Bachy Soletanche conducts another project for Liverpool’s dockside regeneration
Having completed several highly successful projects in the area, Bachy Soletanche Limited has now clocked up another, completing its on-going work at Liverpool’s regenerated dockside. The project, which saw Bachy Soletanche’s red rigs on the Liverpool waterfront near the Pier Head, is for the residential development, Mann Island Mixed Use Development. Bachy Soletanche constructed a secant wall and bearing piles in a comprehensive piling project.
With one of the best locations in Liverpool City Centre – next to the ‘Three Graces’, Royal Liver Building, the Cunard Building and the green-domed Port of Liverpool Building – the Mann Island Development is set to become a popular living location for professionals in the city. Moreover, it will provide stunning views of the River Mersey and the city itself.
The main contractor, HBG Construction awarded Bachy Soletanche the piling contract with confidence due to the large amount of piling works the leading geotechnical firm had conducted across the Liverpool dockside previously. Such projects included the Echo Arena and BT Conference Centre (Kings Waterfront), two new hotels, a multi-storey car park and a residential development at Half Tide Dock.
Steve Mallinson has been the Contract Manager for all these Liverpool projects and he explained:
“We are now very used to the ground profile of the Liverpool waterfront which mainly comes from the amount of trial piles and different rigs and equipment we used at the Kings Waterfront development. This has stood us in good stead for the projects that followed.
The ground profile at Mann Island is no different, and we were especially confident of this when we conducted the piling works for the Museum of Liverpool – a project next to the Mann Island Mixed Use development.”
For the project, Bachy Soletanche constructed a firm/hard secant piled wall and bearing piles which was split into two main sections. The secant was constructed from November until the end of February and was then excavated ready for the bearing pile works to begin in April.
The secant piled wall comprises 604 750mm diameter Continuous Flight Auger (CFA) piles, which covers the perimeter of the site to create a 363 linear metre secant piled wall. Due to the ground conditions on site, which has naturally high water content, the secant wall is Firm/Hard. To construct a Firm/Hard secant wall structure – and to make the wall as watertight as possible – Bachy Soletanche is using ‘firm’ or weaker concrete in conjunction with reinforced concrete piles.
To construct the secant wall, the female piles are installed first through a guide wall. These are cast with the firm concrete and drilled right down to the sandstone and left for two or three days to set. The male piles then bite into the female piles to make a solid wall structure.
It is the male piles which hold the weight of the structure and therefore steel reinforcement is incorporated into the full length of these piles. The male piles are constructed to depths between 11m and 14m and the female piles go to depths ranging from 7.5m to 14m.
With the male and female piles installed, the wall is then capped by breaking the tops off the piles and casting a capping beam – a reinforced concrete beam which links all the individual piles together.
Steve Mallinson continued:
“We did face a few challenges on site. In the design process we discovered that an old dock wall ran across part of the site. We knew we would eventually have to drill through the wall, but this actually proved quite straightforward due to the heavy-duty rig we utilised.
Also, when we began to construct the guide wall trench we discovered a shaft leading to the Queensway tunnel which provided ventilation during its original construction. The shaft is backfilled, but also falls directly in line with the secant wall. At this point we changed the design so that the pile line moved to go around the shaft wall.”
Although Bachy Soletanche faced these challenges, the ground engineering firm completed the first section well within its time specification. Throughout April, Bachy Soletanche was back on site to work within the secant wall excavation 6m below existing ground. This was part of the second stage of the project where Bachy Soletanche constructed 191 750mm bearing piles to carry the super structure. This part of the project completed at the end of April.