Case Study

The Challenge

South Thames College is a new residential and commercial de-velopment consisting of four blocks. Three of these blocks share a single storey basement. The site is located within the one-way system of Wandsworth. Whilst access and working area was relatively unrestricted, the presence of a Thames Water Sewer at a shallow depth running through the centre of the site meant additional consideration in pile construction was required.

In addition, the secant piled wall which follows the line of the sewer on one elevation was located in close proximity to the ‘pile exclusion zone’ set by the service provider.

Relic piles and old concrete foundations were left in the ground where it was not viable to remove. This meant the secant wall, which, by its nature must form an interlock, would need to be installed taking in to account positional restrictions of the sewer and requirements to not deviate the piled wall in to the basement footprint if obstructions were encountered.

The client required an engineered solution which considered the formation of the secant basement whilst ensuring relic piles did not hinder the secant wall and to make certain the sensitive Thames Water infrastructure was not compromised.

The Solution

Our in-house design team designed a 750mm diameter secant bored piled wall, installed using the CFA technique with our Soilmec SF-65. To deal with the relic piles and obstructions in the line of the wall we mobilised our Bauer BG-20 bored piling rig to site to core out the obstructed positions utilising rotary coring methods.

A return visit in July allowed all remaining 750mm dia. bearing piles could be installed from a reduced level within the basement footprint straight in to the London Clay. In turn this meant rotary bored piles could be utilised to achieve the high working loads in on 750mm diameter piles installed to a depth of 28.5m.

Savings were made as a result of:

Decreasing pile diameters from 900mm, as originally de-tailed, to 750mm as proposed by Franki design team.

Piling at a reduced level where London Clay was present meant reduction in concrete quantity and reinforcement as piles would have otherwise been constructed from ground level. The higher platform level would have meant CFA piles or temporary casings to depth would be needed as a consequence (due to presence of granular drift deposits).

Even though significant additional relic piles and obstruc-tions were encountered Franki still delivered the scheme within budget and to the original proposed programme.

The Project Residential

Completion Date August 2017

Value £956,000.00