CONTRACTS HAVE been signed for a $899M (£493M) extension to the Los Angeles Metro Gold Line.
Final approval of a federal funding package allowed confirmation of the £330M construction contract with Eastside LRT Constructors, a joint venture of Washington Group International, Obayashi Corporation and Shimmick Construction Corporation.
The project will extend the light rail system 9.6km east from Union Station in downtown Los Angeles. It includes tunnelling as well as stations, elevated structures, bridge upgrading and a cutand-cover section.
About 240m of cut and cover leads into the first underground station on the section.
'The earth pressure balance tunnel boring machinery will be launched from here on its 2.9km twin-bore route heading east, ' explained LA Metro deputy project manager Eli Choueiry.
He said the area is congested and where the tunnel passes under structures and utilities, compaction grouting will be used to avoid any damage.
The twin tunnels will be about 6.7m diameter, running mainly through alluvium with an escarpment section prone to deep underground movement. The tunnels are designed to accommodate seismic events, Choueiry added.
The precast concrete-lined tunnels will be done in a single pass with bolted, gasketed joints. Half of the tunnel alignment is above the groundwater table and the remainder below, though the same double-gasket lining is used throughout to provide tight joints.