Undrained shear strength

Hey guys, how can I set a undrained shear strength of saturated sand by using the Mohr Coulomb model, like described in the figure? I understand that if no limit for shear is assigned and the confining pressure is great enough, then no shear failure of soil will be observed. However, the shear failure depends mainly on the difference of sigma_1 and sigma_3.

Just assign undrained properties, e.g., friction = 0, cohesion = Cu.

Does that mean there is no failure criteria dscribed by the inclined dashed line (tau=c*tan(phi)+sigma) for saturated sand? Because no friction between the sand particles will occur, when the sand is saturated.

That is for undrained total stress approach.
Actually, undrained calculation has several options (dry or wet approaches). In dry approach, there are effective or total stress methods. It is detailed in the section: