Drilled Shaft Gravelly Sand and Gravel QZ

No load tests are available to characterize the end bearing of drilled shafts in gravelly sand and gravel. The tip resistance of shafts whose side resistance uses the Rollins gravelly sand or gravel curves is taken from the Drilled Shaft Sand q-z model of Reese and O'Neill (1988), with the ultimate end bearing from the uncorrected SPT blow count ($q_u$ = 0.6 $N_{SPT}$ tsf, 30 tsf for $N_{SPT}$ above 50, reduced for base diameters over 50 in) and the same normalized load-transfer curve.

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[O'Neil et al., 1999] O'Neil, M. W., Reese, L. C., et al. (1999). Drilled shafts: Construction procedures and design methods. Publication FHWA-IF-99-025, Federal Highway Administration.