Innovative piling works at Half Tide Dock, Liverpool
Liverpool’s Half Tide Dock is one of the final developments to be completed before Liverpool gains its European Capital of Culture status in 2008. Geotechnical specialist, Bachy Soletanche Limited provided an innovative piling solution that was specifically designed to preserve the heritage dock wall adjacent to the site.
Liverpool is a city renowned as a hive of commercial and industrial activity, but since the announcement in 2003 that the city would be the European Capital of Culture for 2008, the level of enterprise and animation has risen to a new peak.
The residential development will form part of the final stages of the city regeneration programme that precedes Liverpool’s capital of culture celebrations; a programme that has seen the city evolve dramatically over the past five years.
Situated in the popular waterfront location on Liverpool’s dockside, the £180,000 piling project will support the construction of a nine-storey luxury apartment block, due to be fully completed late this year. The prestigious development will comprise one hundred and twenty-one residential apartments, accompanied by underground parking.
At first glance, the project seemed to require a straightforward piling process – but the piling work was destined to be far more complex once the heritage status of the nearby dock wall had been identified. However, Bachy Soletanche Limited (BSL) provided a solution that would stand firm – developing a bespoke design that would prove ensure there was no displacement of the ground surrounding the piles.
“Once we were made aware of the heritage status of the dock wall, it meant we had strict deadlines to adhere to, and the wall was not to be affected in any way from the nearby drilling and pile construction.” Commented Steve Mallinson, Contracts Manager, at Bachy Soletanche Limited.
“As such, we installed permanent steel liners of 750mm diameter for the piles that fell in close proximity of the wall – ensuring the development had the required level of support whilst preserving the integrity of the heritage dock wall” He explained.
The new design meant that seventeen out of the total eighty-four piles were constructed using permanent steel liners surrounding the main body of the pile, each 750mm in diameter. The liner effectively debonded the pile around the top 10metres of the full pile length – ensuring no load was transferred from the pile to the surrounding ground, and hence the dock wall.
To insert the permanent steel liner, the normal LDA process was used for boring the hole – of which a temporary casing was inserted to drill the pile. Then the permanent steel liner, in effect, a thin wall casing was attached to the cages and put in place once the pile was drilled. Then the pile was concreted and the temporary casing was lifted out.
Steve Mallinson commented:
“By constructing the permanent steel liner around the piles, we could ensure that no load would transfer between the pile and dock wall. As such, no impact was made to the surrounding area at any point of the process and the strict guidelines for protecting the wall were adhered to fully.”
The first row of piles, which ran parallel to the dock wall consisted of seventeen large diameter (LDA) rotary piles, each with a depth of 14metres. It was for this initial row that the steel liner process was used. The piles were bored with a 10metre rock socket, of which 7metres was debonded with the liner, as the initial 3metres of ground was ‘made ground’.
The remaining sixty-seven piles were constructed using the faster continuous flight auger (CFA) process, with piles bored to a depth range of 8-9metres - altogether providing a short section of a contiguous piles wall and the CFA bearing piles.
The transition between the CFA and LDA piling process involved the work to be undertaken with a multi-disciplinary rig and crew. The rig, a BG-18 completed all the CFA piles and was then converted to rotary mode on site to complete the LDA works.
Steve Mallinson continued:
“The combination of the CFA and LDA piles alongside the bespoke design allowed the project to run smoothly and within the four-week deadline. Although, we did have to consider the timings for the LDA piles as the construction of these piles is far more time consuming than the CFA process. It can vastly reduce daily pile productivity which is one of the reasons why the LDA piles were constructed last”
“However, this project is a great example of how bespoke designs can bring huge benefits to smaller contracts, as well as the larger projects with which this type of intricate process would be more commonly associated.” He added
BSL has also completed a range of works throughout Liverpool as part of the city’s ongoing expansion, including high-profile work at Kings Waterfront on the other side of the River Mersey, which was completed in February 2006.
Steve Mallinson explained:
“Bachy Soletanche provided piling for the arena and conference centre at the Kings Waterfront project, as well as the multi-storey car park to be situated on the site, in a two-phase project worth a combined £3.2million. Much larger than the work at Half Tide Dock, the piling work included 800 CFA piles and 420 LDA piles constructed within a four month schedule.”
“The Liverpool 2008 European Capital of Culture has been an excellent opportunity to regenerate the city and we at Bachy Soletanche are delighted to have been such an active part of it” He added.