LA METRO | BTS
Left and far left:
Gold Line EPBs selected by contractor, and including long screw conveyors.
Below left and below: TBM hole through and finished tunnel images from Gold Line.
greatly helped with soldier piles and lagging/dewatering, installing decking and hanging utilities. At the Veterans Affairs Hospital, the station is in the
parking lot, enabling activities usually done in the street to be performed more efficiently. However, the site also had all the mission-critical utilities for the hospital, including a steam tunnel. For the arched roof there had to be excavation through the black, tar-impacted or asphalt-impacted soil. Tar also came in on the water. The contractors dealt with it very well. Methane and hydrogen sulphide are dissolved in the
water. Drainage layers are behind station concrete and the gases come out of solution after which a system, like inverted roof-drainage, was employed to ventilate safely to the surface. LA was essentially built on oil fields. We know roughly where many wells are, but only approximately, and any wells to be abandoned, if in the way, must be done so to the latest standards. For example, near Beverly Hills High School some wells were being abandoned as the project was underway. Horizontal directional drilling (HDD) and magnetometer
surveys help to locate wells in the tunnel envelope. With three holes and triangulation, the locations are worked out. Again, due to Covid, the school was not operating, and this helped with two wells that were found. HDD also helped to locate other metallic obstructions, such as old soldier piles, to cut them off ahead of tunnel excavation. Another interface involved tunnelling beneath a
large diameter high-pressure water transmission line. Permeation grouting provided increased assurance. On Section 3, we encountered soldier piles beneath
a building, that were from temporary support of excavations in the past, as shown in old as-built drawings. Boreholes and a magnetometer found the depth of the piles, which then allowed the tunnel vertical alignment to be kept within a couple of feet of the bottom of the piles, i.e., as high as reasonably possible, for the pressure to remain below 4 bar and permit successful interventions. An old bank vault was found at the entrance to a station, and an
old adit that had been backfilled. That turned out to be a robbers’ tunnel, built in 1987. They robbed two vaults and apparently planned to come back for the third.
FUTURE PROJECTS LA Metro has many future projects, three with tunnels: the Sepulveda Transit Corridor; the K Line Northern Extension; and, the E Line Extension to East LA, which extends the Gold Line. The Westside and the Los Angeles Basin are separated from the San Fernando Valley by the mountains. Traffic through Sepulveda Pass is stationary for much of the day. There are tunnel options for several alignments. Preliminary engineering and site investigation are underway. The K Line Northern Extension would go through an urban area to connect the line to Santa Monica with the Purple Line, the Red Line and Hollywood. The E Line Extension includes about twin-bore tunnels and three underground stations.
Below: Layout of Purple Line Extension project
WPLE MAJOR FEATURES
● Constructed in 3 sections ● 14.5 km, all underground ● Twin bore tunnels ● 7 underground stations ● Maintenance facility for non-revenue vehicles ● 70 New rail vehicles ● Planning began 2007 ● Construction all segments projected 2027
June 2026 | 17
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