2022 Volume 32 Issue 2 Pages 153-164
In a discharge tunnel of Amagase dam redevelopment project, a stilling basin section is an extremely large cross-sectional tailrace tunnel to still a high pressure and large capacity of discharged water from the main gate. Bench cut method with pilot side and central drifts is applied, because tunnel passes through a fragile fracture zone intervening in solid sandstone and mudstone with small overburden. And observational construction method is applied during tunnel excavation. Soon after construction started, it was found that fracture zone was wider than expected during side drift excavation. Thus, RC pillar support, more effective side wall stabilization effects than initial plan, is developed. This paper reports a design, construction and observational construction on the first Japanese stilling basin constructed in the form of extremely large cross-sectional tunnel.
