The effect of sand columns on the response of clay under cycled loading conditions

Abstract

The reliance on granular columnar inclusions for improving the bearing capacity of soft clays, reducing overall settlements, and accelerating consolidation due to applied static loads is an established ground modification solution. The improvement achieved by reinforcing soft clays with aggregate piers has been extensively studied and quantified both in experimental and real world application contexts. To date however, few attempts have addressed the resultant effect-improvement on the site response under dynamic loading conditions. This research effort investigates the effect of columnar granular inclusions on the cyclic resistance of isotropically and 1-dimensionally consolidated clay samples. A series of stress-controlled cyclic tests were conducted on both “control” and sand-column reinforced samples across a range of parameterized conditions. The effect of varying the cyclic stress amplitude and frequency as representatives of induced shear stresses and rate effects respectively was investigated under both drained and undrained conditions. Furthermore, the effects of a range of practical design values of area-replacement ratios and column densities were investigated. Image processing and tomographic techniques were utilized to assist in tracking sample deformation, particularly in the radial and axial directions. The pore water pressures generated during the various phases of loading were independently monitored for the clay matrix and at the granular column location. The effectiveness of granular columns under these parameters for design purposes were assessed and compared with current design practice.