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The pattern of strain variation in geocell wall for dense soil （ID=70%） and loose soil （ID=30%） is shown in Fig. 7.It could be observed that,in case of dense soil compressive strains are induced at （or near） two free ends of the geocell mattress.Due to dilation of soil in the regions of loading,there develops a volume expansion of sand,through aperture opening of geogrid walls.This expansion of soil is mostly in the transverse direction; as in the vertical direction there is infinite zone of soil.This localized transverse expansion is restrained by the sand in the adjacent stable region.Such a restraint produces compression in the soil mass thereby giving rise to compression in the geocell wall. Fig. 7 b shows that in the case of loose sand, compressive strains
have not developed anywhere in the mattress.This is because of the absence of dilation induced volume expansions in the loose soil.This observation once again reinforces the earlier conclusions regarding the infill soil dilation induced behavior of geocell mattress.
Fig. 8. Deformation pattern of soil below geocell mattress （ID
=70%）
The observed deformation pattern of subgrade soil below geocell
mattress （Fig. 8）,under footing loading,indicates that the geocell mattress behaves as a wide slab that transmits the footing pressure to the underlying soil layer and redistributes over a wider width . is the increase in footing width at the base of geocell mattress （i.e., at depth of ） due to the wide slab effect load spreading angle within the geocell mattress . was measured from the observed rupture surface in the sand subgrade delineated through the discontinuity in the white colored sand layers （Fig. 8）.Using the above formulation and the measured values of the load spreading angle in the geocell mattress is calculated as
（1）
Fig. 9 that depicts the relationship between the calculated values of and relative density shows that the load spreading angle in geocell mattress increases with increase in density of the foundation soil.It also shows that for ID 40%, increases rapidly with increase in relative density of soil.This indicates that the influence of the geocell reinforcement in improving the rigidity of the quasirigid geocell mattress slab,underneath the footing,is more efficient for dense condition of the foundation soil.
Fig. 9. Load dispersion angle in geocell foundation versus relative
density of soil
The present observations in case with geocell reinforcement are in contrary to the findings of Fragaszy and Lawton （1984） in case of planar reinforcement. With planar reinforcement at 4% settlement the values of the bearing capacity ratio same as ） for ID=51,61,70,80,and 90% are 1.2,1.2,1.4,1.5,and 1.5, respectively.Whereas, at settlement close to failure （i.e., s=10% of B） it is 1.6,1.7,1.7,1.7,and 1.6, respectively （Fragaszy and Lawton 1984）.These results indicate that at relatively lower settlement range the performance improvement,due to planar reinforcement,increases with increase in relative density of
soil, whereas at higher settlement range close to failure,the performance
improvement is independent of soil density.In case of planar reinforcement system, the reinforcing effect is mostly due to interfacial frictional resistance mobilized through deformation （Sitharam et al. 2005）.Therefore,at settlement close to failure the soil shears away with large proportion of reinforcement strength remaining immobilized.Whereas the geocell system being an allround confining system restrains soil flow, thereby the encapsulated soil does not shear away.Hence,with increased density,the dilation induced benefit is more at higher settlement of footing.