Influence of Relative Density of Soil on Performance of Geocell-Reinforced Sand Foundations Sujit Kumar Dash1Abstract: The paper brings out the influence of relative density of foundation soil on performance improvement of geocell reinforcement;52534

through model load tests on geocell-reinforced and unreinforced sand beds.Tests were carried out for five different relative densities of sand (30, 40, 50, 60, and 70%）.The test results indicate that the beneficial effect of geocell reinforcement,in terms of increase in stiffness, bearing capacity,and load dispersion angle of the foundation bed,is present over a wide range of relative density; however,it is higher for dense condition of foundation soil.With geocell reinforcement offering three-dimensional confinement,the dilation induced benefit is substantially high for dense soil fill.Therefore,for effective utilization of geocell reinforcement, the foundation soil should be compacted to higher density.

DOI: 10.1061/(ASCE)MT.1943-5533.0000040

CE Database subject headings: Foundations;Soil stabilization; Reinforcement;Model studies;Relative density;Sand,soil type.

Author keywords: Foundation bed;Reinforced soil;Geocell reinforcement;Relative density;Model studies.

Introduction

     The geocell mattress consists of a series of interlocking cells constructed from polymer grid reinforcement,which contains and confines the soil within its pockets.This composite mattress,in the present day, is being used in improving the performance of foundation soil in many cases such as beneath the pavements and railroads,at the base of earth embankments,foundations for liquid storage tanks and oil exploration platforms, etc.(Mitchell et al. 1979; Bathurst and Jarrett 1989; Bush et al. 1990; Dash et al. 2001, 2003a,b, 2008; Zhou and Wen 2008; Sireesh et al. 2009).This paper presents the results from a series of laboratory model tests designed to bring out the influence of relative density (ID) of the foundation soil on the performance of geocell-reinforced sand

foundation beds.

Experimental Program

    The model tests were conducted in a steel framed tank having length of 1,200 mm, width of 332 mm, and height of 700 mm.The model footing, made of steel, had length of 330 mm， width of 100 mm, and thickness of 25 mm.The footing was centered in the tank,with the length of the footing parallel to the width of the tank.

     The soil used is a poorly graded sand with effective particle size ( )of 0.22 mm and average particle size ( ) of 0.46 mm.The minimum void ratio ( ) as determined using a vibratory table (ASTM 2006b) is 0.474.The maximum void ratio ( ) is 0.795 (ASTM 2006a).The peak friction angles of the sand were obtained as 39.2°, 41°, and 42.2° from triaxial compression tests at relative densities  , where   situ void ratio  of 30, 50 and 70%,respectively.The dilation angles of the sand,obtained from direct shear tests （Gibson 1953） at these relative densities,are found to be 0°, 6°, and 20°, respectively.

    The geocell reinforcement was fabricated using a biaxial geogrid

made of oriented polymer,having aperture opening size of 35 35 mm, ultimate tensile strength of 20 kN/m, and 5% strain secant modulus of 160 kN/m （ASTM 2001）.As shown in Fig. 1（b）,the geocell mattresses were prepared by cutting the geogrids to required length and height from full rolls and placing them in transverse and diagonal directions with bodkin joints （Simac 1990; Carroll and Curtis 1990） at the connections （Bush et al. 1990）.The bodkins in the present tests are 6-mm-wide and 3-mmthick

plastic strips made of low-density polypropylene.The joint strength of geocell, obtained through tensile test,is 4.75 kN/m. Fig.1 shows the geometry of the problem considered in the present investigation. Three-dimensional sketch and photograph of typical geocell system can be found in Dash et al.（2003a,b）.