Drilled Shaft Limestone TZ (McVay) [McVay and Niraula, 2004]

[McVay and Niraula, 2004] measured the side resistance of 6 ft diameter drilled shafts in synthetic limestone with unconfined compressive strengths of 10, 20 and 40 tsf in the centrifuge. The unit skin friction curves, normalized by the ultimate unit skin friction and by the shaft diameter, collapse onto a single curve that also agrees with the normalized curve of Kim (2001) from 33 Osterberg tests in natural Florida limestone (Figures 5.5 and 5.6, Eqs. 5.2–5.4 of the report):

$$\tag{1} \frac{f_s}{f_{s,max}} = 0.96R^{0.33} \quad (0 \leq R \leq 0.5)$$

$$\tag{2} \frac{f_s}{f_{s,max}} = 0.86R^{0.16} \quad (0.5 \leq R \leq 3)$$

$$\tag{3} \frac{f_s}{f_{s,max}} = 1 \quad (3 \leq R)$$

$$\tag{4} R = \frac{z}{D} × 100$$

where,

$f_s$ = unit side resistance $f_{s,max}$ = ultimate unit side resistance, entered as the ultimate shear stress of the layer; the report compares the measured values with the FDOT design equation $0.5\sqrt{q_u}\sqrt{q_t}$ (Eq. 5.1, McVay et al., 1992) $z$ = vertical displacement of the shaft $D$ = shaft diameter

Joints, cracks and secondary structure in the rock may alter the behavior from the synthetic-rock curves.

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[McVay and Niraula, 2004] McVay, M. C. and Niraula, L. (2004). Development of P-Y Curves for Large Diameter Piles/Drilled Shafts in Limestone for FBPIER. Report BC354-59, Florida Department of Transportation, University of Florida, Gainesville, Chapter 5.