Subbase degradation: permeability and strength reductions by means of breakage soil mechanics
While subbase is often the main load-bearing layer of pavements, there is a severe lack of understanding of the fundamental physical effects that govern the gravel constitutive behaviour (i.e., the behaviour in terms of stresses and strains). While the subbase is usually made out of crushed stones or slags, the weakness of this material is understood to relate to the individual particles – typically being angular and usually containing pre-existing flows coming from the extreme conditions imposed during the industrial creation process. As a result, there is also an appreciation to the fact that the subbase material should be vulnerable and prone to further crushing if future loads from the overlaying base-course layer are introduced. As the average grain size reduces, so does the permeability, a problem that sets a real challenge for the engineers in designing adequate drainage systems. A further material degradation that the size reduction causes is the strength reduction.
How exactly should grain crushing be introduced to model permeability and strength reductions is an open question. The answer of this question will be the primary objective of this PhD research, which will focus on applying the theory of Breakage mechanics and the use of experiments to validate the theory.