Excavation of a cavern for high-pressure storage of natural gas

During the last 20 years a new storage technology has been under development for the world market. The first lined rock cavern (LRC) for storage of gas under high-pressure, constructed at Skallen, in southwest Sweden is now complete. The project is a joint venture between Sydkraft of Sweden and Gaz de France for the development and demonstration of the LRC-Technology. The excavation work was completed at the end of 2000 and the construction work was finished 2002. After a test period of one and a half years, the facility has been in commercial operation as a part of the Swedish gas grid since early 2004. The main features of the below ground facility are a 1 km long access tunnel, a 115 m deep vertical shaft and a 40,000 m3 rock cavern. The cavern is designed as a silo, 52 m high and 36 m in diameter, with a large cupola and curved form bottom. The host rock in the area is crystalline gneiss of good quality, intersected by amphibolite dikes of poor quality. During construction, the stability of the cavern has been monitored by extensometers around the cavern and convergence measurements in the cupola. Only small deformations of a few millimeters have been recorded. This paper describes the cavern rock design and the experiences from the excavation works, along with a comparison of predicted and recorded deformations. A number of rock mechanic analyses have been carried out to determine rock stability and rock support.