â€œPrediction of Side Friction of Drilled Shafts in Very Dense Fine SANDâ€ UAE

Video Transcription

Video Summary

The presentation examines the design of drilled-shaft foundations for nine large, prestressed concrete water-storage tanks in Ras Al Khaimah, UAE. The site is underlain mainly by very dense, fine, uncemented sands, with SPT values generally above 50 and high shear-wave velocities. Groundwater is very deep. Some tank areas contain fill, requiring ground improvement.<br /><br />The tender design specified numerous 30 m piles. Conventional design methods for piles in sand predicted low shaft friction and therefore long piles. Because the sands were highly overconsolidated and exceptionally stiff, the project team assessed them using the Category 3 intermediate geomaterial (IGM) model. This approach predicted substantially greater shaft resistance than the conventional beta method and supported reducing pile lengths to about 25 m.<br /><br />Static and dynamic load tests during construction confirmed satisfactory performance. Static-test interpretations generally indicated overall safety factors of 3–4, while measured displacements were small. The revised design reduced nominal pile lengths by roughly 25%, producing significant cost savings.<br /><br />The presentation concludes that very dense regional sands should not automatically be treated as ordinary sands. Geophysical investigations can improve understanding of their stiffness and continuity, and instrumented pile tests are valuable for calibrating design assumptions.

Keywords

drilled-shaft foundations

prestressed concrete tanks

very dense sands

intermediate geomaterial

pile load testing

shaft resistance

ground improvement