The study shows that both generalized shear stress and the first invariant function of stress tensor become smaller and smaller when pore pressure increases during the course of the development of sand boil.

In this paper elastoplastic stress analyses for thick-walled tube and sphere shell with different strength in tension and compression are conducted using the theory of generalized twin shear stress strength.

As an example, two limit criteria of generalized square principal stress are proposed.

Considering the effect of hydrostatic pressure and intermediate principal stress,the generalized twin shear stress yield criterion,and the associated normal flow rule are used in the plastic stage.

A fuzzy reliability calculating model is given again based on function which includes generalized stress and generalized strength.

Based on the similar equations of the elastic-plastic model theory and the plastic deformation theory,this paper presents,according to the plastic model theory and the relations between generalized stress σi and strain εi curves of prototype materials,the resilience test model of elastoplastic stress analysis with .