> 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/axial-soil-models/axial-qz-soil-models/drilled-shaft-clay-shale-qz-aurora-and-reese-aurora-and-reese-1976.md).

# Drilled Shaft Clay-Shale QZ (Aurora and Reese) \[Aurora and Reese, 1976]

From the field tests described for the [side resistance](/technical-background/soil-structure-interaction/axial-soil-models/axial-tz-soil-models/drilled-shaft-clay-shale-tz-aurora-and-reese-aurora-and-reese-1976.md), \[Aurora and Reese, 1976] measured ultimate base resistances of 53.5 to 64.0 tsf at Montopolis and 25.5 tsf at Dallas, considerably higher than the values then adopted for design. The design conclusions of Chapter 9 give the unit base resistance as:

$$
\tag{1}
q\_u = N\_cc\_Q \leq 40 \ tsf
$$

where,

$$q\_u$$ = ultimate unit base resistance\
$$c\_Q$$ = quick-triaxial shear strength of the clay-shale below the base\
$$N\_c$$ = bearing capacity factor: 7.0 for the slurry displacement method, 8.0 for the casing or dry method (judged conservative given the limited data)

The 40 tsf cap is not in the report, whose own tests reached 53.5 to 64.0 tsf at Montopolis; it is the limit of the [Drilled Shaft Clay](/technical-background/soil-structure-interaction/axial-soil-models/axial-qz-soil-models/drilled-shaft-clay-qz-reese-and-oneill-oneil-et-al.-1999.md) model whose load-transfer curve is borrowed below, and it is kept as a conservative design bound. Where only penetration data are available, the report suggests with caution $$q$$ (tsf) = $$N\_{THD}$$/10 (Eq. 9.1).

### q-z Curve

The report does not propose a load-transfer shape. OpenBrIM therefore applies the normalized curve of the [Drilled Shaft Clay](/technical-background/soil-structure-interaction/axial-soil-models/axial-qz-soil-models/drilled-shaft-clay-qz-reese-and-oneill-oneil-et-al.-1999.md) model of \[O'Neil et al., 1999], with $$q\_u$$ from Eq. (1) ($$Z = z/D × 100$$):

$$
\tag{2}
q = q\_u(0.00011823Z^5-0.0037091Z^4+0.044944Z^3-0.26537Z^2+0.78436Z) \ (Z \leq 6.5), \qquad q = 0.98q\_u \ (Z > 6.5)
$$

***

\[Aurora and Reese, 1976] Aurora, R. P. and Reese, L. C. (1976). *Behavior of Axially Loaded Drilled Shafts in Clay-Shales.* Research Report 176-4, Center for Highway Research, The University of Texas at Austin.


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