The Confinement Effect of Geocell under Triaxial Compression Test

Reinforced soil structures have been developed for more than three decades. They have the merits in the aspects of economy and safety, and they also are considered as an ecological engineering method. Among them, geocells has been widely applied to geotechnical engineering; nevertheless, understanding about the effects of the size, shape, as well as number of the pocket of geocell is still unclear. Furthermore, conducting laboratory test on geocell of large size is difficult. Therefore, selecting appropriate parameters for designing geocell-reinforced structures remains a difficult task.

This study used a geocell made of nylon and filled within it with gravels or sands to conduct triaxial compression tests in two different sizes of triaxial cells, 2.8” and 6.0” in
diameter, respectively. The factors considered were soil type, soil with or without reinforcement, as well as the shape (circle, block and hexagon), size and number of the pocket. The effects of these variables on the stress-strain behavior of geocell-reinforced soils were investigated. Test results showed that the difference in friction angle between reinforced soil and unreinforced soil was not much. For various pocket shapes, hexagon pocket showed the highest friction angle. On the other hand, the apparent cohesion of reinforced soil depends largely on the size, shape, and number of the pocket, of which the most significant factor is the pocket size. In other words, the soil reinforced with geocell of smaller pocket exhibited greater apparent cohesion. Moreover, the smooth circular pocket induced the highest apparent cohesion among all shapes, while that of hexagon pocket is the lowest. Remarkably, for same size and same shape of pocket, the apparent cohesion decreased with increasing number of pocket. In addition, as the confining stress on the reinforced soil increased the reinforcing
effect became less significant, meaning that the effectiveness of reinforcement is more significant when under small overburden pressure. As to the grain size of soil, reinforced-gravel displayed better reinforcing effect than reinforced-sand. This result suggests that geocell is more effective to soil with larger grain sizes.

Theoretical formulae are also used to estimate the increases in deviatoric stress and hoop tensile stress that induced by geocell, respectively, and the comparison is made between
analytical and test results. It was found that the behavior of reinforced soil under low confining stress is similar to the prediction by hoop tension theory. When under high
confining stress the compression shell theory is appropriate to predict the behavior of reinforced soil.