For some structures, extended maintenance is a viable option and prolonging the service life of PC44 was commissioned by LUL. This project was delivered on time and budget by LUL and their contractor Clancy Docwra/Concrete Repair JV, culminating in the strengthening of the cast iron bridges using innovative Sika Carbodur UHM carbon fibre plates.

The end product is a structure with an extended design life that reduces expensive and dangerous cyclical inspections and represents excellent value for money for the client and taxpayer. Not only did the chosen delivery method cause no disruption to the underground system, but there was only minimal disruption to the road users.

However, getting to workable solution for this structure with its complex access and environmental conditions was far from simple. PC44 is one of the most technically demanding structural strengthening projects ever carried out using UHM Carbon Fibre Plates applied to a cast iron structure.

Pipe Crossing PC44 is an underline bridge supporting the District & Circle line tracks between Blackfriars and Temple Stations and over the fleet sewer. The asset was constructed in 1886.

The cast iron troughs that support the tracks and form the roof slab gave cause for concern in that they could fail without warning. Carbon fibre plates were bonded to the soffit of these troughs to provide an additional reserve of strength that will remove this concern.

Understanding the challenges presented by the sewer environment below this asset lead LUL to work closely with leading specialist in the field of structural strengthening and to commission significant independent testing and research, to ensure that the highest level of performance was achieved by using the right structural adhesive for the project in the very challenging conditions. Trials were also carried out to ensure the installation method was achievable. Well done to all involved in PC44 and achieving a commendation in the ICE London Civil Engineering Awards 2014.