Capacity of Hydraulically Jacked Piles-Paper

Paper

Pdf Summary

The paper examines the capacity and installation of hydraulically jacked steel piles, commonly used to underpin, stabilize, or strengthen existing foundations. These piles are pushed into the ground in connected segments using a hydraulic ram, with the structure’s weight typically providing the reaction force. Each pile can be proof-tested during installation.<br /><br />Analysis of more than 1,500 installation tests shows that pile capacity generally increases with penetration length and soil resistance measured by Standard Penetration Test (SPT) blow counts. However, the data exhibit substantial scatter. Existing empirical methods, including a modified Meyerhof-based approach, predict capacity and required depth poorly. Soil type also appears to affect the relationship, while installation procedures, crews, and testing practices may contribute to variability. The authors caution that their proposed equations and charts are crude estimates and should not be used as reliable design tools.<br /><br />The paper outlines recommended installation and proof-testing procedures. It advises considering both dead and future live loads when determining pile spacing and capacity, applying an appropriate safety factor, minimizing load eccentricity, and evaluating closely spaced piles for group effects. For proof testing, the authors recommend loading each pile to at least 150% of its design allowable capacity, measuring movement, and holding the load until settlement stabilizes.<br /><br />The authors conclude that capacity should be verified by proof-testing every pile. Test installations can help estimate required pile lengths, but standardized installation and testing procedures, along with further research, are needed to improve prediction methods and reduce data variability.

Keywords

hydraulically jacked steel piles

underpinning foundations

pile capacity

installation tests

soil resistance

Standard Penetration Test

proof testing

pile settlement

Meyerhof method

foundation stabilization