Drilled Shaft IGM Non-Cohesive QZ (Mayne and Harris) [Mayne and Harris, 1993]

The base resistance of a socket in a Category 3 intermediate geomaterial follows the same socket load-settlement solution as the side resistance (Model 2 of [O'Neill et al., 1996], Eqs. 41–54).

Ultimate End Bearing

Undrained failure is assumed beneath the base, with the operational undrained strength correlated to the effective vertical stress at the base and the overconsolidation ratio:

$$\tag{1} s_u = 0.23\sigma'_{v0}OCR^{0.8}, \qquad OCR = \frac{0.2N_{60}p_a}{\sigma'_{v0}}$$

$$\tag{2} q_{max} = 9.33s_u$$

q-z Curve

The socket load-settlement relation is three-branched: elastic up to $Q_{t1}$ at settlement $w_{t1}$ (Eqs. 4–6 of the side-resistance page), then linear to the plunging load $Q_{t,max}$, then vertical. The base share of it is:

$$\tag{3} Q_{b1} = Q_{t1}-Q_{s,max}$$

$$\tag{4} Q_{t,max} = Q_{s,max}+q_{max}\frac{\pi D^2}{4}$$

$$\tag{5} \Delta w_b = (Q_{t,max}-Q_{t1})\frac{(1-\nu)(1+\nu)}{E_bD}$$

giving the q-z curve through (0, 0), ($w_{t1}$, $Q_{b1}$) and ($w_{t1}+Δw_b$, $q_{max}πD²/4$), constant beyond, where $E_b = E_{sL}/ξ$ is the modulus of the geomaterial beneath the base ($ξ$ = 2.5 for Piedmont residuum).

The Georgia Tech report of Mayne and Harris is not on file; the method is implemented from the FHWA report of O'Neill et al. (1996), which reproduces and revises it.

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[Mayne and Harris, 1993] Mayne, P. W. and Harris, D. E. (1993). Axial Load-Displacement Behavior of Drilled Shaft Foundations in Piedmont Residuum. FHWA Reference No. 41-30-2175, Georgia Tech Research Corporation, Atlanta. (Report not on file.)

[O'Neill et al., 1996] O'Neill, M. W., Townsend, F. C., Hassan, K. M., Buller, A., and Chan, P. S. (1996). Load Transfer for Drilled Shafts in Intermediate Geomaterials. Report FHWA-RD-95-172, Federal Highway Administration, McLean, VA.