> 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-igm-cohesive-qz-oneill-et-al-1996.md).

# Drilled Shaft IGM Cohesive QZ (O'Neill) \[O'Neill et al., 1996]

Model 1 of \[O'Neill et al., 1996] for cohesive intermediate geomaterials (see the [side resistance](/technical-background/soil-structure-interaction/axial-soil-models/axial-tz-soil-models/drilled-shaft-igm-cohesive-tz-oneill-et-al-1996.md)) gives the base resistance of a socket as a power function of the settlement, derived from the finite element parametric study of the report and summarized in its formula sheet (Table 17):

$$
\tag{1}
q\_b = \Lambda w^{0.67}
$$

$$
\tag{2}
\Lambda = 0.0134E\_{m,tip}\frac{L/D}{L/D+1}\Biggl{\frac{200\Bigl\[\Bigl(\frac{L}{D}\Bigr)^{0.5}-\Omega\Bigr]\Bigl(1+\frac{L}{D}\Bigr)}{\pi L\Gamma}\Biggr}^{0.67}
$$

with $$Ω$$ and $$Γ$$ as defined for the side resistance:

$$
\tag{3}
\Omega = 1.14\Bigl(\frac{L}{D}\Bigr)^{0.5}-0.05\Bigl\[\Bigl(\frac{L}{D}\Bigr)^{0.5}-1\Bigr]\log\_{10}\Bigl(\frac{E\_c}{E\_m}\Bigr)-0.44, \qquad \Gamma = 0.37\Bigl(\frac{L}{D}\Bigr)^{0.5}-0.15\Bigl\[\Bigl(\frac{L}{D}\Bigr)^{0.5}-1\Bigr]\log\_{10}\Bigl(\frac{E\_c}{E\_m}\Bigr)+0.13
$$

where,

$$q\_b$$ = unit base resistance (kPa)\
$$w$$ = settlement of the base (m)\
$$E\_{m,tip}$$ = mass modulus of the IGM below the base (kPa)\
$$E\_m$$ = mass modulus of the IGM along the socket, $$E\_c$$ = modulus of the shaft concrete\
$$L$$, $$D$$ = socket length and diameter (m)

The relationship is unit dependent (kPa, m); OpenBrIM converts internally. It assumes a massive (not highly jointed) bearing material and carries no ultimate resistance; the curve is generated to a settlement of 3.5 in.

***

\[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.


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation by asking a question.

Perform an HTTP GET request on the following URL with the `ask` and `goal` query parameters:

```
GET https://docs.openbrim.org/technical-background/soil-structure-interaction/axial-soil-models/axial-qz-soil-models/drilled-shaft-igm-cohesive-qz-oneill-et-al-1996.md?ask=<question>&goal=<user_goal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is what the user is ultimately trying to achieve, the reason they need the answer. Sharing it helps GitBook give you a better, more relevant answer. A goal is most helpful when it describes the outcome the user wants rather than restating the question. For example, with `ask=how do I create an API token`, a goal like `automate deployments from our CI pipeline` lets GitBook tailor the answer to that use case.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.