Industry NewsTransportationTunnel Boring

First of two tunnels for the Regional Connector Transit Corridor completed

The area below ground in Los Angeles, CA is the scene of state-of-the-art engineering achievements. German high-tech tunnel-boring machines (TBM) from Herrenknecht are creating underground arteries for the city. One TBM, named Harriet, successfully completed her drive for the Crenshaw/LAX Transit Project in April 2017. A second TBM, named Angeli, finished digging the first of two tunnels for the Regional Connector Transit Corridor on July 18. From spring 2018 onward, the tunnel boring stars will have additional company: for each of the Purple Line Extension Sections 1 + 2, two more Herrenknecht TBMs will be working their way through the difficult ground. All three projects are part of the strategic subway extension in L.A. to relieve the traffic above ground.

Los Angeles suffocates in traffic during rush hour. For this reason the Los Angeles Metropolitan Transportation Authority (Metro) is pushing ahead at full speed with the expansion of local transport links. In the coming years, the existing metro rail network will be expanded in a number of different places. The latest example is the Crenshaw/LAX Transit Corridor. The nearly 14 km (8.7 mile) long new light rail route will improve the connection between the urban centers of Crenshaw and Inglewood as well as the region around Los Angeles International Airport (LAX). LAX passenger numbers alone show the high demand for public transport capacity: in 2016, more than 80 million passengers were processed — and the trend is rising.

Between May 2016 and April 2017, Harriet worked its way forward underground for a section of the Crenshaw/LAX Transit Corridor. The TBM (6.51 m or 21 ft) first excavated a 1.6 km (1 mile) long tunnel between the future stations of Expo/Crenshaw and Leimert Park. It was then disassembled and transported back to the launch shaft for the second, parallel section. In April 2017, Harriet, completed her mission below Los Angeles with the second breakthrough in the target shaft at the Leimert Park station. With a 24-hour best performance of 43 m (141 ft) a new record in mechanized tunneling with a subway sized EPB Shield was set for the city of Los Angeles — four more times, 40 or more meters were created within one day. Thanks to weekly best performances of 170 m (557 ft), the Crenshaw/LAX Transit Corridor is expected to go on line on schedule in 2019.

In February 2017, the EPB named Angeli got under way. The TBM is boring a section of the Regional Connector Transit Corridor. It will link the existing Gold, Blue and Expo Metro Lines to new and faster direct connections. From 2020, this will allow locals and visitors to travel north-south from Azusa to Long Beach and east-west from East Los Angeles to Santa Monica without having to change. Angeli has just finished the first of two 1.7 km (1.1 mile) long tunneling routes. On July 18, she reappeared in the target shaft at 4th Street. Next she will dig a parallel tunnel with the final breakthrough scheduled for the end of the year.

One of the greatest challenges in mechanized tunneling under Los Angeles are the possible gas deposits. In order to master these safely, the contracting joint ventures have opted for special technology from Herrenknecht. The electrical components in Harriet and Angeli are explosion-protected so that safe tunneling can be realized at all times. This measure has previously proved its worth worldwide in various reference projects.

In the meantime, designers and engineers at the Herrenknecht headquarters in Schwanau are already working on the next order for Los Angeles. The existing Purple Line is also planned to grow by 14.5 km (9 miles) and seven stations. To this end, in both the spring of 2018 and the spring of 2019, two additional Herrenknecht EPB shields each are to be launched. In just a few years the four machines will produce more than 11 km (6.8 miles) of high-quality tunnel tubes. A decade ago, under similar conditions, two EPB Shields from Herrenknecht had already built a total of 4 km (2.5 miles) of tunnel for the expansion of the Gold Line. Herrenknecht technology in Los Angeles is thus already a real success story. To be continued.


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