Lord Hill’s Bridge Mitigation Works

Summary

Lord Hill’s Bridge (LHB) was the first piece of infrastructure that the Western tunnels TBM’s passed beneath, at a depth no greater than 4 m below current ground level. The shallow tunnelling depths are a result of the 100 year old bridge being located 50 m east of the Royal Oak Portal head wall. The bridge itself is a simply supported two span structure passing over the existing Network Rail (NR) main lines, London Underground (LU) Hammersmith & City tube lines and the proposed Crossrail Western tunnels. Royal Oak tube station entrance is positioned at the central pier of the bridge and 3 utilities span the bridge deck in the form of: 1 x 600 mm gas main, 2 x 450 mm water main and 2 x 66KV power cables. Assessments undertaken in recent years highlighted that the bridge was in a poor condition, the latest report in 2005 recommending that the bridge be re-built in the next 4 years due to the deterioration of the structure. A combination of the condition of the bridge and the shallow tunnelling depths led to the implementation of programme critical mitigation works. A design for ground replacement below the bridge was developed; this involved the installation of vertical piles beneath the bridge and raking piles beneath the north abutment of the bridge. In total 1225 piles up to 15m in length were to be placed below the bridge with a working headroom of 5.0 m. Upon the bridge deck diversions of the water main and gas main were undertaken while the 66Kv cable chamber was exposed to allow for monitoring installations. All works were carried out whilst the bridge deck was live to traffic and pedestrians, as well as the adjacent Network Rail and London Underground transport services beneath the bridge.