THE SCHEME
Bachy Soletanche continued their involvement with the prestigious, Wimbledon All England Lawn Tennis Club, when they delivered the geotechnical package for the latest phase of the club’s redevelopment. Bachy Soletanche were contracted by Sir Robert Alpine undertake the extensive piling and foundations work which involved the redevelopment of Court 19 along with the surrounding area with an extension of the existing basement and top-down construction of the plaza area.
CONSTRUCTION AND DELIVERY
Piling involved the installation of 102 No. 450mm diameter tension piles, 17.1m in length, from the existing ground level to overcome heave following excavation; 21 No. 1050mm diameter and 30 No. 1200mm diameter piles, 7.65m in length, to form the contiguous bored pile retaining wall for the extension of the basement; and 15 No. 1200mm diameter piles with plunge columns, ranging from 17m to 26m in length, to facilitate the top-down construction. All piles were installed using a Rotary Bored technique, with 4.5m thin-walled temporary casing.
The piling was undertaken with two different sized rigs to accommodate the split in pile sizes. The R312 was used for all of the 450mm diameter tension piles; then the company’s new LB24 was mobilised for the larger diameter piles and the deep plunge column piles.
The 15 plunge columns required for the top-down construction were supplied with a debonding agent and cast into piles with a cut-off level 5m below the piling platform level. The plunge columns were installed to great accuracy using Bachy Soletanche’s laser-levelled plunge column frames. The frames ensured that the columns achieved a positional tolerance less than 10mm, in-plan rotation of less than 20, and a vertical tolerance greater than 1:300.
The site was very restricted due to the small size of the piling platform, the installation of the plunge columns and the limited laydown areas available. This required the site team to work efficiently whilst sequencing both the plunge columns and the contiguous wall piles. In addition to this, a ‘just-in-time’ ordering strategy was adopted for material deliveries to site in order to maximise the available space.
Further efficiency was achieved using the RCL Super-Latch cage splicing system which was fitted to the plunge column cages fabricated by Total Construction Supplies. The system allowed the site team to connect two 12m cages with 4m of overlap in a matter of seconds as the cages were lowered into the open bore. The system also allowed for a huge leap forward in operator safety, as the system removes the need for hands to be placed inside the cages.
Throughout the project our team remained entirely self-sufficient by providing and managing all the required attendances. The crane was supplied in the form of a 60 Tonne tracked mobile crane, again to maximise the use of the small working area. A 13 Tonne excavator was chosen to be sufficiently powerful for all operations without occupying more room than was necessary on the platform. The excavator had to be capable of loading 8 wheeled tipper wagons for the purposes of removing the spoil from the site, a task also organised and managed in-house. The setting out of pile positions and recording of as-build pile positions attendance was provided Simplex Westpile too.
The concrete supplied for the project was beyond the specification of the project tender, in order to meet the company’s strict requirements on concrete quality in the finished piles. As part of these requirements pre-contractual concrete trials were conducted, including the casting and testing of concrete cubes. Once the mix design had been verified, the site team conducted rigorous on site testing of the fresh concrete to monitor the quality of material and ensure it was compliant.
Bachy Soletanche successfully completed the works within the scheduled 5 week period. This was an extremely short duration for the extensive piling works conducted and hugely beneficial for Sir Robert McAlpine with their critical timeline for handover for the 2017 Championships.
