Underground Construction - August 2021 - 20

Creative Construction Sequencing
Aids Light Rail Construction
The Los Angeles County Metropolitan
Transportation Authority - LA Metro
- is in the final stages of constructing
an underground light rail trunkline
that will allow riders to travel through
downtown LA with far fewer transfers
and more direct service. Known as the
Metro Regional Connector Transit
Project, it will connect three existing
light rail transit (LRT) systems, reducing
commute times by up to 20 minutes.
Regional Connector Constructors (RCC),
a joint venture of Skanska USA Civil West
California District Inc. in partnership with
Traylor Bros. Inc., was awarded the designbuild
contract by LA Metro to construct
this 1.9-mile completely underground
transit way through downtown Los
Angeles, the second most highly
populated metropolitan area in the U.S.
The new line will increase downtown
transit options with three new stops at
state-of-the-art underground stations -
the existing, but reconstructed, Little
20 AUGUST 2021 | UCONonline.com
Tokyo/Arts District Station; the completely
new Grand Av Arts/Bunker Hill Station;
and the Historic Broadway Station
located at Broadway and 2nd Street.
While the tunnels for the twin rail
lines were excavated with a 400-foot
tunnel boring machine, the stations were
excavated by open cut. In order to open
cut to the needed depths in a high-density
metropolitan area, the contractors first
had to safely get past numerous older
utilities, many of which needed repair
or replacement. The Historic Broadway
Station was the most challenging to
construct, due to having the most
congested existing underground utilities
in the area, including a 10-foot-diameter,
reinforced concrete (RCP) storm drain
that had been constructed around 1960.
Unique concept
A creative construction sequencing
plan devised by RCC would expose the
existing utilities along the 400-foot
station zone to make any repairs or
replacements. These exposed utility
lines would then be suspended for
perhaps as long as four years over what
would soon be 50 to 60 feet of air.
The electrical, telephone, fiber optic
and natural gas lines were easily enclosed
in a suspended casing, but the 10-foot
diameter RCP storm drain belonging
to the LA Flood Control Department
was a larger and heavier challenge. The
contractors immediately realized that
due to its weight and uncertain structural
integrity, the existing concrete storm
drain would have to be either re-routed
or replaced with something lighter.
Hobas centrifugally cast, fiberglass
reinforced, polymer mortar (CCFRPM) pipe
was chosen as the lighter, stronger, less
expensive, and more efficient option for
the project. Hobas pipe is six times lighter
than RCP, and its ease of installation is
due partly to its push-on joints that allow
fast assembly. Skanska crews had recently
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Underground Construction - August 2021

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