Abstract—When the foundations of structures under cyclic loading with amplitudes less than their permissible load, the concern exists often for the amount of uniform and non-uniform settlement of such structures. Storage tank foundations with numerous filling and discharging and railways ballast course under repeating transportation loads are examples of such conditions. This paper deals with the effects of using the new generation of reinforcements, Grid-Anchor, for the purpose of reducing the permanent settlement of these foundations under the influence of different proportions of the ultimate load. Other items such as the type and the number of reinforcements as well as the number of loading cycles are studied numerically. Numerical models were made using the Plaxis3D Tunnel finite element code. The results show that by using grid- anchor and increasing the number of their layers in the same proportion as that of the cyclic load being applied, the amount of permanent settlement decreases up to 42% relative to unreinforced condition depends on the number of reinforcement layers and percent of applied load and the number of loading cycles to reach a constant value of dimensionless settlement decreases up to 20% relative to unreinforced condition. Keywords—Shallow foundation, Reinforced soil, Cyclic loading, Grid-Anchor, Numerical analysis. I. INTRODUCTION EHAVIOR of foundations on reinforced sand beds is one of the most interesting topics in geotechnical engineering. The type and the quality of reinforcements have been changed a lot. The use of polymeric reinforcements such as geotextiles, geogrids and geonets has been increasingly expanding. Up to now, many experimental and numerical studies have been made to determine the bearing capacity of shallow foundations on different soils reinforced by different elements such as metal strips, metal rods, tire shreds and geosynthetics [1]-[4]. Fig. 1 shows the classical scheme of a system of reinforced soil for a square foundation with B×B dimensions and N reinforcement layers. The dimensions of reinforcements Ph.D. Candidate in Geomechanics, Department of Civil Engineering, Shiraz University , Shiraz, I.R. Iran (Corresponding author to provide phone: +98 (917) 702 8072; fax: +98 (711) 6473161; e-mail: ahajiani@gmail.com). Professor, Department of Civil Engineering, Shiraz University, Shiraz, I.R. Iran (e-mail: nhataf@shirazu.ac.ir). Professor, Department of Civil Engineering, Shiraz University, Shiraz, I.R. Iran (e-mail: ghahrama@shirazu.ac.ir). are b×b and the distance between their first layer and the foundation bottom is denoted by u. the depth of the reinforcement area can be found using equation 1. ( 1) d u N h = + − (1) Fig. 1 Shallow square foundation supported by geogrid-reinforced sand Previous studies have given different optimal values for the ratios u/B, b/B and h/B for optimizing the bearing capacity of shallow foundations [1]-[5]. Binquet and Lee (1975) and Guido et al. (1986) showed that the ratio u/B for the most suitable state possible of the influence of the use of the reinforcement must be chosen as less than 0.67 [1], [4]. They provided also the values of (b/B) cr and (d/B) cr for a square foundation on the sandy soil reinforced by the geogrid to be 2 to 3 and 1.25 respectively. Yetimuglu et al. (1994) found that the critical value of u/B, h/B and b/B were equal to 0.25, 0.2 and 4.5 respectively [6]. Adams and Collin (1997) also conducted a comprehensive study on geogrid and geocell reinforced foundations on 34 large-scale models [7]. Bearing capacity ratio (BCR=q r /q ur ) which is defined as the ratio of the bearing capacity of the reinforced soil (q r ) to that of the unreinforced soil (q ur ), was reported to be 2.63 for the geogrid reinforced foundations while BCR = 1.27 for the geocell-reinforced foundations. Das et al. (1994) investigated the behavior of strip footing on geogrid reinforced sand [8]. They found that full depth geogrid reinforcement may reduce the permanent settlement of a foundation by about 20% to 30% compared to one without reinforcement. Unikrishnan et al. (2002) conducted laboratory triaxial tests to investigate the behavior of reinforced clay under monotonic and cyclic loading. They found that due to provision of sand layers on either side of the reinforcement (sandwich technique) within reinforced clay soils, the response of reinforced clay soil by way of enhanced interfacial bond was improved [9]. Boushehrian and Hataf Numerical Study of Cyclic Behavior of Shallow Foundations on Sand Reinforced with Geogrid and Grid-Anchor Alireza Hajiani Boushehrian, Nader Hataf and Arsalan Ghahramani B World Academy of Science, Engineering and Technology 58 2009 607