Large scale field tests on geogrid-reinforced granular fill underlain by clay soil Ahmet Demir a , Mustafa Laman b, * , Abdulazim Yildiz b , Murat Ornek c a Osmaniye Korkut Ata University, Civil Engineering Department, 80000 Osmaniye, Turkey b Cukurova University, Civil Engineering Department, 01330 Balcali, Adana, Turkey c Mustafa Kemal University, Civil Engineering Department, 31200 Iskenderun, Hatay, Turkey article info Article history: Received 1 June 2011 Received in revised form 11 April 2012 Accepted 22 May 2012 Available online xxx Keywords: Field test Geogrid Natural clay Granular fill Subgrade modulus Bearing capacity abstract This study aims at experimentally explaining the potential benefits of geogrid reinforced soil footings using large scale field tests. A total of 16 field tests were carried out to evaluate the effects of replacing natural clay soil with stiffer granular fill layer and single-multiple layers of geogrid reinforcement placed into granular fill below circular footings. The large scale field tests were performed using different size of the circular footing diameters which have 0.30, 0.45, 0.60 and 0.90 m. The results of testing program are presented in terms of subgrade modulus and bearing capacity. These values were calculated for each test at settlements of 10, 20 and 30 mm. Based on the test results, it is shown that the use of granular fill and geogrid for reinforced soil footings (RSF) have considerable effects on the subgrade modulus and bearing capacity. Finally, the field test results are compared to the analytical methods proposed by different researchers including the statistical correlations. Ó 2012 Published by Elsevier Ltd. 1. Introduction In many cases of construction, shallow foundations are built on top of existing cohesive soils, resulting in low bearing capacity and/ or excessive settlement problems. An economical treatment method is the use of reinforced soil foundation (RSF). This can be done by either reinforcing cohesive soil directly or replacing the poor soils with stronger granular fill, in combination with geo- synthetics. In this technique, one or more layers of a geosynthetic reinforcement and controlled fill material are placed beneath the footing to create a composite material with improved performance characteristics. This technique is commonly used for unpaved roads, embankments, and large stabilized areas such as car parks or working platforms for oil drilling (Giroud and Noiray, 1981; Giroud et al., 1984; Rowe and Soderman, 1986; Love et al., 1987; Fannin and Sigurdsson, 1996; Miura et al., 1990; Ling and Liu, 2001; Rowe and Li, 2005; Hufenus et al., 2006). In comparison with other applica- tions of geosynthetic-reinforced soil, relatively less emphasis has been placed on reinforced soil foundations. There have been some studies of shallow foundations on reinforced soil systems, most of them concentrating on sandy soil (Adams and Collin, 1997; Gabr and Hart, 2000; Fonseca, 2001; DeMerchant et al., 2002; Fukushima et al., 2003; Latha and Somwanshi, 2009). Analytical models have been proposed for calculation of the bearing capacity of a compacted sand or gravel layer on soft clay (Chen and Davidson, 1973; Hanna and Meyerhof, 1980; Love et al., 1987; Florkiewicz, 1989; Michalowski and Shi, 1995; Lyons and Fannin, 2006; Sharma et al., 2009). However, a limited number of experimental studies are avail- able at the present time relating to the bearing capacity of shallow foundations on reinforced granular material of limited thickness overlying soft clay (Love et al., 1987; King et al., 1993; Ornek, 2009; Consoli et al., 2009; Mohamed, 2010). Love et al. (1987) studied the effectiveness of geogrid reinforcement, placed at the base of a layer of granular fill on the surface of clay by small-scale model tests in the laboratory. In the tests, only one geogrid layer was used at the interface between granular fill and clay soil. They showed that performance of reinforcement systems to be excellent even at small deformations, due to the significant change in the pattern of shear forces acting on the surface of the clay. King et al. (1993) carried out some laboratory model tests to evaluate the improvement of ulti- mate bearing capacity of shallow strip foundation supported by a strong sand layer underlain by weak clay with a layer of geogrid at * Corresponding author. Tel./fax: þ90 322 338 6702. E-mail addresses: ahmetdemir@osmaniye.edu.tr (A. Demir), mlaman@ adanabtu.edu.tr (M. Laman), azim@cukurova.edu.tr (A. Yildiz), mornek@ mku.edu.tr (M. Ornek). Contents lists available at SciVerse ScienceDirect Geotextiles and Geomembranes journal homepage: www.elsevier.com/locate/geotexmem 0266-1144/$ e see front matter Ó 2012 Published by Elsevier Ltd. doi:10.1016/j.geotexmem.2012.05.007 Geotextiles and Geomembranes xxx (2012) 1e15 Please cite this article in press as: Demir, A., et al., Large scale field tests on geogrid-reinforced granular fill underlain by clay soil, Geotextiles and Geomembranes (2012), doi:10.1016/j.geotexmem.2012.05.007