Calculation of speed and

velocity discontinuity's length:

The curved failure mechanism was constructed according to the theory that the energy dissipation rate and external work rate were calculated along the velocity discontinuity [25].

S is the length of velocity discontinuity, [X.sub.i] is the body strength which is caused by weight, V is the volume of the plastic zone, and [v.sub.i] is the velocity along the velocity discontinuity surface.

Therefore the work rate produced by seepage forces along the velocity discontinuity surface is

A disadvantage of the application of these solutions to the process of extrusion is that they do not account for the power dissipation at velocity discontinuity surfaces.

In order for the velocity field (4) to be compatible with the motion of rigid zones 1 and 2 (Figure 1), it is necessary to introduce velocity discontinuity lines through points A and B.

In the numerical analysis literature, a velocity discontinuity point is called a breaking point [8], while in variational calculus (and here) the name corner point is used [5].

Should the extremal trajectory of particle i have a velocity discontinuity at time [t.sub.i], the trajectory of particle j must compensate with a corner point in light-cone at either [t.sub.j-] or [t.sub.j+], in order to make the right-hand-side of (16) continuous.

This means that the dispersion data requires a pronounced velocity discontinuity at a depth of about 400 m.

[FIGURE 7 OMITTED] @@ From the viewpoint of the geological structure of the area it seems that the velocity discontinuity at an approximate depth of 400 m probably corresponds to facial boundary having a smooth transition between the Hradec greywacke and Kyjovice shale, which consist of rocks with different petrographical composition.

According to the normality condition for an associated flow rule Coulomb material, for a kinematically admissible failure mechanism, the velocity discontinuity along a plastically deformed surface must make an angle <p with this velocity discontinuity surface [17].

Considering that the mechanism is rigid, the only source of energy dissipation is derived from the plastic soil deformation that occurs along the velocity discontinuity surface.