A Race Against Time

by Julie Mark Cohen, P.E., Principal; JMC Engrs., Troy, NY,


Serial Information: Civil Engineering—ASCE, 1999, Vol. 69, Issue 11, Pg. 52-55


Document Type: Feature article

Abstract:

The coastal hillsides of San Mateo County, California, were quickly developed during the post WWII construction boom. Although the land is prized for its scenic beauty, the underlying bedrock�described by geologists as Franciscan assemblage�is prone to landslides. In January 1997, a landslide caused the closing of Polhemus Road, an important 2 mi (3.2 km) long, 2-lane thoroughfare. Because the soil on the road threatened power poles, an essential water pipe buried below, and a creek, engineers designed a soldier beam retaining wall with tie-backs at the base of the hill. However, in January 1998, heavy rains accelerated the slide movement. The backyards of the houses on top of a hill by the roadside had lost 20 ft (6 m) of their backyards, and the soil surcharge on the road had grown from 10 ft (3 m) to 24 ft (7 m). The creek slope also needed to be stabilized, so HDP pipe covered with rock was placed along part of the creek bottom. By June 1999, construction of the bottom retaining wall was complete.

Subject Headings: Rivers and streams | Highways and roads | Retaining structures | Landslides | Hydro power | Highway and road design | Construction management

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