SMALL CITIES/RURAL COMMUNITIES PROJECT OF THE YEAR: DISASTER OR EMERGENCY CONSTRUCTION REPAIR
San Ramon Canyon Storm Drain Project Managing Agency: City of Rancho Palos Verdes, California Primary Contractor: L.H. Woods & Sons, Inc. Primary Consultant: Harris & Associates Nominated By: City of Rancho Palos Verdes, California
onstruction of the San Ramon Canyon Storm Drain Project was urgently needed to manage stormwater runoff and debris that repeatedly closed a major thoroughfare into and out of the City of Rancho Palos Verdes. The stormwater events also threatened the property and lives within a mobile home community located directly below the street. Another factor the City considered was the significant erosive impact the stormwater was having on the landslide-prone canyon walls in the upper section of the Canyon. The project includes installation of a 4,000-foot-long, 54-inch diameter, thick-walled steel drainage pipe, running from the middle of San Ramon Canyon just east of the PVDE switchbacks to the ocean. The inlet structure located in the upper canyon, which functions to direct storm flows from the streambed into the pipe, is founded on 60-foot concrete piles capped with cast-inplace grade beams that were installed in 2013. The above-ground structure is built from “shotcrete,” which is applied to a built-inplace reinforcing steel cage using a highpressure hose. The exposed surface was
finished using hand tools by skilled craftsman to create a smooth surface in order to improve hydraulic efficiency. The inlet structure is built around the upper end of the 54-inch pipe that was installed after the tunnel was built. Inside the tunnel, the pipe was surrounded by an expanding grout to lock it in place and fill the annular space between the outside of the pipe and the inside of the tunnel. The pipe was installed using several methods including two types of tunneling, and a more traditional “cut and cover” section. The longest section of tunnel runs from just south of Palos Verdes Drive South up to the inlet structure in the canyon. Tunneling was the primary construction practice used on over half
of the pipe’s alignment to minimize the impact of sound, vibration and dust that might otherwise have affected the community adjacent to the construction, as well the natural preserve areas that surrounded the work. The tunneling work was accomplished with two 37-foot-long tunneling machines built especially for the project and a collection of experienced and dedicated miners. As the upper tunneling machine chewed its way through the earth, the miners constructed a “barrel” right behind it using curved steel beams and wood lagging to keep the excavated space open and intact. The lower tunneling machine and steel sleeve were advanced using a hydraulic ram from the bluff-top, with excavated materials backed out on a conveyor system. Ventilation, water, power, rail, and rib and lag materials had to be advanced behind the machines in a complex process. The Storm Drain was successfully completed and now provides a significant benefit to the local community through improved flood protection and safer, more dependable traffic access to the entire Palos Verdes Peninsula.
July 2015 issue of the APWA Reporter, the official magazine of the American Public Works Association