Mechanical and Civil Engineering Seminar

Mechanical and Civil Engineering Seminar Series

Title: Unveiling the Failure of the Effective Stress Theory in Unsaturated Materials: A multiscale journey using DEM

Abstract: The Effective Stress Principle (ESP) stands as one of the most renowned and fundamental theories in soil mechanics and geotechnical engineering. Attributed to Karl Terzaghi in the early 20th century, the ESP was developed to understand the mechanical behavior of soils whose pores are fully filled with water (saturated soils). Since then, the ESP has become a cornerstone theory in the field; robust and simple, it seemed natural to try to extend it to soils where both water and air occupy the pores (unsaturated soils). Over more than 70 years, researchers have tried to generalize the notion of effective stress to all types of soils. To date, no one has fully succeeded. Only recently, by means of discreteelement modeling (DEM), several works have suggested that the ESP can still be applied to unsaturated soils. In this seminar, these works are discussed and tested under realistic material conditions. Using DEM simulations, we model wet granular assemblies subjected to triaxial shearing tests. Different from previous works, we consider different particle size distributions, ranging from uniform to high polydisperse, and contact interactions that mimic pendular water bridges as measured experimentally. Through a series of macroscopic and microstructural analyses, we unveil a series of underlying factors that invalidate the recent ESP approaches to describe the shear strength of unsaturated soils. This work also provides insights into potential avenues to fix and generalize the ESP for unsaturated materials based on the contact and force networks of solid contact interactions and capillary interactions.

Bio: David is a civil and geotechnical engineer from the Universidad de los Andes in Colombia, who conducts research on granular physics and geomechanics using mathematical modeling and numerical simulations. He obtained his Ph.D. from the Université de Montpellier in France and has been involved in international collaborations between academic institutions in France and Thailand. He currently serves as a Research Associate at Polytechnique Montreal, Canada. Among his research works, he has developed discrete and finite element models to investigate the impacts of grain shape and particle size distribution on the shear strength of geomaterials, studied the influence of grain crushing and deformability on the compaction of diverse materials - ranging from powders to rubbers - and explored the scaling effects of sample size on mechanical properties. His research also covers the effects of water in geomaterials, with a focus on exploring the fundamental laws behind the mechanics of unsaturated granular materials.

NOTE: At this time, in-person Mechanical and Civil Engineering Lectures are open to all Caltech students/staff/faculty/visitors.