Osterberg Memorial Lecture: Rock-Socketed Drilled Shafts - The State of Practice-PPT Presentation

PPT Presentation

Pdf Summary

The presentation reviews 30 years of progress in the design, construction, and structural analysis of rock-socketed drilled shafts, highlighting Jorj Osterberg’s contributions and the bi-directional static load test, now standardized as ASTM D8169.<br /><br />For axial design, side and base resistance can be combined. Design methods supported by load-test evidence estimate these resistances using rock strength and rock-mass conditions. Conventional, stable sockets excavated without support are considered “normal” sockets; recommendations for weaker rock apply when support is needed. The Hoek–Brown criterion helps characterize bearing resistance in fractured rock. Load-test results indicate that, in properly designed, constructed, and inspected shafts, side and base resistance are generally mobilized at displacements compatible with typical structural settlement tolerances.<br /><br />The presentation cautions against relying on Rock Quality Designation (RQD) alone: it is useful for flagging zones requiring further investigation, but may misrepresent rock-mass conditions. Acoustic and optical televiewer surveys can provide better information about socket stability and likely resistance.<br /><br />Construction and quality assurance have also improved. Reliable base cleanout is essential for using base-resistance design values confidently. Inspection tools—including weighted soundings and devices that measure sediment thickness or penetration resistance—help verify base conditions. Better understanding of tremie-concrete workability and stability supports concrete placement quality.<br /><br />Finally, rock sockets are treated as disturbed regions in structural design and analyzed using strut-and-tie models. These models help assess concrete compression and reinforcing-steel tension, enabling practical, less congested reinforcement designs, including for sockets in strong rock.

Keywords

rock-socketed drilled shafts

axial design

bi-directional static load test

ASTM D8169

side resistance

base resistance

Hoek-Brown criterion

RQD

televiewer surveys

strut-and-tie models