Channel Tunnel Rail Link Contract 320 Thames Crossing

Description of Works

These works were undertaken in a joint venture with Hochtief AG. This consisted of a 50/50 fully integrated joint venture between the two companies. The works comprise the construction of 3.6km of the CTRL route between Swanscombe in Kent and Thurrock in Essex

The principal elements of the works included:

The Thames Bored Tunnels, which comprised 2.5 km long, twin 7.85 id, 7.15 id bores under the River Thames. The tunnels were driven with a closed face slurry Mixshield TBM supplied by Herrenknecht, and constructed using bolted precast concrete segmental tapered linings reinforced with steel and polypropylene fibres. The segments were cast on site in a purpose built factory at the Swanscombe site. The tunnel drive was principally through weathered chalk with approximately 350m at the start and finish of the drives being through alluvium, peat and gravel. Both drives commenced at the Swanscombe portal.

The contractor was responsible for the design and supply of the Mixshield TBM and its slurry removal and processing system. The TBM included an air lock system, stone crusher, grout injection tubes, and the system was designed to operate with a water head of up to 4.5 bar.

The Project also included the construction of the Approach Structures on the Northern and Southern side of the River Thames. The Northern Approach Structure comprised 100m of retained cut and 300m of cut and cover box, with central dividing walls, and was constructed using diaphragm walling and bored piles. The Southern Approach Structure, also used as the TBM launch chamber, comprised 450m of retained cut and 300m of cut and cover box with central dividing walls, and was formed by diaphragm walling and bored piles.

The ancillary works included tunnel cross-passages, track bed concrete, drainage system, fire main, evacuation walkways and ventilation shafts. Various buildings were required to house ventilation equipment and other ancillary electrical equipment.

Extensive site clearance and demolition of factory units was required at Swanscombe and Thurrock. Various diversionary road works and utility diversions were included in order to allow construction of the works.

The contractor was responsible for all planning, obtaining consents, licences and traffic orders necessary for the contract. The environmental sensitivity of the work sites necessitated that a detailed environmental plan was in place. Close liaison with the Environment Agency and Local Authorities was essential.