An Evaluation of Increased Lateral Loads on Bridge Foundations Due to Liquefaction

The results of a lateral spread study are presented in this paper for a bridge-widening project in Southern California. The existing bridge spans a creek underlain by loose to medium dense, saturated sands. The site is highly susceptible to liquefaction in the event of the design earthquake. Our primary geotechnical design concern was the possibility of bridge collapse resulting from a liquefaction induced slope failure against the deep foundation at the abutment. A combination of limit equilibrium and displacement based analysis techniques were used to assess the problem, and to estimate the shear and moment demands on the new large diameter CIDH pile foundation. By installing a single row of stone columns at the mid-height of the abutment slope, we were able to demonstrate that the estimated lateral load resulting from liquefaction would not exceed the plastic capacity of the proposed deep foundation. Our approach was generally consistent with the recently published, and AASHTO sponsored, NCHRP 12-49 project regarding seismic design guidelines for new bridges and the effects of seismic displacements against bridge foundations.