Different pile shear stiffness in compression vs tension

[Samuel]

Hi everyone,

I would like to propose a feature enhancement for pile members in RFEM 6 geotechnical analysis (or check if it there is a workaround to accomplish it).

At present, pile resistance parameters such as shaft resistance / skin friction are defined using a single set of values. From what I can see, there is no direct way to define different shaft resistance parameters for compression and tension within one model. The only workaround I am aware of is to use two separate models: one model containing only compression load cases with compression-based pile resistance values, and a second model containing only tension (uplift) load cases with reduced pile resistance values. If there is a simpler or more direct workaround within RFEM 6, I would appreciate confirmation.

The motivation for this request is that shaft resistance is direction-dependent in real soils. In geotechnical practice, it is common for site investigation reports to specify different shaft resistance values for piles in compression and in tension. Uplift shaft resistance is typically lower than compression resistance due to soil unloading, reduced effective stress, and interface slip effects at the pile–soil boundary. Load testing and published research regularly show that tension shaft resistance may be 60–80 percent of the compression value, depending on soil type and installation method. Using a single resistance value for both directions can therefore be unconservative for uplift or overly conservative for compression, depending on how it is calibrated.

I have been using the dlubal reference below to help me with my modelling of the piles in the geotechnical analysis add-on.
https://www.dlubal.com/en/support-and-learning/support/knowledge-base/001924

It would be very helpful if future versions of RFEM allowed separate shaft resistance parameters for compression and tension within the same pile definition, or an equivalent mechanism that automatically applies different resistance values based on force direction.

Thanks in advance, and I would be interested to hear how others are currently handling this.

[juliane.stopper]

@Samuel

Uplift shaft resistance is typically lower than compression resistance due to soil unloading, reduced effective stress, and interface slip effects at the pile–soil boundary. Load testing and published research regularly show that tension shaft resistance may be 60–80 percent of the compression value, depending on soil type and installation method. Using a single resistance value for both directions can therefore be unconservative for uplift or overly conservative for compression, depending on how it is calibrated.

Thanks a lot for your post!

We understand your request for an option to consider different pile resistances depending on tension and compression. We’ll discuss this requirement internally with our team.

As soon as such an option becomes available, we’ll make sure to inform you via our update reports.

Thanks again for your valuable input and for helping us improve our software!