Abstract

The Interstate I-5 / Interstate I-805 Improvement Project is designed to relieve a major traffic congestion in the northern part of the city of San Diego in California. This whole area is considered to be in seismic zone 4 and the seismic design loading was based on a site specific Acceleration Response Spectra curve developed for each bridge structure.

The project is being built by E. L. Yeager Construction Co. at a total project cost of about $125 Million. The portion of the cost to do the various bridges and structures is about $65 Million with the balance of the project cost devoted to do the roadway section of the project.

There are 4 major interstate freeway bridge widenings on both sides of the existing bridges, 4 new truck connector bridges, a plantable geosynthetic reinforced retaining wall and other 17 earth retaining walls on this project.

The bridge design has been a challenge since the new widening is not structurally similar to the existing one thus resulting in incompatible design criteria. The deep foundation design for all structures paused a considerable challenge, as the liquefaction potential is considered moderate to high. The high water table coupled with the fact that the whole construction area is less than a mile from the Pacific Ocean has lent itself to liquefaction potential in case of a high magnitude earthquake. The deep foundation design typically has single shafts/caissons with the top portion of the piles encased with a cylindrical permanent steel casing and the bottom portion of the pile is a rock-socket Cast In Drilled Hole (CIDH) pile.

This project has all the conceivable constraints on a construction project, viz. railroads, existing interstate highways, city streets, environmentally sensitive areas (ESA), creeks and a lagoon. All these constraints have paused a considerable challenge on the design and construction of the various structures.