Micro-Scale Characterization of Quartzitic and Carbonate Sand Grains Using Nanoindentation

Abstract

Many offshore energy infrastructures are built on carbonate sands which are skeletal remains of marine organisms. Carbonate sands have a porous grain structure and are more compressible compared to quartzitic sand grains which are abundant in alluvial depositional environments. Consequently, there is a stark difference in material behavior of carbonate sands and it is difficult to characterize this distinct behavior with conventional methods. This study focuses on micro-scale characterization of carbonate and quartzitic sands to overcome this challenge. Experimental studies consist of nanoindentation tests performed on 17 different sands; 7 quartzitic and 10 carbonate sand samples. Mechanical properties of individual sand grains with different mineralogies are determined using nanoindentation. A force is applied by the nanoindenter on the grain surface and the load-displacement curve is developed. Modulus and hardness of individual sand grains are evaluated. Nanoindentation test results show that modulus and hardness of carbonate sands are significantly lower than quartzitic sands. For quartzitic grains, mechanical properties are relatively independent of indentation depth; whereas, for carbonate grains there is a considerable decrease in both Young's modulus and hardness values with increasing indentation depth. Results from this study can further be used for the evaluation of compressibility and strength characteristics of these two types of sands as part of a multi-scale analysis framework.