Stone columns are being used for the stabilization of a natural slope for the construction of a bridge embankment. The stone column has 2 primary functions 1) increase shear strength along the slip surface and 2) provide pressure relief due to the location of an artesian aquifer below the construction site. The columns are being installed through a heavily over-consolidated predominantly silt or silt clay (CL-ML) with a potential shear zone of SILT and CLAY (CI-CH). The base of the stone column will be completed in a highly over-consolidated low permeability sandy silt till separating the artesian aquifer from the base of the column by 5-7 m. The stone gradation is very coarse and was selected primarily for its shear strength characteristics. My concern is with piping of fines into the voids of the stone column. Fines are >85% in the base soil, and there will be a high pressure gradient near the base of the column due to the artesian aquifer. My thinking is that actual seepage velocities should be low given the low permeability of the in situ soil, so I don't know if piping will be an issue. If piping is an issue could I be concerned with a piping failure? Would a geosynthetic provide adequate filtration if installed in the column prior to the stone? I would like to maintain the stone gradation for strength. Any good references on geotextile selection (proper AOS, permeability, filtration, etc.). Thanks in advance for any suggestions.
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