Shear Stress Redistribution as a Mechanism to Mitigate the Risk of Liquefaction

The installation of stone columns or piers in a loose, saturated sand deposit can potentially mitigate the risk of liquefaction by decreasing the seismic demand on the soil by redistributing the induced shear stresses from the sand to the columns or piers. In calculating the shear stress redistribution, it is commonly assumed that both the soil and the columns or piers respond as shear beams. Although less common, it has also been assumed that the soil responds as a shear beam and that the columns or piers respond as flexural beams, with the redistribution of the shear stresses computed accordingly. However, the results presented herein show that the columns or piers, and the soil immediately surrounding the column/pier, deform in a combination of shear and flexure. The percent contribution of shear versus flexural deformation of the column or pier varies with depth, with the column/pier deforming predominantly in flexure near the ground surface and predominantly in shear at depth. The percent contribution of each mode of deformation governs the redistribution of the shear stresses from the soil to the pier. The distribution of the shear stresses between the soil and columns or piers are quantified for "typical" properties of a loose, saturated sand profile reinforced with Impact^TM Rammed Aggregate Piers^TM.