Numerical simulation of mechanical response of glacial tills under biaxial compression with the DEM

Glacial till deposits in the Greater Toronto Area (GTA) usually comprise fine-grained (clay and silt) and coarse-grained (sand, gravel, cobbles, and boulders) fractions, which are substantially heterogeneous in characteristics. Since coarse-grained fractions are too large to be tested in traditional laboratory equipment, the discrete element method (DEM) is applied in this study to simulate a series of large-scale biaxial tests to study the mechanical characterization of glacial till. This study is based on the results of comprehensive geotechnical investigations for the Eglinton Crosstown Light Rail Transit (LRT) Project in the GTA. The fine-grained till (clayey silt till) examined in this work is collected from the O’Connor Station site. The different proportions, gradations, and sizes of the coarse-grained fractions (gravel) with irregular random shapes and distributions are simulated. The analysis results indicate that the proportion of gravel influences the behavior and mechanical characterization of glacial till. The peak strength and initial modulus of the mixture gradually increase as the volumetric proportion of gravel increases to 30%. Beyond this percentage, the peak strength and initial modulus substantially increase. The failure mode of the sample changes from ductile to brittle with a volumetric proportion of gravel that is greater than 30%. In summary, when the volumetric proportion of gravel is limited to 30%, the gradation and size of the gravel only have a marginal influence on the mechanical characterization of the glacial till. However, a volumetric proportion of the gravel that exceeds 30% has significant impacts on the strength and deformation characteristics of glacial till.