Evolution of Nanomechanical and Macroscale Mechanical Responses of Expansive Clay during Swelling

Abstract

A controlled uniaxial swelling device is used to saturate sodium-montmorillonite (Na-MMT) clay samples and allow them to swell to various swelling levels. Nanomechanical experiments are conducted on the saturated samples at 0%, 10%, and 20% swelling levels to evaluate the force–displacement response, modulus of elasticity, and hardness and compare those values with those obtained for undisturbed dry clay. Unconfined compressive strength experiments are conducted to evaluate the undrained response for the swelling levels used in the nanomechanical experiments. The modulus of elasticity and hardness decreases with an increase in swelling but is higher than the dry clay. The clay particles also break down into smaller sizes with an increase in swelling. Swelling significantly impacts the unconfined compressive strength, nanomechanical properties, and microstructure of swelling clay. The mechanical properties of swelling clay at various length scales from macroscale to nanoscale and at different swelling levels are essential for the development of models to accurately predict the shear strength of swelling clay, critical for the economical and safe design of civil infrastructures.