Modeling of Degradation and Failure of Earthen Structural Units

Abstract

Soil is one of the oldest materials humans have used to build their dwellings and other structures. Almost universally available, easily shaped, highly sustainable, possessing high thermal mass, and easily recyclable, earthen materials are highly sustainable and often a natural choice. Improperly designed, however, earthen structures are subject to erosion, earthquakes, and other types of extreme loading. They may fail in a sudden and brittle manner as well if not properly detailed. We examine the behavior of modern earthen structural elements under shear loading. Cement-stabilized soil block, or compressed earth block, and stabilized rammed earth are used in the number of locations worldwide. In addition to their sustainability, they are cost-effective in many locations. These materials are often stabilized with a small amount of cement for strength and durability. We analyze wall units using a finite element model with embedded strong discontinuities. The bulk material model is a plasticity model that includes both tension and compression caps, a pressure-dependent shear yield surface, differences in triaxial extension and compression strength, isotropic cap hardening, and kinematic shear hardening/softening. The tensile and shear cohesion degradation under large deformation can be modeled. In addition, on detection of localization, an interface may be inserted or activated at the critical orientation. The elements have been extended to include preexisting weak interfaces, such as those between layers of rammed earth, or brick and mortar joints. However, interfaces can also be extended through the bulk material if that path is more critical for a given stress state.