The role of particle breakage in the mechanics of a non-plastic silty sand

A detailed investigation was carried out on a silty sand from Boštanj, Slovenia, in order to identify the role that particle breakage plays in test interpretations and mechanics. The soil was tested up to a high pressure in the triaxial and oedometer apparatus. Unexpected for a silty sand, the basic patterns of behaviour, in terms of strength and stiffness, were found to be similar to those of many previously investigated clean sands, with unique and parallel Normal Compression and Critical State Lines at higher stress levels and a horizontal asymptote to the Critical State Line at lower stress levels. The stiffness was controlled primarily by the state of the soil relative to the location of these lines. Despite the better grading, there was still very significant particle breakage. However, the breakage was largely confined to the coarse fraction. The grading curves after various tests all showed convergence with the initial grading towards 1 μm, which may therefore represent the comminution limit. It is believed that it is the particle breakage that caused the behaviour to follow a simple Critical State type of framework and why transitional or non-convergent compression behaviour was not found.