project: Drewstead Bridge Corrosion Control

client: TFL (FM Conway)
location: London
duration: 8 months
value: £700,000

scope of works:

Concrete repairs to the columns and crosshead beams
Supply and installation of a cathodic protection system

“The success of the project lay primarily in the collaborative working between London Borough of Lambeth, CRL, FM Conway and Free4m to establish a methodology which substantially mitigated the risk of working in a highly controlled and restrictive environment, enabling the refurbishment works to be completed in 4½ months without incident, within budget and to programme.”

Tony Parasram
Director
Free4M Consulting

Drewstead Road Bridge in Streatham Hill, London Borough of Lambeth, carries the B221 across the main railway line just west of Streatham Hill Station. It is a significant transport route for Lambeth with bus routes, commuting pedestrians, heavy goods and light vehicles constantly crossing the bridge. The current bridge, which was built in 1968 comprises of precast, prestressed concrete bridge beams spanning across the railway lines supported by two sets of four circular columns and a crosshead beam. In 2012 after a thorough investigation and testing of the bridge structure it became evident that repairs to the superstructure and the supporting columns and crosshead beams were required. After extensive planning and organisation of Network Rail possessions, in 2014 the bridge underwent a large-scale refurbishment to extend the life of the structure by at least another 25 years.

In December 2012 CRL Surveys were commissioned to carry out a limited programme of testing works to the supporting structure of the bridge. The survey consisted of hammer testing and making safe, cover meter surveys to selected areas, screening for chlorides and checking for depth of carbonation. A number of options were presented to the client outlining varying costs and benefits, and the final option ultimately agreed on consisted of a combination of concrete repairs with an impressed current cathodic protection (ICCP) system to the portal crossheads.

Detail design followed with the final works methodology developed through close collaboration between CRL, FM Conway and Free4m. It was agreed that all works within the railway corridor were achievable within a fully enclosed hoarding situated at railway platform level, thus establishing a ‘green zone’ and effectively removing all risk associated with engineering hours working, cancelled possessions, etc. The fully enclosed hoarding also ensured that as the works could be carried out over the winter months of 2014 with the station remaining fully operational throughout the project.

The refurbishment and repair of the Drewstead Road Bridge, over an operational mainline railway station, within a residential community and on a main trunk route was, in the main part, a conventional and run of the mill repair project for CRL.