ABSTRACT:

Geotechnical studies were conducted for the Vincent Thomas Bridge as a part of the seismic retrofit design program. The foundation of the bridge tower is located immediately next to a channel edge and is supported on a group of 167 piles. Site stability of the channel edge would have significant impacts on seismic performance of the bridge. Using design ground motions adopted for the bridge retrofit program, deformation analyses have been conducted to estimate permanent displacements of the slope. Newmark's sliding block analysis was used along with seismic coefficient time histories computed from two dimensional site response studies which account for compliance of the slope and spatial variation of motions within the soil block. With the estimated free-field ground displacements, pile stresses were examined to assess pile survivability due to kinematic loading from the deep-seated ground failure.

INTRODUCTION

The Vincent Thomas Bridge, constructed in the early 1960's, is one of the seven major toll bridges in the State of California to undergo seismic retrofit by the California Department of Transportation (CALTRANS). The bridge is located at the entrance to the Port of Los Angeles and is a cable-suspension structure, approximately 1848 meters long. The main suspended span is 457 meters and crosses over a major shipping channel for the Port. The main cables of the bridge rest in saddles at the towers and at the cable bents. The cables are then connected to massive anchorage blocks that are supported on battered pile foundations. The towers are tapering cellular shafts of 102 meters in height supported also on pile foundation at the edge of the channel. As a part of port improvement by the Port of Los Angeles, the channel would be deepened from the existing 10 meters water depth to 15 meters to allow passage of larger container vessels.

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