Geotechnical Design of a Bridge Widening Project in a Highly Active Seismic Region of Southern California

This paper presents geotechnical issues and our design approaches for the Upper Oso Reservoir Bridge Widening located along State Route 241 in Mission Viejo, California. The total bridge length is approximately 1540 feet (470 m). The foundations of the existing bridge structures consist of 36-inch (0.91 m) diameter cast-in-drilled-hole (CIDH) piles and driven steel H-piles. The subsurface materials at the bridge site were investigated by a field exploration program. Key geotechnical design involved development of new seismic design parameters and acceleration response spectra for an Upper Level Earthquake (ULE) and a Lower Level Earthquake (LLE); evaluation of new fill and liquefaction-induced settlements on the existing and new foundations; pile foundation modeling and capacity assessment; abutment slope seismic stability and deformation.