Date of Graduation


Document Type


Degree Name

Bachelor of Science in Civil Engineering

Degree Level



Civil Engineering


Bernhardt, Michelle L


The discrete element method (DEM) has been used extensively to study soil, rock, and masonry behavior because of its ability to model the materials as individual particles or bonded clumps of particles. DEM allows for examination of the macro- and micro-scale response and provides a means to study the fundamental material behavior, but it is still considered computationally expensive in relation to other methods. To lower computational costs, the smallest particle sizes are often considered negligible and are left out of the model. Additionally, rock or intact materials are often modeled as a bonded assembly of uniform spheres. To date, few research studies have considered the influence of particle size and gradation on the strength and fracture behavior of bonded assemblies. This research aims to examine the influence of particle gradation in bonded assemblies through laboratory calibrated DEM simulations. Additionally, the role of the cement-sized particles will also be investigated. While the overall motivation for this study is related to the behavior of mortar in historic preservation applications, the preliminary studies can be directly applied to other geo-related materials such as cemented sands and rock specimens. This study addresses two critical questions associated with the computational efficiency of bonded assembly models (1) Does particle gradation influence the overall strength and fracture behavior, and (2) Do the smallest size particles influence the overall results enough to justify the additional computational cost? In this study two mortar materials, varying only in sand particle gradation, are subjected to physical laboratory compression strength tests to assess whether or not the influence is observed in physical experiments. Additionally, the compression test results act as a means of calibrating the simulations in DEM. These simulations will examine the macro- and micro-scale influence of particle gradation on the strength of bonded assemblies. Additional simulations are used to examine the effects of modeling the cement-sized particles in the bonded assembly. The results of the physical experiments and the development of the DEM simulations are discussed herein.