What are the two main causes of failure of hydraulic structure on the pervious foundation?

What are the two main causes of failure of hydraulic structure on the pervious foundation? Correct Answer Undermining and Uplift

Whenever a hydraulic structure is founded on a pervious foundation, it is subjected to seepage of water beneath the structure in addition to all other forces. The water seeping below endangers the stability of the structure and may cause its failure either by Piping or Undermining and Direct uplift.

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A hydraulic structure should not be built on pervious soil, because of _________