Proceedings of Indian Geotechnical Conference December 13-15,2012, Delhi (Paper No. E 512.) PERFORMANCE OF SHALLOW FOOTING ON GEOCELL REINFORCED CLAY BED USING EXPERIMENTAL AND NUMERICAL STUDIES A. Hegde, Research Scholar, Deptt. of Civil Engg, Indian Institute of Science, Bangalore, amarnath@civil.iisc.ernet.in T.G. Sitharam, Professor, Deptt. of Civil Engg., Indian Institute of Science, Bangalore, sitharam@civil.iisc.ernet.in ABSTRACT: This paper summarizes the beneficial effect of geocell reinforcement in soft clay beds through 1-g model plate load tests and numerical simulations using FLAC 2D . New commercially available PRS Neoweb geocells are used in the investigation; which is known for its high strength and durability. Results show that provision of geocell increases the load carrying capacity of soft clay bed by 5 times. The overall performance of the clay bed improves further due to the provision of planar geogrid at the base of the geocell. Numerical results are also in the same line with the experimental findings. INTRODUCTION Construction in soft ground has always been a big challenge for the engineers. Construction in weak ground requires treating large areas to a greater depth to ensure the safety of the superstructure. Whenever the soft soil is encountered, the general tendency is to go for the deep foundation technique like plié foundations or the ground improvement technique like vibro stone columns. But in the situations involving the low to moderate loading condition, deep foundations become very costly and in such cases more economical solutions are constantly sought after. Reinforcing the soil with the geocell is emerging as the one of the most the cost effective as well as alternative solution to the deep foundation techniques in some cases. It is well known fact from the past research is that the geocell reinforcement increases the load carrying capacity of the foundation bed. Since late 1970’s, many researchers have studied the beneficial effect of the cellular reinforcement through laboratory model plate load tests such as Brooms and Massarach (1977) and Mitchell et al. (1979) . But the majority of the past studies carried out were using laboratory prepared 3D cells made up of paper, geogrids, PVC (Polyvinyl Chloride), geotextiles etc. (Dash et al. 2001; Sitharam and Sireesh, 2004; EI Sawwaf and Nazer, 2005; Madhavi Latha and Somwanshi, 2009; Tafreshi and Dawson , 2010). Very few researchers directly used the commercially available geocell in their studies (Guido et al. 1989; Kief and Rajgopal, 2008). Use of the commercial geocell in the laboratory study is more relevant because, those are the ones, which will be directly utilized in soft soil. In the present study, new commercially available Neoweb geocells (PRS- 330) are used; which is known for its high strength and durability. The primary objective of this study is to evaluate the improvement in the overall performance of the footing in the presence of commercially available Neoweb geocell. Results of the laboratory model tests and the numerical simulations on a square footing resting on reinforced clay beds are reported in this paper. LABORATORY MODEL TESTS Laboratory model plate load tests were conducted on test bed cum loading frame assembly. Foundation bed was prepared in a test tank having dimension of 900mm length, 900mm width and 600mm height. The footing used in the study was square in shape with 150mm sides, made up of rigid steel plate with 20mm thickness. The base of the footing was made rough by coating a thin layer of sand to it using epoxy glue. Footing was loaded with hand operated hydraulic jack supported against self-reacting frame. The load applied to the footing was measured through a pre-calibrated proving ring, which was placed between hydraulic jack and the footing with the ball bearing arrangement. Schematic representation of test setup is shown in Fig.1. Fig. 1 Schematic representation of test set-up Natural silty clay was used to prepare the foundation bed. The liquid limit, plastic limit and specific gravity of the soil were 40%, 19% and 2.66. As per Indian Standard Soil Classification System (ISSCS), soil can be classified as clay with medium compressibility (CI). The geocell used in the study was made up of polyethylene with a density of 0.95 g/cm 3 . The each cell is 250mm long, 210mm wide and 150mm deep. The thickness of the strip is 1.53mm with cell to cell seam strength is 2150N. Biaxial geogrid made up Polypropylene with aperture size 35mm x 35mm was used.