Historic Storm Drain Tunneling Revealed by Los Angeles Metro Subway Construction - NAT2024

This case history provides a physical benchmark of tunneling technology progress comparing an old hand-mined tunnel to a modern 20-ft-diameter EPB TBM that mined in the same ground. This rare opportunity to see how tunnels were constructed many years ago occurred when an old 10-ft-diameter storm drain tunnel in the way of 􀀯os Angeles subway construction was demolished and replaced with 􀀫obas 􀀋􀂿berglass􀀌 pipe. Steel rib and lagging initial support was exposed showing solid-sawn 2" × 12" × 48" redwood lagging. This paper documents the as-built old tunnel, how it was successfully replaced, and some lessons learned.