# Colliat¶

The Colliat method for calculating SRD is implemented based upon Colliat et al (1993) and Puech et al (1990). The method was developed primarily for use in hard clays and is implemented in the same way as the stevens_ method with the exception that the skin friction in clays is modified to account for a residual effect.

Note

It should be noted that the Colliat et al (1993) paper published information that superseded Puech et al (1990), although both papers will need to be consulted to understand the application of the method.

For the Colliat method the shaft friction in clays is calculated very similarly to the CLAYAPICOMM_ axial method, however it is then factored by a factor Fp which is defined by:

$F_p = \lambda \cdot OCR^{0.3}$

Where:

 $$\lambda$$ an empirical factor depending on the distance to the pile tip and whether the calculated value is upper or lower bound (see below). $$OCR$$ is the overconsolidation ratio (see Stevens_ for the use of OCR/plasticity index).

In addition to those inputs required for the Stevens_ method Colliat requires the following:

• Upper bound residual lambda: taken as 0.25;

• Lower bound residual lambda, taken as 0.05;

• Upper bound lambda maximum, taken as 0.5;

• Lower bound lambda maximum, taken as 0.2;

• A non degradation length: i.e. the distance, measured from the pile tip, over which the maximum lambda values are applied.

Colliat et al suggest to use a A non degradation length of 10m and this is also the default value in OPILE. The upper and lower bound lambda values are used for the upper and lower bound SRD predictions, respectively.

If the distance above the pile tip is more than the degradation length then the residual value of lambda is used. If the distance above the pile tip is less than the degradation length then the maximum lambda value is used. The figure below shows how the various lambda values are implemented.