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At relatively lower settlement range the value of does not change much with change in relative density of soil,indicating that the percentage increase in bearing capacity due to the geocell reinforcement is almost the same for all the density of fill soil varying from loose to dense. While, at higher settlement range ,the rate of increase of bearing capacity factor with increase in relative density is substantially high for dense soil (i.e.,ID50%) compared to that for loose soil.This indicates that at relatively higher settlement of footing,the percentage increase in bearing capacity due to the geocell reinforcement (with respect to the unreinforced soil) is higher for dense soil.
Fig. 6. Deformation of foundation surface versus footing settlement
Fig.7.Strain in geocell wall for soil at 70 and 30% relative density
In Fig.6,which depicts the pattern of deformation on fill surface （ ; average of left- and right-hand side dial gauges, and , reading）,heave is shown through sign and settlement through sign.The responses for unreinforced soil bed are shown through dotted line and those for geocell-reinforced soil are shown through solid line.It could be observed that the unreinforced sand bed has undergone heaving more than 5% of footing width, while with geocell reinforcement it is less than 2%.Besides,the soils with higher relative density have undergone
higher surface heaving because of volumetric expansion.In case of unreinforced soil, with dense condition （ID=70 and 60%） heaving starts at a settlement equal to about 9% of footing width and it is at about 15% of footing width for loose soil （ID=40 and 30%）.In case with geocell reinforcement,for all the relative densities of soil, there occurs a zone where there is no change in surface deformation （indicated through a segment of horizontal line in the surface deformation-footing settlement responses）.For dense soil the no-surface-deformation zone starts at a footing settlement equal to about 9% of footing width.It may be the stage
where the geocell by virtue of its confinement suppresses dilation in the soil;thereby, higher strength of geocell material is mobilized.This could be the reason for rapid increase in values beyond settlement of about 0.1B as compared to that at lower settlements （Fig. 5）.Since soil needs certain amount of deformation to dilate,at lower settlement range substantial part of foundation soil remains dormant;therefore percentage increase in bearing capacity due to the geocell reinforcement is almost the same both for loose and dense soils （Fig. 5）.This is reflected in the observation （Fig. 6） that at lower settlement of footing ,for all the relative density of soil, the geocell mattress has not shown any heaving.For loose soil （ID=30 and 40%） the geocell mattress heaves marginally only at very large settlement of footing. In this case the no-surface-deformation zone starts at a footing settlement equal to about 25% of footing width. Fig.5 shows that for s /B 25%,even for loose soil （ID=30 and 40%） the improvement factor shows a visibly increasing trend with increase in relative density. This is attributed to the reason that the vertical movement of footing is accompanied by compression of soil underneath. With very large settlement of footing, the soil below gets dense and hence the behavior is similar to that of the dense soil.
Besides, the surface settlements are generally found to be lower for higher density of soil,which may be due to the increase in subgrade strength and end anchorage from soil that resists the downward deflection of the geocell mattress,giving rise to higher performance improvement. In the tests with loose soil fill,the two free ends of the geocell mattress were visible at the soil surface at large footing settlements. This result clearly shows that there was not enough anchorage at the two ends of the geocell mattress in the case of loose soil.