Dominant elastoplastic behavior of geocell-reinforced sand subjected to cyclic loading under large-scale triaxial tests

The beneficial effects of geocells on improving the soils' characteristics have always drawn researchers' atten-tion. However, due to the geocell's large scale, more accurate analyses, such as large-scale cyclic laboratory tests, are still needed to determine the soil-geocell system's actual mechanism. In the present research, a series of large-scale triaxial tests are carried out on poorly graded sand samples with 30 cm diameter and 60 cm height rein-forced by geocell with heights of 0.6, 1.0, and 1.4 of the pocket diameter and placement depths of 0.05, 0.15, 0.25, and 0.35 of the samples' height under static and cyclic loading conditions. Contrary to common opinion, the results obtained for unreinforced sands showed that the maximum bulge, instead of the middle, occurred at 0.25 of the sample's height from the top surface. Changing the bulging from the middle to the upper part reflects the role of the direction of stress applied and the accumulation of the deformation due to plastic behavior near the load position. On the one hand, the results of static tests revealed that placing geocell at this depth delivers the best performance in controlling the bulging and reducing settlement values due to the predominant lateral support to the sand particles, reducing the localized stress concentrations, increasing internal friction and interlocking, and reducing the likelihood of shear failure. On the other hand, the geocell with moderate height had higher wall rigidity and stability against deformations compared to the geocell with lower and higher height values due to higher soil confinement potential and more resistance against buckling, respectively. Cyclic loading was also performed on geocell-reinforced soils under 110 cycles with cumulative strains ranging from 0.13 to 0.155 %. The cumulative strains for the unreinforced and reinforced soils were 0.196 % and in the range of 0.130-0.154 %, respectively. The best geocell placement depth under cyclic loading mode was at 0.05 of the sample's height, which had a cumulative strain of 0.13 % in 110 cycles and reduced the cumulative strain by about 34 % compared to the unreinforced sample. The presence of geocell in the soil generally led to an increase in the shear modulus and a decrease in the slope of the damping ratio. Further, the shear modulus was reduced by increasing the geocell placement depth.