The 2026 Geotechnical Engineering Proceedings Lecture: Strains in sprayed concrete tunnel linings at Heathrow Terminal 4 and back-calculation of stress

Overview

The Geotechnical Engineering Proceedings Lecture is a biennial lecture nominated by the Editorial Panel of ICE Proceedings Geotechnical Engineering.

This year's Lecture offers a rare opportunity to explore nearly 20 years of monitoring data from Heathrow Terminal 4 station, providing valuable insights into the long-term performance of sprayed concrete tunnel linings and the factors that influence their behaviour over time.

This paper describes the installation and interpretation of strain gauges embedded in the sprayed concrete lining of the concourse tunnel at Heathrow Terminal 4 station, with readings taken over nearly 20 years.

The rate of flow method was used to back-calculate stresses from the measured strains, which were then compared with the stresses obtained from pressure cells at the same locations.

The resulting 20-year history of stress and strain gives precious insights into the short- and long-term behaviour of a sprayed concrete lining.

An increase in compressive strain up to 3 years followed by a slight decrease over the subsequent 15–16 years has been revealed.

It is hypothesised that this is due to radial groundwater flow through the primary lining followed by the gradual application of hydrostatic water pressure to the waterproof membrane and secondary lining.

Programme