Olympia Redevelopment

Planning for this phase of works began a full 12 months before mobilisation due to the challenging access and working constraints. The overall concept of the building is for construction of additional storeys above the current building with the new steel frame structure threaded through the existing floorplates and supported by a steel frame founded at basement level on pilecaps. The piling scope was designed and installed in two distinct phases comprising;

• Phase 1 in Spring 2021– 300mm bearing piles installed at basement level within the confines of the existing structure
• Phase 2 in Summer 2021 – 600mm piles for the core structure also installed from existing basement level

These works were managed by the site-based project team concurrent with ongoing piling works across other areas of the Olympia Redevelopment each with their own delivery as well as specific technique and logistical challenges.

Because the piling works wer e undertaken concurrent with the Olympia events programme this required the development of a sympathetic logistics strategy which eliminated impact on the running of the shows.

Prior to mobilising any rigs to site, a detailed 3D model of the site was created supported by extensive site surveys to plan the rig working positions and access routes to each pile location checking that a safe working envelope could be provided and where this wasn’t available developing a strategy to mitigate this by a number of means including repositioning piles in coordination with the engineer.

This digital build allowed the piles to be ‘installed’ a number of times before an auger touched the ground onsite meaning potential issues around accessibility could be identified, a solution agreed collectively and fed back to the design team or implemented by the site team in the case of additional service diversions or extra soft strip by the demolition contractor.

The basement piles were designed as 300mm diameter and installed using SuperKitten mini rigs with up to two rigs working concurrently in a sequence developed with the preceding demolition sub-contractor and follow-on sub-structure works to allow the earliest start for steelwork erection accounting for the phased handover of the work areas from the client. SuperKitten rigs were selected as all the piles were installed from the existing basement slab which meant that headroom was limited to 2.7m.

Access to the working areas at basement level was extremely limited with no direct vehicle route or crane access. Both rigs, powerpacks and attendant plant were mobilised to site using the existing site service lifts after having been reduced down to a weight and size that could be accommodated.

In addition to the logistics, pile locations were extremely close to and in certain places directly underneath the live show spaces which required the team to development a robust noise mitigation strategy to ensure that construction activities did not impact the concurrent events. This included bespoke noise shrouding of power packs, employing electric attendance plant and sequencing deliveries outside of event operating hours.

All the basement piles were grouted using site batched grout from a pump station set up within a pitlane that allowed events traffic and deliveries associated with other construction activities to continue without impact.

The permanent works piles for the core plus the temporary piles for the tower crane base were all designed as 600mm diameter and installed using a case & auger technique using a KR709 mini piling rig. Whilst the main area of the core piling had no headroom restrictions, the space for rigging up meant that a mini piling rig was selected. In addition the complex temporary works associated with cutting the core opening through the existing building whilst retaining the surrounding structure meant that a number of piles were installed with a headroom limit of 4.5m which necessitated mobilising the rig with a bespoke low headroom mast.

During the design phase, Expanded worked with Robert Bird Group to value engineer the scheme by;

• Reducing the number of piles – this provided cost and programme savings as well as a saving in the embodied carbon by leveraging the experience of the specialist geotechnical design team within Expanded
• Rationalise to a single pile diameter – this allowed all the piles to be installed with a single rig type omitting the requirement to mobilise larger rigs which would require additional demolition of the existing of the existing structure plus increased disruption to the client events during mobilisation/demobilisation phases
• Redesign the pile reinforcement to reduce the overall cage length – this allowed the cage length to be reduced by 70% saving on the number of pile cage sections required

Whilst the construction of the core structure necessitated removal of the central area of the existing structure, there was only pedestrian access down to the piling platform level for the core piles. The team reviewed a number of options for delivery strategy of the core piles including forming temporary ramps for access and reducing pile diameters, but the selected option was to lift the equipment over the retained structure and down the basement level by mobile crane presented the least disruptive solution for the Olympia events programme.

Because of the value engineering that was accomplished during the design phase, the number of cage sections required for the core piles was significantly reduced. This meant that all the cage sections could be delivered to site at the start of the works and lifted in as part of the rig lift operation thus allowing the crane that had been planned to be required for the duration of the works for lifting cages into the core ‘just in time’ to be removed which offered a cost saving but also freed up the area where the crane would have been positioned for other concurrent works to commence early.

Along with the piling rig, all the associated tooling, attendant plant and pile reinforcement cage sections were also lifted in as a two-day crane operation using a 130T mobile crane planned and managed by the Expanded site team with support from the specialist lifting department within Select Plant.

Because of the pile cap depth below the working platform level the Expanded team introduced the Recépieux system to simplify the breaking down of the piles to cut off level. This system is a novel method not widely used in the UK of cutting down piles eliminating the use of hand breakers and thus an improvement in HAVS plus a quicker method of preparing pile heads ready for the pile cap construction.

Full scope of works:

• Setting out
• Geotechnical permanent works design
• Temporary works design in support of piling including working platform design and temporary bracing for mobile crane lifts
• Scoping of demolition and enabling works delivered by sub-contractor
• Attendances to piling works including muckaway and temporary ventilation
• Pile probing & obstruction removal
• 600mm bearing piles up to 27m depth in 4.5m headroom
• 300mm bearing piles up to 15m depth in 2.7m headroom
• Integrity testing of bearing piles using sonic echo techniques