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Brompton Road

The Brompton Road project required new foundations, and an extended basement for a retail and residential building. The site had an existing basement over part of its footprint and was fronted by the busy Brompton Road, opposite the Harrods store. The site was also bounded on two sides by existing buildings and the rear access was restricted in both height and weight.

The design required bearing piles to be 900mm diameter and to extend 36.5 metres below the existing basement level; also the existing basement was to be deepened by a new contiguous bored pile wall 600mm diameter and 12 metre deep. The ground conditions required the installation of temporary casings up to 10 metres long to seal off water-bearing sand and gravels above the London clay.

The small plan area of the MP5000 and MP4000 rigs allowed both machines to be working at the same time on the project, thereby reducing the programme period, and the light weight and small size of these machines enabled access into the site which would have been unavailable for bigger machines.

Cannon Place

The Cannon Place redevelopment in London required additional foundations to support the new loads imposed by the redevelopment scheme. Martello Piling, were employed to install 750mm diameter piles inside an existing basement of the existing structure.

In order for access to be gained to the basement some of the existing floors were cut to allow Martello’s MP4000 series rig to be lifted in by tower crane and lowered to the basement floor.

Martello Piling installed 750mm diameter piles in between the existing large diameter under-reamed piles, the new piles were installed to a depth of 36m, with the rig working in the existing basement only 3.6m high.

Cannon Street Station

The redevelopment of Cannon Street station involves the demolition of a 1960’s office building and the innovative re-use of some of the existing foundations. The existing foundations consisted of hand dug caissons 2.1 metres diameter with 6 metre square hand dug pyramid shaped under-reams. The designers required settlement reducing piles to be installed to very tight tolerances between the under-reamed bases. The piles required were 750mm diameter and 36 metres deep.

The restrictions of the site required the use of the MP4000 rig working in headroom of just 3.5 metres and the lifting in of an MP5000 rig to work in areas with no headroom restriction.

The rig lift was carried out by one of the on site tower cranes. Due to the crane’s capacity the rig lift weight had to be reduced and this was done by removing the rotary head and main winch and re-fitting these again on site. The Martello fleet of rigs all have designed lifting points and these together with the in-house design capability to re-calculate the balance of the rigs following the component removal enabled a safe lift to be carried out.

During the course of the work it was found that the under-ream bases were skewed somewhat compared to their theoretical position and this required the coring of the bases and on occasions the installation of up to 18 metres of temporary casing to seal off ground water which had tracked down from the water bearing sands and gravels to the base of the under-reams. The temporary casing was successfully installed to this depth, enabling dry boring and concreting operations to be carried out. Martello’s own design casing extractors were then able to remove the temporary casing. Coring of the under-ream bases at 18m depth was carried out using a combination of tungsten carbide tipped core barrels and temporary casing with tungsten carbide tipped cutting shoes.

The MP4000 rig also required lifting in and this was achieved with just 200mm clearance from the 2.3 metre width of the rig.