The Kyogoku Power Plant is a pure pumped storage hydroelectric plant with a maximum output of 600 MW and is currently under construction by Hokkaido Electric Power Co., Inc. The tailraice tunnel connecting the surge tank to the lower regulating pond is approximately 2.5 km long and has an inner diameter of 6.4 meters. It is designed to allow the support of the internal water pressure (maximum: 0.95N/mm2) by the secondary lining and the ground.
As the design of the secondary lining must take into account the fact that the stress acting on the lining differs according to differences of the ground strength, evaluation of the material values of ground rock mass along the entire tunnel route is necessary.
This paper reports on the newly devised method of determining the rock class-based material values of rocks based on the results of both in-situ ground tests conducted prior to the design of the secondary lining and spot in-site tests repeated every meter along the tunnel route.