that two-wave structures exist for 23.7 ≤ up ≤ 53.4m/s
for φL = 0.90; steady viscoelastic waves are predicted for
up < 23.7m/s,whereas steadywaves having viscoelastic and
viscoplastic components are predicted for up > 53.4m/s.As
with the simulation shown in Fig. 4, the interaction of the
incident wave with the initially loose material results in a
backward propagating release wave and a forward propagating
transmitted wave. The release wave here, however,
is slightly more complex owing to the transient interaction
of the incident two-wave structure with the loose material