London: Bromley South Central

DAWSON-WAM was contracted by McLaren Construction to design and construct a 12m deep secant basement for the new Bromley South Central mixed used development in the heart of Bromley.

In total over 360 linear metres of secant piles and 350 load bearing piles were installed with piles ranging in length up to 23m. The secant pile wall consisted of 900mm and 750mm diameter Hard Hard piles.

All piles were installed through 2.5m of made ground and demolition material, and were bored through loose sand and gravels and founded into the very dense sands. Piles were installed to with 200mm of the neighbouring Direct Line Group structures.

DAWSON-WAM used their Cased CFA System to complete this close proximity work with the added benefit of the system protecting the existing foundations from ‘flighting’ which is prevalent in loose sands .

The scheme involved working adjacent to a live Network Rail Line which was limited to very tight 5mm deflection limits and vibration restrictions.7

The project timescales were dominated the phasing and relocation of a public road which bisected the site, a large storm culvert and other extensive service diversions.

As part of the works DAWSON-WAM designed, installed and removed over 350 tonnes of temporary propping for the scheme. The props were installed over 2 levels with the longest prop installed being 59m in length and 900mm in diameter.

As part of the contract DAWSON-WAM installed over 100m of temporary sheet piles and further contiguous pile wall excavation supports for the tower crane bases.

The site was located within a busy business and residential area and required thorough logistical planning and management.