Amp. Wedage et al., A STRAIN-RATE DEPENDENT CONSTITUTIVE MODEL FOR CLAYS AT RESIDUAL STRENGTH, Canadian geotechnical journal (Print), 35(2), 1998, pp. 364-373
Plasticity theory is extended to incorporate strain rate effects on th
e residual shear strength of clays. The clay is assumed to behave elas
tically before yielding and then in a perfectly plastic manner with no
volume change during yielding. The Mohr-Coulomb failure criterion is
used in the rate-dependent model in which the strain rate affects the
mobilized effective friction angle of the material. During initial yie
lding and subsequent plastic deformation, the stress and strain states
at a point will satisfy I:he rate-dependent yield function (loading f
unction). When the effective plastic strain rate decreases to a thresh
old strain valuer the loading surface moves, or collapses, to the stat
ic yield surface. A constant volume flow rule is used to calculate pla
stic deformation. The computed stress-strain relationship is formulate
d in two parts, namely a rate-independent part and a rate-dependent pa
rt. The rate-independent part is the same as that used in classical el
astoplastic formulations, whereas the rate-dependent part is dependent
on the current strain rate of the material. The use of the model is i
llustrated using a numerical example simulating a two-dimensional plan
e strain test.