This EArly Grant for Exploratory Research (EAGER) award provides funding to test two hypotheses regarding the effect of dimensionless particle weight on maximum, minimum, and critical state void ratios. It has been established that van der Waals attractive forces between sand particles are approximately equal to the particle weights for very fine sands. For silt-sized particles van der Waals attractive forces can be much greater than the particle weight. The general hypothesis (Hypothesis 1) of this research is: if the attractive forces between soil particles are significant compared to the weight of the particles, the attractive forces will affect the densification and resultant void ratio of the particles. A more specific hypothesis (Hypothesis 2) is that the dimensionless particle weight, Wa = (particle weight)/(attractive force), can be used to characterize the importance of attractive forces with respect to their effect on void ratio and densification. These hypotheses will be tested by a series of experiments that vary the dimensionless particle weight while measuring the maximum, minimum and critical state void ratios of a selected idealized soil (glass spheres) and a real silica sand. The dimensionless weight due to van der Waals forces will be varied by 3 methods: changing the particle size, changing the pore fluid (air or water), and changing particle weight by spinning the soil in a geotechnical centrifuge.
If the general hypotheses (Hypothesis 1) is proven true, then the maximum and minimum void ratios (common ASTM index tests used to calculate the Relative Density of soil) measured in the laboratory in earth's gravity would not be directly applicable to soils in other g-fields (e.g., geotechnical centrifuge model tests). It follows that the Relative Densities reported for hundreds of valuable geotechnical centrifuge test programs may need to be corrected or re-interpreted. If the specific hypothesis (Hypothesis 2) proves correct, a method for correcting or performing the re-interpretation may be illuminated. This project's work on this aspect of particle size effects could reshape our general understanding of the effect of particle size on the strength and dilatancy of geomaterials; this understanding is of fundamental importance in design of foundations for buildings, bridges and other infrastructure.
