Description:

Modeling Failure in Earthen Structural Units

Abstract
The use of soil as a structural material dates back at least 10,000 years, and it is estimated that nearly one third of the world’s population lives in structure made primarily of earth. Earthen structures are also seeing renewed interest due to their sustainable nature, and the improvement of their properties through research.
The structural behavior of earthen structures, however, is still not completely understood. Earthen masonry, like all masonry, can fail in a variety of modes. However, because the mortar in earthen masonry is generally much closer to the strength of the bricks, a wider variety of modes are commonly seen in failure. The material may fail through diffuse plasticity, or fracture through the bricks and mortar, or at the weak interfaces. Propagating fractures can travel from the bulk brick to the interface and back again.
In this research, we create an enhanced finite element model of earthen structures to examine both diffuse and localized mechanical behavior. We use a modified cap plasticity model developed for geomaterials and fit to experimental data for the bulk data. The model is adapted for better tensile behavior, among other improvements.
To model propagating fractures, we use an enhanced strain finite element that allows for failure surfaces to be inserted at the critical orientation in the element, at a location consistent with the propagating fracture. Post-localization, a damage-like softening model that accounts for difference in tensile and shear strength. Failure on existing interfaces is governed by the same damage-like model, though with different material properties.
The model is applied to earthen structures both in-plane shear and out-of-plane bending. The results are compared to experimental data for simpler problems, and then some more sophisticated examples are run.

Bio
Craig Foster is an Associate Professor of Civil and Materials Engineering at the University of Illinois at Chicago. His research focuses on numerical modeling geomaterials and biomaterials. His research includes constitutive modeling, poromechanics, propagating fractures and other discontinuities.