Granular Materials in Civil Engineering: Recent Advances in the Physics of Their Mechanical Behavior and Applications to Engineering Works - Multiscale Geomechanics: From Soil to Engineering Projects - page 46

reduces the apparent friction. As a consequence, the maximum strength envelope is
no longer a straight line but has a curvature with a reduced slope when the stresses
increase, which can be fitted by a power law with a coefficient equal to 0.77.
Figure 3.5. Shear strength envelope for “reduced” basalt rockfill
3.1.3.4. Other experimental validations
Other validations of the dissipation equation [3.10] were made for different
experimental conditions, including the plane strain condition with rotation of the
loading directions, and large-amplitude cyclic loading in a true triaxial apparatus
[FRO 86].
These experimental results, in particular, provide access to the internal feedback
rate, R , which takes the following values:
− between 0.05 and 0.20 according to grain angularity, roughness and elongation
in triaxial compression tests;
− between 0.15 and 0.30 according to grain angularity, roughness and elongation
in plane strain condition.
3.1.3.5. Failure criterion at critical state
At critical state, the failure criterion corresponding to the dissipation equation is
obtained by introducing the condition of constant volume into equation [3.10].