Päijänne - world's longest tunnelReader Juha Huovilainen juha.huovilainen@marimils.fi has updated the tunnelbuilder Hall of Fame entry for Päijänne tunnel in Finland. After 27 years as the world's longest water supply tunnel, we are happy to upgrade the Päijänne tunnel to a new status as the world's longest continuous tunnel from point to point.The Päijänne tunnel is owned, maintained and operated by Helsinki Metropolitan Area Water Company. It is located in southern Finland, and the headquarters of the company are at Mannerheimintie 107, 00280 Helsinki, Finland. Visit www.psv-hrv.fi.The tunnel supplies raw water to the Helsinki area waterworks for more than 1,000,000 inhabitants. It is 120 km long, from Lake Päijänne to Silvola reservoir. Its cross section is mainly 16 sq m, and average depth is 40-90 m below ground level. In the tunnel there is a water power plant, which regulates the discharge to the tunnel and generates electricity. The discharge capacity at free fall is about 10 cu m/s. The water intake is nowadays about 3.3 cu m/s and annually about 100 million cu m.The tunnel was excavated in bedrock of the pre-Cambrian migmatite granites and gneisses zone of southern Finland. The excavation of the 24 access tunnels and the main tunnel started at the north end in November, 1973 and ended in Spring, 1982. Designed in the 1970s, at a time when there was little experience on construction of water tunnels, insufficient reinforcement was installed, resulting in later problems with falling rocks. Repair of the reinforcement in the northern part of the tunnel was undertaken in 2001, and in the southern part in 2008. Nowadays there are about 50,000 bolts and about 40 percent of the walls of the tunnel are shotcreted, which doubles the original reinforcement. Grouting has not been extensively used because leakage is not an issue when the tunnel is in use. 36/09.