Product category:
Drainage, Footings and Piling
News Release from: Bachy Soletanche | Subject: Piling project
Edited by the Buildingtalk Editorial
Team on 07 April 2008
Bachy Soletanche piling works at St
George Wharf
Ground engineering specialist, Bachy Soletanche has recently demonstrated its extensive geotechnical capabilities at the attractive residential development, St George Wharf in Vauxhall.
The GBP1.6M piling project was for the final block - Aquarius Building - and required 10 Large Diameter Auger (LDA) piles with diameters between 1,800mm and 2,400mm which were drilled to a massive depth of 60m For an area that was never really 'the place to be seen', Vauxhall has certainly transformed itself in recent years
This article was originally published on Buildingtalk on 5 Feb 2007 at 8.00am (UK)
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The area became particularly popular when St George announced its plans for St George Wharf - the high-profile development only 275m from the water's edge.
Since then, the development has proved to be a great living location for city centre residents, which is why there is much anticipation for the final block to complete later in the year.
BSL was awarded the sub-contract by John Reddington Limited to conduct the foundations project.
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It was recommended that a piling strategy should be put in place to increase the ground's load bearing capacity by between 11,000kN and 45,500kN.
The site is surrounded by buildings, main roads, the River Thames and Vauxhall Bridge which all proved to be vital considerations in the piling solution.
Moreover, the Victoria tube line runs directly underneath the site.
Consequently, BSL created an innovative piling solution to get the maximum load bearing capacities within the site's constraints.
The 10 LDA piles were constructed using an extremely high torque Bauer BG-40 rig.
Vijay Pookat, the Bachy Soletanche Limited Engineer on site commented: "In normal circumstances we would construct several LDA piles using smaller diameters and lengths".
"Due to the underground tunnel running across the site, this just wasn't plausible so we substituted the volume of piles with extra depth and diameter in just 10 piles." These massive piles are installed by drilling down to the depth using the LDA Rotary process with an extra long 'Kelly' bar to provide an extra long pile length.
The temporary casing were then installed followed by the permanent casing.
Once these were in, grout was injected into the annulus (the gap between the temporary and permanent casings) ready for the concrete to be poured within the permanent casing.
The de-bonded permanent casings were a requirement to prevent load transfer into the underground tunnels and escalator shafts.
They were also used to cut off the ground water which is naturally high on this site.
The casings are also suitable for the ground strata which includes 10m of made ground, London Clay, layers of Lambeth sands, clay, and then Thanet sands.
The permanent casings were between 14.9m and 21.5m in length which took them down below the tunnel level and made them extremely heavy.
It was their sheer weight which meant that the annulus between the permanent casing and temporary casing had to be grouted.
The grout also kept the permanent casings vertical, which was extremely important due to the depths in which these piles are installed.
Vijay continued: "Working with piles at such depths, the slightest of movement can cause the piles to go off line".
"If this occurs, the pile is deemed ineffective." For that reason, BSL spent a lot of time carefully installing the piles, taking a week to complete each pile - a testament to their enormity.
Due to the underground obstructions, the piles have been specially placed in order to successfully carry the correct load.
Vijay Pookat explained: "The piles to the south and east of the site were extremely important as these piles fell in line with the Victoria tube line".
"Boring piles very close to and between these tunnels required complete accuracy".
"There was a huge risk of damage to the tunnels if the work had not been completed correctly".
"Consequently the piles required larger diameters and longer permanent casings to stop the piles (and eventually the structure) causing any settlement which could have damaged to the tunnels in the future." With the underground tunnels being so close to the piling works, engineers on site used a monitoring system in order to detect any movement or vibration that may affect the tube lines.
In fact, St George continually measured the deflection of the escalator shaft within the Vauxhall station complex during the piling works.
If this had moved more than 2mm, the escalators would have jammed, stopping the works on site immediately.
There was also a risk of noise and vibration from the piling operations being heard in the station tunnels by passengers, so it was important that these were kept to a minimum.
Tony Pressley, construction director at St George South London commented: "Overall, these risks were managed using expert Ground Movement Engineers to advise St George and London Underground engineers".
"For each stage of works, very detailed Method Statements had to be submitted to London Underground which required extensive discussions between BSL, Reddingtons, St George, GCG and London Underground".
"St George set these processes in place and facilitated the coming together of all parties to ensure a successful outcome." BSL began working on site in October 2007 and completed in January 2008.
Works are now continuing to complete the St George Wharf, Aquarius Building later in the year.
The building is the final addition to the St George Wharf development and includes one and two bedroom apartments.
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