Pile group in multilayered Soil

[pu_connect]

If a pile group passes through a sand layer and rests on a clay layer, then do we need to check against pile group failure?
Related question: Say a group of pile passes mostly through clay and has bearing on sand layer, then do we need to do group failuren check?

[rodsalgado]

If a pile group passes through a sand layer and rests on a clay layer, then do we need to check against pile group failure?
Related question: Say a group of pile passes mostly through clay and has bearing on sand layer, then do we need to do group failuren check?

Conceptually, we should check every limit state we believe to be possible. However, your question touches on the likelihood of these limit states. An axial group bearing in dense sand, for example, is very unlikely to experience bearing capacity failure. The other case you mention is more likely but still not among those that would be consider probable. We should not prejudge and always consider the specifics of the problem before ruling out a limit state.