Distinct Element Method for Study of Failure in Cohesive Particulate Media

Permissible stresses or strains in pavement layers constitute the empirical part of the mechanistic-empirical method. Whereas it appears to be possible to predict the actual stresses or strains under a load (the mechanistic part) reasonably correctly, there is much uncertainty with respect to the permissible values. Some of the possibilities that the distinct element method (DEM) raises for calculating permanent deformation and failure in pavement materials are explored. Because the study is limited to two dimensions and makes a number of assumptions that may not be strictly correct, the results should be considered as indicative of only some of the capabilities of DEM. After a brief description of DEM, tests to the failure of two different samples of elements are presented, with different element shape and size distribution and thus different resulting pore volume after compaction. For one of the samples, seven different stress paths were followed to failure (pure tension, uniaxial tension, pure shear, etc.). From this study, a nonlinear relationship between the permissible shear stress and the hydrostatic stress was deduced. Using this relationship as the basis for the kinetic equation in continuum damage mechanics can lead to cracking from the top of and the bottom of a slab. Finally, DEM is used to study the effect of repeated loading on permanent deformation and failure for one of the samples. The effect on permanent deformation was pronounced, whereas the effect on failure was much more uncertain, although there could be some indication of fatigue.