Sprayed Concrete Lining Falls and Exclusion Zone Management

Like most major urban centres, London is faced with an ever increasing population and the need to transport people to their places of employment and entertainment. The Crossrail project provides an East-West link from the suburbs to the city enabling an additional 200 million journeys each year linking up major business centres and existing transportation interchanges, while reducing congestion at street level and within the current over-used underground system.

In the central section of the project, in addition to over 42 km of precast concrete lined bored tunnels the project has constructed major structures in Sprayed Concrete Linings (SCL), including 5 new stations, 6 crossover caverns and numerous passages, adits and ventilation tunnels. The construction of these structures has taken approximately 4 years, and has involved the spraying of over 200,000 m³ of concrete, a small proportion of which fell from its designated location when applied. The safety implications of falls of SCL was a major concern from the start of the project, but it was evident that a complete lack of available records from previous projects hindered risk assessments or the ability to make meaningful comparisons concerning spraying or material performance. This paper therefore attempts to redress this lack of data by providing information on the falls experienced on this project, allowing frequency and volumes of falls to be judged, and providing guidance on the efforts made by the project to reduce falls further even though exclusion zones to high risk areas were imposed.