Takase Dam, Nanakura Dam and Omachi Dam are a system of barrages in the Northern Alps of Japan. Located in the northwest of Nagano prefecture, surrounded by 3000 Meters high mountains, they serve both as reservoirs for hydroelectric power stations and as flood protection dams. Large amounts of sediment flow into the Takase Dam upstream of the Takase River from the left tributaries (Muddy River and Fudozawa).
The purpose of the Omachi Dam Tunnel is to limit sedimentation and to maintain the flood control capacity and power generation capacity of the Takase Dam for the future. The plan is to construct a sediment transport tunnel (approx. 11 kilometers) between the upstream of Takase Dam and the downstream of Omachi Dam, as well as to establish conveyor systems, a sediment separation plant, and temporary sediment storage facilities.
In order to successfully overcome a number of geological challenges, including the probable presence of high rock strength and extremely abrasive rock Maeda Hazama Ando JV opted for a Herrenknecht Gripper TBM to excavate the sediment transfer tunnel. The Gripper TBM is equipped with various rock support measures such as rock bolting units, ring beam erector and shotcrete manipulator to also excavate through multiple fault zones and alteration zones affected by groundwater, shallow overburden with extremely weak rock and instability at face and surface. The tunnel spans 10.58 kilometers, climbs with a maximum gradient of 5,9 % and represents a crucial part of the Omachi dam upgrade. In addition, Herrenknecht subsidiaries TMS and H+E are delivering 6 Multi-Service Vehicles respectively tunnel belt conveyors. Herrenknecht Group member VMT provides a navigation system for TBM guidance during tunnel excavation.
This project will mark the construction of Japan's longest mechanized tunnelling with open mode in hard rock and become a notable achievement in the field of tunnelling engineering. Factory Acceptance took place in the beginning of 2024.
