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

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

\[Aurora and Reese, 1976] loaded four instrumented drilled shafts to failure in clay-shale at two Texas sites (Montopolis and Dallas). The shafts were under 30 ft long and penetrated about 5 ft into the clay-shale; the peak load transfer was mobilized at movements of 1/4 in or less, and the construction method governed the capacity. The design conclusions of Chapter 9 give the side resistance as an $$α$$-method:

$$
\tag{1}
t\_u = \alpha c\_Q
$$

where,

$$t\_u$$ = ultimate unit side resistance\
$$c\_Q$$ = shear strength of the clay-shale from a quick triaxial test with confining pressure about equal to the effective overburden pressure\
$$α$$ = shear strength reduction factor: 0.5 for the slurry displacement or casing method, 0.75 for the dry method

Where only dynamic penetration data are available, the report suggests, with caution, $$c\_Q$$ (tsf) = $$N\_{THD}$$/75 for the Texas cone penetrometer (Eq. 9.2).

### t-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-tz-soil-models/drilled-shaft-clay-tz-reese-and-oneill-oneil-et-al.-1999.md) model of \[O'Neil et al., 1999], with $$t\_u$$ from Eq. (1) ($$Z = z/D × 100$$):

$$
\tag{2}
t = t\_u(4.92Z) \ (Z \leq 0.12), \qquad t = t\_u\frac{Z}{0.0951+0.893Z} \ (0.12 < Z \leq 0.74), \qquad t = t\_u(0.9789-0.1158(Z-0.74)) \ (0.74 < Z \leq 2.0), \qquad t = 0.833t\_u \ (Z > 2.0)
$$

The recommendations apply to shafts with the geometry of the tests and to clay-shales with quick-triaxial strength below 10 tsf.

***

\[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. (Summarized in Aurora and Reese, 1977, *Proc. 9th ICSMFE*, Tokyo, 371–376.)


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