CASE STUDY: RESTRICTED ACCESS PILING, DALSTON WESTERN CURVE.
Project: Installation of augered piles within the existing tunnels for upgrade of rail services.
Location: Dalston Western Curve, East London
Client: Transport for London
Main Contractor: Birse Metro
Project Overview
The Dalston Western Curve is an important part of the upgrade work for the East and North London lines in preparation for the Olympics. The new Dalston Junction station, which opened earlier this year (2010), forms part of the East London Line extension, and the curve links it with Highbury and Islington station on the London Underground Victoria Line. Dalston Junction and the existing Kingsland station will now link to Stratford and the 2012 site.
The logistics of this scheme were very complex, on the site of an old railway with existing bridges supporting roads and buildings constructed above. The piling, required to support new walls that divide the north and south sections of the bridge, was one of the trickier aspects of the job and working in less than 5m of headroom, we piled to a depth of 19.25m.
Sectional flight auger piles were used with temporary casings in the top to retain gravel and water. The casings were removed once the concrete had been pumped into the pile bore. Due to the restricted access nature and the depth that we were drilling, we opted to use short masted Klemm rigs.
"These are powerful, high torque rigs, ideal when you've got the restrictions we experienced here and the loads dictate a larger diameter pile to a greater depth," says Divisional Managing Director, Dave Warner. Birse Metro's Project Manager, James Renwick explained "Next to the tunnel where Van Elle piled is what is known as the narrow covered way. It is being used to transport all the vehicles and equipment whilst piling is going on. The big issue here is that we have a lot of big plant and people moving about with no way to segregate it other than for each piece of machinery to have a man with it."
All of the single to three storey buildings in the vicinity were compulsorily purchased by TFL so these could be demolished as part of the scheme and the A10 (Kingsland High Street), supported by the bridge, was closed one lane at a time so as not to impact more than necessary upon commuters. This is why it was key that the piling went ahead, and was completed, within planned programme scales. Unfortunately, as Crossrail will eventually run beneath and there is a 10m deep intrusive limit in certain areas, the entire site could not be piled. Dave Warner said "In an ideal world, the platform would be the same as the finished pile level, but in this case, to allow us to physically get the rigs in, the platform was formed lower requiring each pile to be built up slightly."
Understanding the timescales and restricted access, rail-specific issues involved on this project allowed us to utilise the best rigs for the job, maximising the effectiveness and efficiency of the piling despite the difficult working conditions. Birse Metro were very happy with our proposed solution and the specialist advice we gave. The piling was a major part of this scheme which went on to be completed months ahead of schedule. Through careful planning, safe working and the relationship we built with the client/project team we were able to improve on the proposed time frame allowed for the piling and testing. The project value to Van Elle was £550k.
1) 127No. 600mm diameter Sectional Flight Auger piles, all with temporary casings for the first 3m. 32 piles are 19.25m deep. 71 piles are 17.50m deep. 24 piles are 13.50m deep.
2) The concrete used was C35 class DC-1
3) Two Klemm rigs were used, a 709 and a 708, both of which have short masts to operate in 5m headroom. The Klemms are multi-purpose drill rigs with rotary heads and hydraulic drifters. The heads allow for up to 40kNm torque and 13 Tonnes Retraction force.
