December 8, 2015: Owner design of the 11.25km x 5.5m i.d. Los Angeles effluent outfall tunnel in California, USA, is reaching an advanced stage of completion ahead of design-bid-build construction procurement next year (2016).

The new infrastructure is being built to replace two smaller tunnels of 12ft and 8ft diameter that connect the inland wastewater plant in Carson City with ocean outfall structures at Royal Palms Beach.

Access to the original tunnels, which already flow to full capacity and are not sufficient to meet Los Angeles Sanitation Districts’ future needs, has not been possible since they were constructed in 1937 and 1958. They will be inspected and rehabilitated as necessary once the new tunnel is completed, and held in reserve so that maintenance can be carried out on the new tunnel if necessary.

TBM excavation of the new tunnel, which is scheduled to take 54 months, is expected to start in 2018. The project will feature the first use in the USA of post tensioning (PT) of the segmental lining. Up to 40% of the alignment will feature PT in order to maintain integrity as a result of internal pressure during pumping out operations.

Snapshot

Los Angeles effluent outfall tunnel

Project:	Joint Water Pollution Control Plant (JWPCP) Effluent Outfall Tunnel
Owner:	Sanitation Districts of Los Angeles County (SDLAC), USA
Procurement:	Design-Bid-Build
Owner design:	Parsons Corporation McMillen Jacobs Associates
Geotechnical consultant:	Fugro Consultants
Expected cost:	US$550 million
Tunnel dimensions:	8 miles (11.25km) 18ft (5.5m) i.d.
Primary lining:	115-18in (300-375mm) pre-cast concrete segmental lining
TBM requirements:	Approx 21ft (6.4m) diameter EPBM or slurry machine
Shafts:	30.5m deep launch shaft No intermediate shafts
Design features:	Post tensioning of 40% of   concrete segmental lining Grout-backfilled steel pipe   through geological fault splays
Seismic considerations:	Alignment traverses the active Palos Verdes fault
Geology:	Alluvium (north) Rock-like material (south)
Interviewed:	David Haug, Project Engineer SDLAC