River Supply Conduit Improvement Upper Reach Units 5 & 6
This project involved construction of a new water transmission pipeline to replace an existing pipeline constructed in the 1940’s. The new pipeline will transmit water from the North Hollywood Pump Station to the Headworks Spreading Grounds in North Hollywood, CA. The project was constructed by a joint venture consisting of W.A. Rasic Construction Company and SAK Construction, LLC. SAK’s scope of work included excavation of five individual tunnels along the overall pipeline alignment. The combined length of the five tunnels was 10,364 linear feet. SAK utilized a refurbished Lovat mixed face EPBM to excavate the tunnels to a diameter of 129 inches. Pre-fabricated, fiber reinforced concrete segments were assembled within the tail shield of the TBM to provide temporary ground support during excavation. The precast segment liner had an ID and OD of 108 inches and 123 inches, respectively. Contact grout was pumped behind the segment liner as the tunnel is excavated; this grout was batched on-site. Upon completed of tunnel excavation, cement mortar lined steel pipe with ID of 79 inches was installed and backfill grouted within the tunnels. 20 foot long joints of pipe were hauled into the tunnel with a custom built pipe carrier before being blocked and welded in place underground. The EPBM was launched and received from multiple shafts excavated along the alignment. Worksites were typically set up in the middle of busy urban streets which added to the complexity of this project. Significant traffic control efforts were required to divert traffic around these worksites. During tunnel excavation, surface and subsurface settlements along with mass muck accounting were closely scrutinized. Zero surface settlement was observed during excavation and subsurface settlements monitored 5 feet above the EPBM were typically measured in hundreds of an inch; well below contract limits.