The Lee Tunnel project consists of a 7.2m diameter, 6.9km long tunnel, and five of the largest and deepest hydraulic shaft structures ever built in the UK.

By taking a holistic approach to design and construction methodology on this project the SlipStress™ concept was developed. This shaft lining system enabled 5000t of traditional rebar to be removed from the shaft linings (up to 43m diameter by 85m deep). Double slip forming methods virtually eliminated shrinkage cracking, and concrete placed under pressure in the annulus also ensured that linings did not suffer damaging tensile stresses during service.

These innovations significantly improved the water tightness of the shafts, increased speed of construction, and delivered a £5 million cost saving to our customer along with a 60 per cent reduction in embodied energy and a 35 per cent reduction in carbon.