# bearing.nq_vesic()

Vesic bearing capacity factor on vertical effective stress.

Usage

[Source](https://github.com/lornearnold/driven-pile/blob/main/src/driven_pile/bearing.py#L14-L47)

``` python
bearing.nq_vesic(
    phi,
    irr,
    k0=None,
)
```

## Parameters

`phi: array_like`  
Friction angle, deg.

`irr: array_like`  
Reduced rigidity index.

`k0: array_like = None`  
At-rest earth pressure coefficient; `1 - sin(phi)` by default.

## Returns

`ndarray`  
`N_q* = N_sigma (1 + 2 K0) / 3` with `N_sigma = 3 / (3 - sin phi) exp((pi/2 - phi) tan phi) tan^2(45 + phi/2) Irr^(4 sin phi / (3 (1 + sin phi)))`.

## References

Vesic (1977).