesting read!