> 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/driven-pile-clay-tz-coyle-and-reese-coyle-and-reese-1966.md).

# Driven Pile Clay TZ (Coyle and Reese) \[Coyle and Reese, 1966]

From laboratory tests and full-scale field tests on instrumented steel friction piles in clay, \[Coyle and Reese, 1966] correlated the load transferred to the soil with the pile movement and presented the load-transfer ratio as a function of displacement:

| $$z$$ (in) | 0.00 | 0.01 | 0.02 | 0.04 | 0.06 | 0.08 | ∞    |
| ---------- | ---- | ---- | ---- | ---- | ---- | ---- | ---- |
| $$t/t\_u$$ | 0.00 | 0.18 | 0.38 | 0.79 | 0.97 | 1.00 | 1.00 |

where,

$$t$$ = unit side resistance (skin friction)\
$$t\_u$$ = ultimate (nominal) unit side resistance, entered as the ultimate shear stress of the layer\
$$z$$ = vertical displacement of the pile

A very small displacement, under 0.1 in, mobilizes the full side resistance.

{% hint style="info" %}
The journal article is not yet on file, so the table is implemented as it is reported in the secondary literature; it will be checked against \[Coyle and Reese, 1966] once the original is obtained. API RP 2A-WSD (2007), Section 6.7.2, also refers to this work for *t-z* curves in clay.
{% endhint %}

***

\[Coyle and Reese, 1966] Coyle, H. M. and Reese, L. C. (1966). Load transfer for axially loaded piles in clay. *Journal of the Soil Mechanics and Foundations Division*, ASCE, 92(SM2):1–26. (Article not on file.)


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