Designing Piled Raft Foundations Using Simplified Analysis Methods

Abstract

There are many factors affecting the load-settlement behavior of the piled raft system. The physical and mechanical properties of the soil, raft foundation and pile foundation have an important effect on this behavior. It is also known that construction stages of buildings also affect this behavior. There are a number of simplified, approximate and advanced methods for analyzing such a complex system. It is possible to reach the most realistic results in analyzes using advanced finite element methods. However, in order to use advanced analysis methods, both high-qualified computers are required and analysis times are very long. For this reason, it will be easier for engineers to solve the problem in a shorter time and with a satisfactory accuracy. In the scope of this study, a piled raft system was analyzed according to different analysis methods such as Terzaghi and Peck (1967), Tomlinson (2001), Wiesner and Brown (1975), Gok and Togrol (2009), Randolph (1994), Poulos-Davis-Randolph, modifying Poulos-Davis-Randolph and simplified finite element (Plaxis 2D) methods considering that a raft foundation of 20m by 20m constructed on a silty clay had a base pressure of 200 kPa. In all methods, the load sharing ratios between the pile group and the raft foundation and the settlement amount of the pile raft system under the structural load were determined. When the pile design is done according to the pile raft analysis, 64 piles are sufficient as D=0.8m, L=19m and s=2.74m. It has been found that the pile group can carry 75-89% of the total load if the foundation system is designed as a pile raft system instead of the conventional method. According to the methods used, the settlement values range from 4cm to 14.5cm.

Keywords

• Analyzing methods
• load sharing ratio
• piled raft system
• settlement
• simplified methods

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