After snaking through a subterranean obstacle course of utilities, foundations, methane gases and various urban structures, the 22-ft-diameter tunnel-boring machine (TBM) dubbed "Angeli" broke through to its termination point at Fourth and Flower streets in downtown Los Angeles on July 19. It marked a key milestone in the $1.7-billion, 1.9-mile Regional Connector project—the "missing link" that will connect existing rail lines for seamless rides throughout Los Angeles County.
Having completed the first of twin tunnels between Little Tokyo west to downtown in five months, Angeli will now be disassembled over the course of five weekends and brought back to the original launch site to begin the second tunnel this fall, says Gary Baker, project director with the Los Angeles County Metropolitan Transportation Authority (Metro). BIM-assisted design and Shape Accel Arrays—a system of wireless sensors—helped Angeli navigate through extremely tight tolerances and situations of very shallow cover.