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Purple Line Extension Tunnel Boring Machines (TBM)

The two Tunnel Boring Machines (TBMs) for the Purple Line Extension Transit Project Section 1 will be used to dig two parallel tunnels that will connect three new stations between Koreatown and Beverly Hills.

The TBMs will dig side by side starting at Wilshire/La Brea in the Miracle Mile section of Los Angeles and continue towards Wilshire/Western in Koreatown. Then they will be disassembled for transporting back to Wilshire/La Brea and then reassembled for the last leg of their journey through Wilshire/Fairfax and finishing at Wilshire/La Cienega in Beverly Hills.

When will they start work?

The TBMs will start work in Fall 2018 after they have been assembled and tested.

For more information about the TBMs check out this factsheet .

Follow ElsieSoyeonTBMs on Twitter for weekly updates on their progress and more.

Tunnel mining on Wilshire Bl

The Purple Line Extension Transit Project will construct two parallel tunnels to create a seamless connection from the current Purple Line Wilshire/Western Station in Koreatown to three new stations located at Wilshire/La Brea, Wilshire/Fairfax, and Wilshire/La Cienega.

The new 3.4 mile railway will be constructed using a combination of tunnel boring machine and an “open-cut” methods. The Twins will be responsible for approximately 17,845 linear feet of tunneling, as they travel under Wilshire Bl. Each tunnel will take approximately 24 months to complete.

Along the way, The Twins will encounter different soil conditions. The tunnel crown will always be at least 20 feet or more under the subsurface water table.

In terms of geology, tunnels will be bored through two types of geological formations: San Pedro and Fernando.

The following ground conditions may be encountered during tunneling:

  • Full face San Pedro
  • Mixed face ~ Top San Pedro and bottom Fernando
  • Full face Fernando
  • Between STA~490+00 (Dunsmuir Av) and 540+00 (Crescent Heights Bl) equals~ 5,000 linear feet. These three ground types will also be saturated with tar (with various percentages of saturation/presence).

Tunneling Statistics

Progress is measured in total linear feet traveled and the number of rings they build.


Linear Feet




La Brea Bl to Western Av



La Brea Bl to Fairfax Av



Fairfax Av to La Cienega Bl



La Cienega Bl to tail track west of La Cienega Bl

Totals: approximately 17,845 linear feet or 3.4 miles; two tunnels equal approximately 35,690 linear feet or approximately 6.8 miles.

Follow ElsieSoyeonTBMs on Twitter for weekly updates on their progress and more.

Meet the Winners

The Purple Line Extension, Section 1 Tunnel Boring Machine Art and Naming contest was a historical event.  A panel of judges made up of community leaders helped select the finalists from over 60 entries across Los Angeles County, while over 3,500 votes were casted for the prize-winning art and names.

The names “Elsie” and “Soyeon” (pronounced “So-Yun”) were selected from a winning entry submitted by 9 th grade, Fairfax High School student, Marianne Gutierrez. Soyeon is Korean for “bright” and “beautiful” and was named after female astronaut and mechanical engineer Yi Soyeon. Elsie was named after Elsie Eaves, the first female to be elected as a member of the American Society of Civil Engineers.

Lauren Park, a third-grade student from Palm Crest Elementary in La Canada who also goes to Prism Art School in Koreatown after school, won the art contest. Her winning illustration showed her ideal community, which included Purple Line Extension service.

The new artwork for the Purple Line Extension’s tunnel boring machines. From left, Metro Deputy CEO Stephanie Wiggins, L.A. Council Member David Ryu, naming contest winner Marianne Gutierrez, artwork contest winner Lauren Park, L.A. Mayor Eric Garcetti and former Supervisor Zev Yaroslavsky.

Follow ElsieSoyeonTBMs on Twitter for weekly updates on their progress and more.

Please use the materials below to learn more about the Regional Connector Tunnel Boring Machine (TBM).

Follow ElsieSoyeonTBMs on Twitter for weekly updates on their progress and more.

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