The evolution of crushing in granular materials and its influence on their mechanical properties

University Of Pittsburgh, Pittsburgh PA

Investigators

Abstract

Granular materials forming part of the base of flexible pavements, rockfills, highway embankments, and foundations experience crushing as a result of static and dynamic loads. Very little is known about the effect that varying levels of crushing have on the engineering properties of granular materials (i.e. hydraulic conductivity, shear strength, and elastic moduli). Because of sustained crushing, the original engineering properties with which a structure (i.e. a pavement's granular base or a highway embankment) was designed will change during its engineering life. Changes in the original engineering properties could affect the stability of the structure and could make it unsafe. Thus, there is a need to understand the evolution and the mechanics of crushing in granular materials. To this effect we will: (1) conduct laboratory and simulation investigations on the evolution of crushing in granular materials. The laboratory investigation will involve tests that induce crushing in granular materials (static and dynamic compression and shear tests). The evolution of crushing in these tests will be evaluated by assessing the micro-structural changes that take place in the samples and by comparing the grain size distribution of the materials measured before and after the crushing tests. Also, the Discrete Element Method (DEM) will be used to study the level and distribution of the interparticle forces that cause crushing; and, (2) evaluate the changes in engineering properties caused by the crushing process. The engineering properties that will be evaluated before and after crushing are: hydraulic conductivity, shear strength, and the elastic moduli of the granular materials tested. The results of the research will be valuable to the geotechnical engineering community, for the better design of civil engineering structures such as flexible pavements and for a better understanding of the ways the stability and settlement experienced by highway embankments evolve as a result of crushing.