NEAR FAILURE OF THE ALL AMERICAN CANAL IN SOUTHERN CALIFORNIA DUE TO A 7.2 MAGNITUDE EARTHQUAKE IN APRIL, 2010

摘要

On Easter Sunday, 2010, a 7.2 magnitude earthquake struck northern Mexico near Mexicali. The All-American Canal, which diverts Colorado River water from the Imperial Reservoir and delivers irrigation water throughout the Imperial Valley, was heavily damaged. The canal parallels the California/Mexico border and the siphon carries water across the New River in southern California only 22 miles from the earthquake epicenter. The earthquake damaged the concrete canal lining, separated vertical and horizontal joints at the inlet of the siphon and wasteway, liquefied materials in the New River channel, and opened up wide cracks and fissures in the 40-foot-high embankment fill and riverbank supporting the canal, gate structure, siphon and wasteway. Concentrated seepage was observed exiting near the toe of the embankment fill between the siphon and the wasteway. Many aftershocks occurred, but the seepage remained steady for another week after the April 4~(th) main shock. Eight days after the initial earthquake, the quantity of seepage suddenly increased approximately ten fold. That evening a significant aftershock of 4.8 magnitude occurred, and the seepage increased even more causing internal erosion of embankment materials to begin in earnest. This paper discusses the incident, what mitigation actions were taken that night to save the siphon structure, follow-up investigations and continuing engineering studies.