CPT based direct design of bridge foundations-PPT Presentation

PPT Presentation

Pdf Summary

The presentation describes a direct cone penetration test (CPT)-based approach to designing driven pile foundations for highway bridges in California. CPT measurements—including cone tip resistance, sleeve friction, friction ratio, and pore pressure—are used to characterize subsurface conditions and estimate soil properties such as friction angle, undrained shear strength, residual shear strength, and soil behavior type.<br /><br />Pile capacity is estimated using the LCPC method of Bustamante and Gianeselli. The method uses CPT resistance and soil classification to calculate unit shaft friction and end bearing, applying factors and maximum resistance limits based on soil type and pile category. For open-ended steel pipe piles, the analysis considers both plugged and unplugged behavior, which affects the effective tip area and calculated end resistance. The presentation outlines the steps for determining equivalent average cone resistance around the pile tip and combining shaft and end resistance to estimate nominal pile capacity.<br /><br />The approach is illustrated with resistance profiles for a pipe pile and compared with dynamic pile testing. For a 24-inch-diameter, approximately 70-foot-long pile, CAPWAP analysis of the initial drive estimated 214 kips of toe resistance and 275 kips of shaft resistance, for 489 kips total. A restrike after 21 days showed substantial soil setup: driving resistance increased from 422 to 1,021 kips, corresponding to a setup factor of 2.4.<br /><br />Overall, the presentation demonstrates how CPT data can support pile design and how PDA/CAPWAP results and restrike testing can help evaluate predicted resistance and time-dependent gains in capacity.

Keywords

cone penetration test

CPT

driven pile foundations

highway bridges

LCPC method

pile capacity

shaft resistance

end bearing

CAPWAP

soil setup