Performance of circular footings on sand by use of multiple-geocell or -planar geotextile reinforcing layers

This paper describes a series of reduced scale tests, at unit gravity, performed on circular footings supported by reinforced sand. Reinforcement by multiple layers of geocell was investigated and the performance of the footing was compared to one on the same sandy soil containing multi-layered planar geotextile reinforcement. The comparison used geocell and geotextile layers formed from the same parent geosynthetic material having the same characteristics but with a lower geocell mass. Results show that the efficiency of the reinforcement (described in terms of the load carrying and subgrade modulus enhancement) decreased as the number of layers increased. In tests at moderate and low footing settlements, significant improvements in bearing capacity and subgrade modulus were obtained with the application of three layers of geocell. On the whole, multi-layered geocell-reinforced soil provides a more effective and much stiffer system capable of delivering greater foundation loads and subgrade modulus than multi-layered planar-reinforced soil, even when less parent geosynthetic material is used in the multi-layered geocell arrangement. Furthermore, reinforcement benefit is achievable at settlements as small as 0.2-0.4% of the footing diameter for the geocell installations, whereas settlements 4 to 5 times larger are needed before benefit is gained from a comparable planar geotextile system. To achieve comparable performances, the multi-layered geocell requires 1/4 to 1/2 the mass of geosynthetic material as that needed for multi-layered planar geotextile reinforcement (depending on the settlement allowable). The multi-layered geocell reinforcement requires considerably less parent geosynthetic material (reducing transport and, perhaps supply costs), and because the size of reinforcement zone required is considerably smaller, the amount of excavation and backfill required is also significantly reduced.