An important parameter used to predict the bearing capacity of a single stone column is the internal friction angle of the aggregate. Typically, constant friction angles are used to design stone columns regardless of the effects that particle shape, gradation, and aggregate-matrix soil interaction may have on the global performance of the pier. Because the bulging failure mechanism normally controls the global performance of single stone columns with L/D ratio greater than 4, a significant reduction in the internal friction angle could occur due to an increase in the confining pressure at the bulging zone during the load application. To examine this phenomenon, full-scale 3D discrete element method (DEM) simulations were developed to replicate field plate load tests on spread small circular foundations (0.76 m) supported on isolated stone columns in order to determine the corresponding load-displacement curves. The results demonstrate that incorporating a variation in the friction angle in the DEM models which is dependent on the level of confining pressure provides a better numerical representation of the load-displacement curve obtained from the field.
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