The purpose of this dissertation is to contribute to the detection of the onset of geomechanical instabilities in sands under dry/drained and saturated/undrained conditions. ln order to accomplish this objective, a framework for detecting instabilities based on either a mathematical concept (i.e., loss of uniqueness - bifurcation) or physical one (i.e., Hill 's instability) is generated to derived criteria applicable to the most common instabilit...