An Analytical Approach for Piled-Raft Foundation Design Based on Equivalent Pier and Raft Analyses by Using 2D Finite Element Method

Abstract

The piled-raft foundation systems have started to be a very popular design method that is commonly used for especially high-rise buildings. In this foundation system, both raft and piles share the applied loads coming from the supper structures. There are several methods proposed by researchers in order to solve piled-raft foundation problems by simplified methods, approximate methods, and more sophisticated computer-based methods. These sophisticated computer-based solutions are not simply adapted to geotechnical works, and accessing these programs by everyone is not easy. The main purpose of this study is to present an easy and new technique for solving piled-raft problems with using 2D-FEM analysis combined with equivalent pier. In this study, design concepts of a pile-raft system prepared by 2D-FEM analysis combined with equivalent pier were presented. Furthermore, the test results obtained from this method were compared with the results that were taken from equivalent raft method and equivalent pier with single pile response in a sandy soil. A generic example of a piled-raft system including 3 × 3 number piles was designed, and its some properties such as length of pile (10–28 m), pier-soil stiffness ratio (1000–5000), and spacing between the piles (2–4 m) were evaluated and compared as variables. It was concluded from this study that equivalent pier with 2D-FEM analysis can make very similar predictions for calculating settlements of piled-raft system regarding on equivalent pier with single pile response method. As a result of this study: (1) as aspect ratio of piled-raft system increases, raft to pile stiffness ratio gradually increases for all s/d ratios, (2) the efficiency exponents obtained from this study ranges between 0.46 and 0.58 values, (3) stiffness of the piled-raft system gradually increases with increase of slenderness ratio for both two equivalent pier methods, and (4) as slenderness ratio increases, stiffness ratio of the piled-raft system contrarily decreases.