> For the complete documentation index, see [llms.txt](https://docs.openbrim.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.openbrim.org/technical-background/soil-structure-interaction/lateral-soil-models/limestone-uncoupled-mcvay-mcvay-and-niraula-2004.md).

# 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)](/technical-background/soil-structure-interaction/lateral-soil-models/limestone-mcvay-mcvay-and-niraula-2004.md).

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.

***

\[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.


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