Information and Communications Technology for the Construction of Underground Powerhouse Cavern in the Kyogoku Hydropower Project

This paper presents the outline of observational construction scheme employed for underground cavern construction, and of the Information and Communications Technology (ICT) as a technological tool to facilitate the observational construction. The Hokkaido Electric Power Co., Inc. has been conducting a Hydropower Project in Kyogoku, on the Pepenai and Bihinai tributaries of the Shiribetsu River in Hokkaido, Japan. The Kyogoku Hydropower Plant is the first pumped-storage hydroelectric power plant constructed by the Hokkaido Electric Power Co., Inc. It will output a maximum power of 600 MW, with an effective head of 369 m and a maximum water usage rate of 190.5 m³/s. The power plant is housed in a large underground cavern of which the dimension is 45.8 m high, 24.0 m wide, and 141.0 m long. Its total excavated volume is 116,000 m3 and the maximum cross-sectional area amounts to 1000 m². The geology of the construction site belongs to a so-called "Green Tuff" region of the Miocene period, primarily composed of tuff breccia. The geological condition presents considerable challenges, including a distribution of tuff blocks and two major fault zones with a low uniaxial compressive strength, presumably due to faulting and hydrothermal alteration. Therefore, observational construction method was applied to the project in conjunction with other ICT-solutions, and the actual rock response during excavation was examined in order to ensure the optimum structural support for the cavern as well as construction safety.