Compression of granular materials

Compression data on over 100 sands were examined to clarify the role of particle rearrangement through interparticle slip and rotation and particle damage on primary compression, including the yield stress, secondary compression, and coefficient of lateral pressure at rest. During the increase in effective vertical stress, mechanisms such as tighter packing that promote particle locking and interparticle slip and particle damage that promote particle unlocking together determine the relationship between void ratio and effective vertical stress. Three levels of particle damage together with interparticle slip and rotation determine three types of compression behavior and a yield stress at the abrupt onset of particle fracturing and splitting. The ratio of secondary compression index to compression index is independent of whether compression results from overcoming interparticle friction through interparticle slip, from overcoming particle strength through particle damage, or both; and therefore it is a constant independent of the effective stress range. The coefficient of lateral pressure at rest of an initially dense sand starts with a value defined by the Jaky equation and the maximum friction angle and remains constant up to the abrupt onset of particle fracturing and splitting, at which point it begins to increase with an increase in effective vertical stress.