The CUSTOM SRD method has been implemented to base the SRD directly upon the calculated axial capacity within OPILE. As such it can only be used when axial capacity calculation output is present.
For compatibility the CUSTOM SRD method also forces the SRD pile grid to be the same as the pile grid used for axial capacity, as such, the CUSTOM SRD method is based on the Axial Pile Grid.
In order to use the CUSTOM SRD method it is only necessary to fill in a series of factors on the skin friction and end bearing and select from the option of plugged or unplugged. No other specific SRD input is required for the CUSTOM method.
An example of the CUSTOM SRD table is shown below.
Skin friction is taken as the external skin friction as calculated in the axial capacity table. To derive the SRD, the skin friction is factored using the skin friction factors as entered in the custom SRD table. Separate factors are allowed for sands and clays.
Note that for SRD full external and internal skin friction would be derived by using a skin friction factor of 2.0. A skin friction factor of 1.0 could either mean external friction only, or some other combination of external and internal friction (e.g. 50% external, 50% internal); a factor of 1.2 could be used if it were intended to use 70% of external friction and only 50% of internal friction.
Care should be taken for selection of factors in combination with the end bearing state selected.
End bearing is taken as the end bearing pressure calculated in the axial capacity table. Note, that in the axial capacity table the “unplugged end bearing capacity” in kN includes annular end bearing and internal skin friction, depending upon the axial method selected.
To avoid complications the unplugged and plugged end bearing pressures are taken and are then multiplied by the annular or full end bearing areas are required.
The option of using plugged or unplugged end bearing is offered in OPILE. In order to use either it is essential that the axial capacity calculation has output continuous values for both, otherwise the results may not be meaningful. Some methods, such as CLAYICP, may not output continuous values of unplugged or plugged end bearing.