Liquefaction at the Meloland Overcrossing During the Imperial Valley Earthquake of 1979

Abstract

The Meloland Overcrossing is located 0.3 mi from the Imperial fault and was shaken by ground surface motions of up to 0.3 g during the Imperial Valley earthquake of 1979 (magnitude M = 6.4). While there was no significant damage to this instrumented highway bridge or any reported surface evidence of subsurface liquefaction, it is assessed that liquefaction occurred in up to three layers at the site at various times during the first eight seconds of shaking. A modified level ground liquefaction analysis after Seed and others (1983) was used to assess such time dependent development of liquefaction. Results from such evaluations were used to assess and explain anomalies in the lateral and rotational responses of the central pier pile foundation demonstrating that the central pier of the Meloland Overcrossing came periously close to complete collapse during this event. This is contrary to the bridge designer9s belief that this highway bridge performed quite well during the earthquake as characterized solely by the lack of observable damage to the bridge. It is further suggested that the time dependent evaluation of liquefaction demonstrated herein can be used on other projects where one likewise wishes to assess the amount of deformation (e.g., the rotationally induced settlement in the case of Meloland) that is likely to ensue.