Densified aggregate piers have been widely used for ground improvement since the mid 1990's. The piers are typically constructed by backfilling cylindrical cavities with densified stone using a vertical ramming apparatus. The strength and compressibility of densified aggregate piers systems are confining stress dependent and tend to have low capacities in highly compressible soil because of their tendency to bulge into weak soil. This paper describes the design and construction of a densified aggregate pier system with polymeric shells for confinement in soft soil for a highway embankment in Seeley's Bay, Ontario, Canada. The method allows for the insertion of high density polyethylene (HDPE) sleeves into the ground through the soft materials using a specially adapted mandrel. This paper is of particular significance because it presents significant insight into an effective ground improvement method in weak and sensitive soil subject to shear strength degradation by traditional aggregate pier methods.
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