THE SCHEME
Devonshire Park, with its rich history stretching back over 140 years, has long been an attraction within Eastbourne and the surrounding region. Home to a variety of leisure activities, the area has undergone several transformations, the latest being a £54m redevelopment, which will put Eastbourne on the map as a top cultural, sporting and conference destination.
The new Welcome Building will provide a fully accessible entrance to the Congress Theatre, two new large conference spaces, a central box office, hospitality areas and a coffee and wine bar with views across the tennis lawns to the International Tennis Centre.
PLANNING AND PRE-CONSTRUCTION
Bachy Soletanche were appointed by VINCI Construction UK to deliver the geotechnical package for the scheme. During the pre-construction phase it was evident that restricted nature of the site and the location of the adjacent properties would play a key role in determining sequencing and rig selection.
The secant piles positions were in close proximity to the Grade II listed buildings and in addition to this, an exclusion zone, applied by the International Lawn Tennis Centre, had to be adhered to. The team had to select a CFA rig that could still construct the required pile size and depth, without adversely affecting the buildings, or infringing on the exclusion zone.
Initial proposals included forming all the piles from a single piling platform level over the course of one visit. However, it soon became apparent that this approach would constrain the subsequent construction of the basement structure and therefore a two-phase programme was adopted. The secant pile wall was designed as a cantilever in the temporary condition, to enable unrestricted access for the bulk dig prior to the second phase of piling works.
PILING OPERATIONS
Phase one of the project saw the team construct a secant piled retaining wall and a small number bearing piles during a four-month visit. The wall, 255m in length with a maximum retained height of 4.2m, was formed using the following piles:
In addition to the wall, the team installed four 600mm diameter CFA piles, providing support for a tower crane base and three 450mm diameter CFA tension piles, all bored to a depth of 13m. During this first phase of works, the secant piles were sequenced in a way that allowed for a seven-day suspension of piling operations so not to impede on the prestigious Eastbourne International Tennis tournament.
Following the construction of the secant wall, the capping beam and bulk dig were undertaken by the main contractor and a piling mat was installed ready for phase two. The second visit saw the operation move to inside the basement and consisted of the installation of 87 CFA tension piles, with a diameter of 450mm and an average depth of 10m.
