Northeast Boundary tunnel (NEBT) is part of an extensive project promoted by DC Water aimed to reduce the frequency and magnitude of sewer flooding in the city of Washington. With a geology characterized by a stratigraphic sequence formed by fill, alluvium deposits of soft-clay and Potomac deposit soils, the tunnel 8.23km long is being excavated with a 7.8m diameter EPB.
The running tunnels were designed as SFRC (Steel Fibres Reinforced Concrete) by Tunnelconsult and conventional steel reinforcement were also verified to be installed within the segments at shaft and adit connections.
The Torito HEP project is located in the Reventazón river catchment, downstream the Angostura
hydroelectric. The installed power is 50 MW and the average annual production 305 GWh. The tunnel has a length of 3.5 km and has been excavated using an EPB TBM (Earth Pressure Balance
machine). The ground overburden ranges from 35 to 180 m. The geology of the tunnel mainly consists on calcarenites, conglomerates and pelites, and a short stretch of soil deposits. Nine faults are identified along the tunnel alignment.
Tunnelconsult provided technical assistance to the Client in the segmental lining revision and supervised the headrace tunnel excavation.
Tunnelconsult assessed the fiber manufacturer on the applicability of SFRC to the segmental lining to be adopted for a test ride in Xili tunnel (Shenzhen Metro). The 5+1 segmental lining ring with an inner diameter of 5.4m and 300mm of thickness was standardly reinforced with 148 kg/m3 of rebars. The segmental lining optimisation carried out by Tunnelconsult resulted in 45 kg/m3 of steel fibers with a light perimeter cage to be installed in the test stretch. Apart from the design, Tunnelconsult also assessed segments production, validation testing and installation.