Strength ratio, pore pressure parameter and effective stress change

Pore pressure development in undrained loading, and ratio of undrained strength to initial effective stresses can be linked to the geometry of the undrained effective stress path. This geometry can be characterised in a fundamental way by the ratio of initial to final mean effective stresses. Although values of this ratio can in principle be estimated using an elastic-plastic soil model such as Cam clay, the variation with angle of shearing resistance or plasticity thus estimated does not correspond with field observation