CONTACT LAWS FOR CEMENTED GRAINS - IMPLICATIONS FOR GRAIN AND CEMENT FAILURE

Analytical solutions are presented to predict the intergranular contact load transfer in cemented granular media where both grain material and cement are elastic. The grains can be separated, have a direct point contact, or be compacted prior to cement deposition. For all these cases contact stress distributions are obtained for normal, tangential and torsional deformation of two cemented deformable grains. An important result is that intergranular cement: even if very soft, is load-bearing. Thus cementation reduces contact stress concentration (as compared with direct Hertzian interaction). Contact stresses are maximum near the center of the contact region when the cement is soft relative to the grains, and are maximum at the periphery of the contact region when the cement is stiff. These results allow us to predict the Following modes of static and dynamic failure of the grains and intergranular bonds in a particulate material. (1) Uncemented grains will tend to shatter whereas cemented grains will stay intact, and the cement will fail. (This conclusion is supported by hydrostatic loading experiments where intensive crushing of uncemented glass beads was observed at about 50 MPa, whereas grains cemented at their contacts with small amounts of epoxy stayed intact.) (2) Where intergranular cementation is present, grain failure may still be expected if the cement is strong and stiff. In this case, grain damage will be initiated at the periphery of the cement layer. (3) Yielding of a cement material that is soft (as compared with the grain material) will initiate at the center of the contact region, whereas stiff cement will yield at the periphery.