The National Academies

NCHRP 24-30 [Final]

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

  Project Data
Funds: $499,758
Research Agency: Brigham Young University
Principal Investigator: Kyle Robins
Effective Date: 6/2/2006
Completion Date: 1/30/2011

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.   However, verified design guidelines for determining the increase in pile lateral resistance resulting from soil improvement were not available. The objective of this project was to develop such design guidelines.

The research entailed review of relevant practice, test data, existing specifications, and research findings to develop a comprehensive list of soil improvement techniques for increasing the lateral resistance of piles in specific weak soil types (e.g., soft cohesive, organic, loose granular, or sensitive soils).  Full-scale field tests were conducted to measure the effect of soil improvement techniques for single piles and pile groups.  Test results were evaluated using finite-element analysis and parametric studies were conducted. Based on the parametric studies, design guidelines were developed to estimate site improvement.

The guidelines and research report were published as NCHRP Report 697.  

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