Los Angeles moves Clearwater into final design
25 Jul 2013
Peter Kenyon, TunnelTalk
- Parsons is selected to implement final design of a new US$550 million TBM-bored outfall tunnel in Carson, California.
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Onshore 11km alignment selected
- The 11km (6.9 mile) x 5.5m (18ft) i.d tunnel, which forms part of the Sanitation Districts of Los Angeles County Clearwater Project, will convey treated wastewater from an upgraded treatment plant in Carson to an existing network of four sea outfalls (Fig 1).
- Construction of the new tunnel will add critical capacity to two existing tunnels of 2.4m (8ft) diameter and 3.7m (12ft) diameter that were constructed in 1937 and 1958. As part of the project these two existing effluent tunnels, which flow at full capacity every day, will be dewatered and inspected for the first time in 50 years.
- The alignment of both the existing tunnels and the new one crosses the active Palos Verdes fault.
- "Parsons performed the feasibility analysis and preliminary engineering for this project, and we're pleased to have been selected for this next phase of the tunnel,"said Virginia Grebbien, Parsons Group President.
- Project scope calls for construction of a 42.7m (140ft) deep x 12.2m-18.3m (40ft-60ft) diameter launch shaft at the existing treatment plant, an intermediate shaft, and a 15.2m (50ft) deep x 7.6m-10.7m (25ft-35ft) diameter reception shaft at Royal Palms on the coast. EPBM or slurry TBM is selected as the excavation method on account of the highly urbanized nature of the alignment.
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Four tunnel options considered
- The tunnel would be constructed of pre-fabricated, steel reinforced, concrete liner segments with watertight gaskets.
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During a feasibility study four alternatives were investigated (Fig 2):
• Option 1 - 20km offshore and 3.2km onshore tunnel
(total length 23.2km). Estimated construction cost
$1.36 billion, estimated completion time 8 years.
• Option 2 - 11.6km offshore and 3.2km onshore tunnel
(total length 14.8km). Estimated construction cost $980
million, estimated completion time 6.5 years.
• Option 3 - 3.5km offshore and 10.3km onshore tunnel
(total length 13.8km). Estimated construction cost $910
million, estimated completion time 6.5 years.
• Option 4 - 11km onshore tunnel to connect with existing
(and rehabilitated sea outfalls. Estimated construction
cost $550 million, estimated completion time 6.5 years. - It was concluded that Option 4 achieved all of the project goals at the lowest cost and with the fewest environmental impacts and with the least amount of construction risk.
- Design, bid and contract awards are scheduled to be complete by the end of 2014, with 12 months of shaft construction slated for 2015. Four years of tunneling (3Q 2016 - 3Q 2020) is anticipated, with construction bids expected in the $478 million region (2011 figures).
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