A Numerical Study on the Behavior of Stone Columns With Different Area Ratios in Soft Clays

Abstract

The single floating stone column behavior in very soft soils with a low undrained shear strength of Cu ≤ 20 kN/m2 was studied in the finite-element method to investigate the influence of stone column's area ratio on the normalized pressure-settlement curves of circular footings of different diameters. The studied cases consist of stone columns of 1.0 m in diameter Ds and lengths Ls of (4 m, 6 m, and 7.5 m). The diameter of footings Df is (1.0 m, 1.2 m, 1.4 m, 1.6 m, 2.0 m, 2.5 m, and 3.5 m) which covers the area ratios with a range of 100 to 8.16 %. A total of 28 runs were carried out using the Ansys program to simulate the case for improved and unimproved soil. In the axisymmetric numerical model, the connection between the stone column and the adjacent contact clay soil was modeled as bonded type. The results of the analysis showed that there is a clear relationship between the bearing ratio (q/cu improved) / (q/cu unimproved) and the normalized settlement (S/Df) of the composite structure and the area ratio Ar% of the stone columns. The deformation ratio (Streated/Suntreated) and the footing diameter are related using a straightforward equation. In comparison to footings with a low area ratio, the footing displays a lower value of settling when subjected to the same pressure. By decreasing the diameter of the footing, the normalized settlement decreases for the same normalized q/cu values. The bearing ratio depends on the stone column length ratio Ls/Ds and settlement ratio. It is from 2.2 at a 100% area ratio and 1.23 at a 16% area ratio.