The underworld of Los Angeles holds surprises in store. If you bore tunnels here, you primarily cut through well-known clay and siltstone. But repeatedly, football-sized boulders get in the way: hard work for the cutter of a cutting wheel. “You have to be careful when you encounter explosive gases – or oil- and tar-bearing sand,” says Chris Hebert, who heads the tunneling division of US contractor Traylor Bros. Inc. His currently most important projects contribute to the expansion of the Los Angeles Metro Rail.

Until the new metro lines go into operation, there is plenty for him and his people to do – and for the three Herrenknecht TBMs Traylor Bros. is using. “The machines are tailored exactly to our requirements,” says Chris Hebert. “They are explosion-proof in case we encounter gas. Moreover, they are equipped with tools and systems to assist us in handling all the types of ground we will encounter, including the sticky tar sands “says Hebert. “Our partners at Herrenknecht don‘t just deliver a machine. Together with the customer, they find a solution to every challenge.”