# liquefaction.csr_driving()

Cyclic stress ratio applied by a hammer blow that fails the soil.

Usage

[Source](https://github.com/lornearnold/driven-pile/blob/main/src/driven_pile/liquefaction.py#L115-L129)

``` python
liquefaction.csr_driving(phi)
```

## Parameters

`phi: array_like`  
Friction angle, deg.

## Returns

`ndarray`  
`tau_max / sigma'v0 = (1 - sin phi) tan phi`.