By Lynda Myer
The tunneling process of Los Angeles for the D Line Subway Extension has been completed.
Linking downtown LA with West LA, this project required tunneling through one of the most densely populated urban corridors and challenging geology in the region.
With an average advance of 12-18m per day, a 6.4m-diameter closed face TBM was benefited to build this 14.5km tunnel.
As Lindsey Horvath, chair of the LA County Board of supervisors and Los Angeles County Metropolitan Transportation Authority (Metro) board member, stated; the D Line Subway Extension was one of the most complex engineering feats Metro had undertaken.
Considering that this project is advancing through tar sands in southern California, during the five years of excavation it encountered many technical challenges, including gassy ground and abandoned oil wells, while it is the longest tunneling project. In order to probe the earth and identifying and removing potential objects before any TBM damage, near the La Brea Tarpits, where the TBMs encountered tar sand, horizontal directional drilling was used. The same method was used to identify and avoid unmapped and abandoned oil wells underneath Beverly Hills High School.
Following that the tunneling was completed, Metro is going to continue to work with its two contractors as a part of a joint venture with Skanska-Traylor-Shea and Tutor-Perini/O&G to complete seven new underground stations in Section 1 between Wilshire/Western and Wilshire/La Cienega, Section 2 between Wilshire/La Cienega and Century City, and Section 3 between Century City and Westwood.
While the scheduled date for inauguration of Section 1 is next year, Section 2 will be opened in 2026 and Section 3 in 2027.
