CIVIL ENGINEERING CATEGORY
The 365m-long Thames Tunnel linking Wapping and Rotherhithe stations on London Underground’s East London Line is of immense historic interest as the world’s first significant sub-aqueous tunnel. Constructed by Sir Marc Brunel between 1825 and 1843 with his more famous son, Isambard Kingdom Brunel, working as resident engineer during the early part of the tunnel’s construction, the tunnel was in urgent need of strengthening.
Suspension of the contract caused by the tunnels being given a Grade II listing meant that the original solution of forming a new 200mm-thick sprayed-concrete internal lining reinforced with fibre and mesh was revised. Instead, a more complex solution was adopted consisting of a minimum 200mm- thick in-situ and sprayed-concrete shell with 56 interconnecting cross- passages each incorporating architectural features as originally constructed by Brunel. The scheme also retained 30m of the original tunnel under the south bank of the Thames. This more complex tunnel profile led to a general change from a sprayed to a formed concrete lining, and an extensive ‘behind- lining’ drainage system was provided.
All the concrete - some 4000m3 - was site batched. Microsilica was incorporated to improve durability, finish, cohesion and pumpability. It also eliminated the need for saline application. The difficulties with the sprayed lining were exacerbated by the design requirement for two layers of reinforcement/ mesh in addition to the fibre reinforcement retained for blast resistance. The solution was to spray against ‘Expamet’ to the required minimum thickness and later fill the resulting void behind the sprayed-concrete lining with grout.
Four hydraulically operated steel shutters were used for the tunnel lining. Concrete was placed by pump and compacted using external vibrators. To enhance shutter efficiency and minimise the programme, concrete temperatures were recorded and cubes matched-cured and tested so that the shutters could be struck as soon as the concrete reached 18N/mm2.
This project is a success story that provided a value-for-money product, preserved and enhanced the heritage, encouraged economic regeneration and was delivered ahead of programme and within budget.
OWNER London Underground
EMPLOYER’S AGENT W S Atkins Rail
CONSULTING ENGINEER Dr Sauer Co.
MAIN CONTRACTOR Taylor Woodrow Construction
PORTLAND CEMENT Blue Circle Cement
FORMWORK Expamet Building Products