3D numerical analysis of piled raft foundation in stone column improved soft soil

Abstract

Abstract The concept of composite piled raft foundation incorporates piles of different lengths and stiffness, where short columns of flexible materials improve the shallow soft soil and longer columns of relatively rigid material support loads and reduce settlement. Present study utilised this concept by employing stone columns beneath the piled raft foundation and investigated its response through three-dimensional finite element analyses. Effects of area replacement ratio, slenderness ratio and material properties of stone column, slenderness ratio of pile and thickness of raft have been examined on the proportion of load shared by piles and stone columns and settlement response of piled raft under different levels of vertical load. Results showed that strengthening the shallow soft soil with stone columns was effective in improving the bearing interaction of raft, i.e. increasing the proportion of load shared by stone columns, and reducing the total settlement of the piled raft. Percentage load shared by piles was significantly influenced by the slenderness ratio of piles and level of vertical load on raft, but was almost independent of properties of stone columns and thickness of raft. Increment in diameter of stone columns (area replacement ratio) significantly improved the bearing interaction of raft, and increment in their lengths (slenderness ratio of stone columns) reduced the settlements of the foundation system. Increase in angle of friction of constituent stone column material improved both the bearing interaction of raft and settlement performance of the foundation system. Increment in raft thickness not only enhanced the proportion of load shared by stone columns, but also drastically reduced the total and differential settlements of the foundation.