critical time step

Dear all,

I have a problem regarding critical initial time step in poroelastic material during consolidation process.

正如我们所知,隐式integration method, it's unconditionally stable. But for the consolidation of poroelastic material,

there is a critical time step t_critical derived by Vermeer and Verruijt (1981), this has also been inclued in the abaqus software (http://129.25.22.58:2180/v6.7/books/exa/default.htm).