Design Guidelines for Increasing the Lateral Resistance of Highway-Bridge Pile Foundations by Improving Weak Soils

Lateral resistance of pile foundations typically is controlled by the stiffness and strength of the soil in the vicinity of the pile cap and the soil surrounding the upper portion of the piles. When the surrounding soil is weak, the design of the foundations may be controlled by lateral loads requiring additional or larger piles. Geotechnical design studies indicate that a significant increase in pile lateral resistance may be achieved with soil improvement. Soil improvement extending a nominal distance around and below the pile cap may produce a soil system with increased capabilities to resist lateral loads. Soil improvement techniques such as removal and replacement, dynamic compaction, grouting, and soil mixing may be more cost-effective for increasing lateral resistance than installing additional piles or increasing pile diameters. At present, there are no verified design guidelines for determining the increase in pile lateral resistance resulting from soil improvement. Practical design guidelines to determine the magnitude of increase in lateral resistance as a function of the magnitude and extent of the soil improvement need to be developed and verified with documented sophisticated analysis and full-scale field tests. The objective of this project is to develop design guidelines for determining the effect of soil improvement on the lateral resistance of piles in bridge foundations.