Abstract
Coordination number controls elastic moduli, seismic velocity, and force transmission in sands and is thus a critical factor controlling the resistance of sands to deformation. Previous studies quantified relationships between coordination number, porosity, grain size, sphericity, and effective stress in pluviated or modeled sands. Here, we determine if these relationships hold in naturally-deposited beach sands. We collect samples while preserving their microstructures and use x-ray computed microtomography images to characterize grain properties. Similar to pluviated and modeled sand studies, we find that average coordination numbers and porosities for freshly deposited natural sands are 8.1 ± 2.8 and 0.37 ± 0.01, respectively. The range and standard deviation in coordination numbers of the natural beach sands are, however, significantly higher than observed in pluviated and modeled sand studies. At the same effective stress and porosities, coordination number is linearly proportional to grain surface area except for the smallest and largest grains. Coordination number depends non-linearly on sphericity. We attribute the higher ranges and standard deviations of coordination numbers in the natural sands to its broader grain size distribution, and we propose that the largest grains limit grain rearrangement, which influences spatial distributions of coordination numbers in natural sands.
Highlights
Coordination number is the number of grains in contact
An open question that we address is whether the same relationships exist in naturally-deposited sands. We answer this question by using x-ray computed microtomography to quantify relationships between coordination number, porosity, grain surface area, and sphericity in fresh and naturallydeposited sands at the Alameda County beach, Berkeley, California
Our results show that the average coordination numbers of these sands are roughly the same as predicted by existing pluviated and modeled sands studies but that naturally-deposited sands have higher variability in coordination numbers
Summary
Coordination number is the number of grains in contact. Coordination number affects the elastic moduli and seismic velocities of sands and is a critical parameter controlling how sand deforms. The coordination numbers of pluviated and modeled sands increase with decreasing porosity and increasing effective stresses [1,2,3,4,5] and decrease with decreasing sphericity [6]. An open question that we address is whether the same relationships exist in naturally-deposited sands We answer this question by using x-ray computed microtomography to quantify relationships between coordination number, porosity, grain surface area, and sphericity in fresh and naturallydeposited sands at the Alameda County beach, Berkeley, California. Our results show that the average coordination numbers of these sands are roughly the same as predicted by existing pluviated and modeled sands studies but that naturally-deposited sands have higher variability in coordination numbers. Additional studies in natural systems over a broader range of effective stresses and physical properties (e.g., grain contact area, angularity, and sorting) are needed
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
