References
Canary Wharf Heron Quay
UNITED KINGDOM, 1999-2000
Basement walls and bearing piles for a major commercial development.
Canary Wharf is located in the heart of the London Docklands, to the east of the city and has been undergoing regeneration since the mid-1980s.
Bachy Soletanche were awarded various contracts on the New Heron Quay (HQ) development. This comprised installing some 1100 piles over a 14 month period. The works comprised hard/ hard secant piling to form basement walls to buildings HQ5 and HQ1 , and Bearing Pile installation to the main Heron Quay Cofferdam, to form foundations for buildings HQ2 and HQ3.
Specially adapted rigs were utilised for lowhead wall operations, adjacent to the Docklands Light Railway System, which crosses the site.
Ground Profile
The general soil conditions underlying the site were fill, terrace gravels, Lambeth clays, Lambeth sands and gravels, and Thanet sands. Two water level conditions prevailed, the upper aquifer in the terrace gravels, and the lower in the Thanet sands. Unique to Canary Wharf was the artificially low water table in the Thanet sands, which reduced the ground water to beneath the pile-constructed bases. This allowed Bachy Soletanche to drill piles without the aid of drilling fluids. However, a requirement of the Performance Specification required pile boreds to be charged with a temporary support fluid prior to concreting, thus minimising the risk of pile collapse during concreting operations.
Construction Methods
• All piles at Heron Quay were constructed in the following manner:
• Install temporary casing (6-15m in length)
• Temporary casings to secant walls extended to 30m
• Drill pile to design depth
• Flood empty bore with bentonite support fluid
• Insert reinforcement cage (with reservation tubes already attached)
• Concrete pile
The day after pile construction the Tube a Manchettes (TaM) attached to the steel cages, would be opened and the pile base concrete cracked using water under pressure up to 20 bar. This then left the pile ready for base grouting operations a day later.
For base grouting, grout would be injected through the reservation tubes to the base of the pile in compliance with the Performance Specification requirement of minimum volume, pile uplift and residual pressure.
Special Requirements
On sections of the development it was a requirement for piles to be installed through old dock wall (mass brick and concrete).This was achieved only by utilising Bachy Soletanche's high torque piling rigs. The wall was cored using 1200mm and 900mm diameters to depths of 15m. All piles on the contract required base grouting to minimise settlements and enhance load - bearing capabilities. Working test piles were required to loads up to 30 Mega Newtons (3000 tons) using Bachy Soletanche's standard test assemblies.
In order to complete the installation of 1500mm diameter piles, within a 12m height restriction under the Docklands Light Railway, a standard rig was modified. Plant operated in agreed orientations to the line, with defined jib/mast fall zone areas!
Techniques
A pile is a structural element driven into the soil for transferring loads and prevent deformation. Its slenderness ratio is not limited.
Pile shafts can be uniform and rectilinear, telescopic and belled out.
Piles can be installed either separately or in groups. They can also form a retaining wall, a mixed curtain wall, contiguous piles, secant piles and composite curtain walls, such as Berlin walls and similar. Piles are also used as precast beams to be placed in the structure of the building they support.
A retaining shell is a slim shell structure used during vertical excavations. Unlike retaining walls, the weight of a retaining shell has little effect on its capacity to balance the pressures.
Ouvrages
Suitable foundations are required for all building and civil engineering structures to ensure that they perform within the settlement criteria established in the design of the structure. Special foundations are used where shallow footings do not provide adequate support for a structure.
Major urban excavations are one of the specialist activities of Soletanche Bachy. Such excavations are required for basements to buildings that are usually part of the foundations of the structure and also used for under-street car parks, cut and cover tunnels for roads, rail, metro and storm water tank...
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