International Journal of Civil Engineering, Vol. 13, No. 2, Transaction B: Geotechnical Engineering, June 2015 Centrifuge modeling of non-connected piled raft system H. Rasouli 1 , A. Saeedi Azizkandi 2, *, M.H. Baziar 3 , M. Modarresi 4 , H. Shahnazari 5 Received: February 2015, Revised: May 2015, Accepted: June 2015 Abstract In present research, 17 centrifuge tests have been conducted to study the effect of various parameters such as the number of piles, the distance between piles, gradation and thickness of the granular layer on the load-settlement behavior of a pile raft system. The results showed the importance of granular layer to reduce the settlement of non-connected pile raft system when the roles of piles are to reduce the settlement. In other words when the piles have major contribution on the bearing capacity of pile raft system, presence of a granular layer may increase the settlement. Keywords: Piled raft foundation, Non-connected piled raft, Load-settlement behavior and settlement reduction. 1. Introduction The pile raft foundation systems have been previously designed assuming the structural loads to be completely carried by the piles even if the piles were added only to reduce settlements. In the recent decades, a new method called pile raft system or pile raft settlement reducer system has been introduced which the bearing capacity mechanism of its system is somehow between shallow and deep foundation systems. The concept of a pile-raft system was first introduced by Davis and Poulos in 1972 [1]. The application of piles as only settlement reducers was first suggested by Burland et al. [2], Up to now, various studies have been reported on the application of settlement-reducer piles (Hansbo [3], Burland [2], Hirokoshi and Randolph [4], Viggiani [5], Poulos [6], Russo and Viggiani [7], Mandolini [8], Randolph et al. [9]). The basic concept of this approach is to consider the foundation as a number of piles responsible for reducing the settlement to an acceptable level. These piles also carry a portion of the structural loads transferred from the foundation raft to piles. In other words, some portion of the load is taken by the foundation and the rest is tolerated by the piles. When the piles are used as settlement reducer, * Corresponding author: asaeedia@iust.ac.ir 1 MSc. Student, School of Civil Engineering, Iran University of Science and Technology, Tehran, Iran 2 Assistant Professor, School of Civil Engineering, Iran University of Science and Technology, Tehran, Iran 3 Professor, School of Civil Engineering, Iran University of Science and Technology, Tehran, Iran 4 MSc. Student, School of Civil Engineering, Iran University of Science and Technology, Tehran, Iran 5 Associate Professor, School of Civil Engineering, Iran University of Science and Technology, Tehran, Iran their entire bearing capacity may be mobilized because, a very little settlement in soil is needed to mobilize the full bearing capacity of shaft pile. Clency and Randolph [10] suggested that in order to effectively design the foundations with settlement reducer piles, the bearing capacity of piles should be considered equal to 80% of the service load. Generally the low number of piles in a pile raft system can cause very big bending moments as well as cracks and axial stress concentration at the tip of the piles. In the seismically active areas, in the piles sections connected to the raft, very big shear forces as well as failure moments can develop at their tip due to the lateral dynamic load. Haghbin [11] examines the behavior of soil-reinforced piles and applied loads based on the analytical method and by using the numerical results of FLAC3D software for comparison with the analytical results. The analysis was based on a method called virtual retaining wall, with the following considerations: an imaginary retaining wall that passes the footing edge; the bearing capacity of footing on reinforced soil with piles, which was determined by applying equilibrium between active and passive forces on virtual wall; and a pile row that exists beneath the shallow foundation. To calculate the lateral pile resistance here, an analytical equation was then required. Results showed that the analytical method, while being close to other methods, was more conservative. In these cases, the possibility of foundation structural failure is greater than the soil failure. Thus, in order to increase the bending moment of piles and prevent the structural damage, the dimensions of piles have to be increased. In most design codes (ASTM 1969, British Standard 1986, Singapore Code 2002) strong limitations have been imposed for the allowable stresses in the piles which may lead to uneconomical design of the foundation system. Therefore, Wang et al. [12] suggested that in order to overcome the large stresses between the foundation and Geotechnique