As part of a major strengthening programme on the London Underground, an innovative solution was required to provide long term strengthening to over 90 cast iron beams.

Following an extensive design and specification process, the result is the UK’s largest ever application of ultra high modulus composite reinforcement, supplied by global building product manufacturer Sika and national specialist contractor, CRL (Concrete Repairs LTD).

Covered Ways CW17 and CW20 are on either side of Embankment Station on the District line, built in the 19th Century using “cut and cover” techniques. The covered ways carry the weight of Embankment Gardens situated above the District line tracks. Although the cast iron beams were assessed and found to be adequate to support the intended loadings and in a good serviceable condition, there was serious concern that the cast iron beams could be overstressed, under unforeseen overloading.

The solution to the challenge lay with Sika CarboDur UHM and a well planned application procedure. An Ultra High Modulus Carbon Fibre Reinforced Polymer (CFRP) system, Sika CarboDur UHM is designed for high performance and demanding reinforcement applications.

The plates, measuring 7.3m long, 200mm wide (2no per beam) and maximum 4.7mm thick and offering exceptional reinforcing capability, proved the ideal solution. With over 1,300mtr of Sika Carbodur UHM plates applied, it has marked the UK’s largest ever project to use ultra high modulus composite.

Olu Ogunwale, Contracts Manager at Concrete Repairs, said:"The Sika solution proved the most practical method to strengthen the beams. With severely restricted access, in terms of both space available and the four hour window in which we could work, its ease of application – combined with a carefully managed schedule – enabled the project to be delivered within the allotted timeframe".