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7MAKECAVITYPLACESTONE ATBOTTOM OFCAVITYRAM STONETO FORMBOTTOMBULBDENSIFYSTONE INLIFTS ANDPRELOADFigure 2: Simplified aggregate pier installation procedure (reproduced per Fox et al.,2004)Uncemented aggregate piers typically deform by bulging or tip movement. Bulgingdeformation typically develops in longer piers or where the bulb is supported by a stifferlayer of soil. Pier bulging is supplemented with lateral displacement in the adjacent matrixsoil, which is typically observed to occur within the top portion of the pier (Wissmann,1999). The lateral confinement provided by the matrix soil controls the amount of soil lateraldisplacement and has been proven to correlate with the amount of settlement that theaggregate pier undergos (Handy, 2001).However, the mechanism of aggregate pier punching failure can also be developed whenstresses at the pier bottom are high. As the length of the aggregate pier decreases, the piertends to act more as a solid structural element and undergo less internal deformation.Therefore, shorter length aggregate piers are less vulnerable to settle through process ofbulging and more inclined to undergo shearing deformation at the tip of the aggregate pierelement by process of plunging (White and Suleiman, 2004). Additional to the failure at thetip, aggregate pier skin friction is mobilized on the interface of pier shaft (White andSuleiman, 2004). However, unlike other types of supporting systems (for example piles),aggregate pier construction is not limited by the presence of a better layer of firm soil at apier tip. The additional amount of confinement at the tip of the aggregate pier is first