Combined Side and Base Resistance in Rock-Socketed Drilled Shafts-Video

Video Transcription

Video Summary

The presentation argues that designers should routinely combine side and base resistance when designing drilled shafts socketed in rock. A common concern—that the two resistances mobilize at incompatible displacements—is not supported by bidirectional load-test evidence: both can develop substantial resistance at small, compatible movements in properly designed, constructed, and inspected sockets.<br /><br />The speaker highlights advances in subsurface investigation, construction, and inspection that make this approach more reliable, including improved rock coring, geophysical tools, shaft-cleaning methods, and underwater inspection devices. A St. Louis bridge project illustrates the potential savings: using both resistances and a full-scale load test reduced the number and length of shafts, saving about $10 million.<br /><br />Caution remains appropriate in highly variable or soluble rock, such as karst, but these conditions call for better investigation rather than automatically ignoring base resistance. The speaker’s key recommendation is to use adequate site characterization, sound geotechnical and structural design, careful construction, and verification to optimize foundations and reduce cost and waste.

Keywords

drilled shafts

rock sockets

side resistance

base resistance

bidirectional load test

bridge foundation savings