Limestone Uncoupled (McVay) [McVay and Niraula, 2004]

This model uses the normalized Florida-limestone p-y trend line of [McVay and Niraula, 2004] that is corrected for the shaft side shear (Fig. 6.3 of the report), where $P/(D^{0.85}q_u^{0.15})$ is plotted against $y/D$. The correction removes the part of the back-computed lateral resistance that is actually supplied by the axial side shear along the shaft, which the report found to be about 25 % for a 6 ft shaft in 40 tsf rock. The report recommends these curves for conservative design when no separate moment-rotation springs are used. The version without the correction is Limestone (McVay).

The curve is piecewise linear with an initial slope, a secondary slope and an ultimate resistance:

$$\tag{1} p = 13750b^{0.85}q_u^{0.15}\Bigl(\frac{y}{b}\Bigr) \quad for \quad 0 < \frac{y}{b} < 0.004$$

$$\tag{2} p = b^{0.85}q_u^{0.15}\Bigl[1083\Bigl(\frac{y}{b}\Bigr)+51\Bigr] \quad for \quad 0.004 \leq \frac{y}{b} < 0.1$$

$$\tag{3} p = p_u = 159.3b^{0.85}q_u^{0.15} \quad for \quad \frac{y}{b} \geq 0.1$$

where,

$p$ = horizontal rock resistance per unit length (kips/ft) $q_u$ = unconfined compressive strength of the rock (ksf) $b$ = shaft diameter (ft) $y$ = horizontal displacement (ft)

The relationship is unit dependent (kips, feet, ksf). The report presents the trend line graphically (Fig. 6.3); the piecewise-linear coefficients above are the fit to that trend line.

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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.