Orange County Branch Newsletter

July 2015


A Storm Drain Success Story: Two Tunnels & a Landslide

By Bita Sadri, P.E.

At the Orange County Branch Environmental and Water Resources Institute (OC EWRI) June Luncheon, Mr. Randal Berry, P.E., Design Manager of Harris & Associates in Irvine, presented on the 2014 American Public Works Association award winning Project, San Ramon Canyon Storm Drain in Rancho Palos Verdes.

Mr. Barry discussed the challenges and innovations associated with a $17.7 million storm drain project along San Ramon Canyon in the affluent coastal city of Rancho Palos Verdes in Los Angeles County. The adjacent active Tarapaca Landslide was feeding debris into the canyon which large rain events transported to 25th Street below.  More than 250 homes were in harm’s way and access was threatened to both 25th Street and Palos Verdes Drive East (PVDE) Switchbacks.

The Harris Team developed a well-designed solution using trenchless technology, which required two tunnels and a gravity buttress fill design to divert the collected stormwater to the ocean at the bottom of the coastal bluffs, shore up a deficient drainage system downstream, and stabilize an active landslide

The focus of the presentation was on the design and construction of the following critical project elements:

  • Lower Tunnel (300’ long, 80” hand-mined tunnel in solid bedrock at 38% grade atop a 150’ high Pacific Ocean coastal bluff)
  • Upper Tunnel (2,000-foot long 80-inch rib & lagging tunnel though a dormant landslide at 13% grade that was as much as 90-feet deep below PVDE)
  • Inlet & Outlet Structures (requiring CIDH piles with grade beams and tieback anchors)
  • Access Road & Gravity Buttress Fill (restoring the natural canyon while maintaining access)

Mr. Berry delivered a wonderful presentation of the trenchless technology. The San Ramon Canyon Storm Drain in Rancho Palos Verdes project was unique and highlighted unique engineering challenges and provides safer access to the entire Palos Verdes Peninsula. The presentation and lessons learned from the project was very inspiring and unique for me as a young engineer. I hope one day I get to work on an exciting and unique project like this.