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This factor is defined asthe ratio of the footing pressure with the slope reinforced (qrein-forced) to the footing pressure in tests without reinforcement (q). Inthis study pressures that bring a settlement equal to 0.05B wasselected as representative q. The footing settlement (Uy) is alsoexpressed inmm. The bearing capacities for both themodel and theprototype footing are determined from the load-settlement curvesat the 5% of the footing width, after which the footing was assumedto collapse. Typical variations of bearing pressure (q) with settle-ment (Uy) for model and prototype footing are shown in Fig. 8. Thefigure clearly shows that placement of geogrids specially grid-anchorsmuch improves both the initial stiffness (initial slope of theload-settlement curves) and the bearing load at the same settle-ment level.Fig. 9 indicates the results of four tests, ga315, ga15, gg3751 andgg175 (a guide for test names has been presented in Table 3). In alldiagrams in Fig. 9 both experimental and numerical results havebeen shown. As it can be seen in these diagrams, although thenumerical results do not fit completely to the experimental results,but the agreement is reasonably well. This discrepancy may berelated to the model, soil and foundation parameters chosen andthe differences of the boundary conditions in numerical andexperimental models.4.1. Effect of the depth to the top geogrid layerFig. 10 shows variation of BCR and load-settlement behaviorwith u/B. As seen, it is clear that the inclusion of geogrid reinforcements would increase the magnitude of the footingbearing capacity and decreases the settlement of the system.There is a critical embedment depth to footing width ratio u/B ofabout 0.75. On the two sides of the critical u/B ratio, the efficiencyof the reinforcement seems to decrease significantly (as indicatedby the reduction of BCR values). When u/B ¼ 1.0, the performanceof the reinforced slope becomes rather minimal, as showed byBCR approaching unity. These results are highly consistent withthe model test results obtained by Selvadurai and Gnanendran(1989) on Tensar-geogrid reinforced fill slopes constructed ofmortar sand (4 ¼ 43 )(Yoo, 2001; Lee and Manjunath, 2000).These results clearly show that the benefit of a reinforced slopegains its peak when the reinforcement embedment depth is about0.75B. According to Lee and Manjunath (2000), the behaviordescribed in the previous paragraph can be explained by the‘‘deep footing effect’’ as suggested by Huang et al. (1994).Whenthe restraining force exerted by reinforcement is imposed on soilelements, the reorientation of the strain characteristics associatedFig. 8. Effect of reinforcement inclusion on slope response. with the restraint of the minor principal strain of the soil elementsoccurs in the vicinity of the reinforcement (McGown et al., 1978;Tatsuoka and Yamauchi, 1986). A part of the reinforced zonewhere relatively large reinforcement force has developed, behaveslike a part of the rigid footing and transfers a major part of thefooting load into a deeper zone. This load-transfer mechanismseems to reach the optimumwhen the reinforcement embedmentdepth to footing width ratio u/B is about 0.75. At larger depths ofembedment, the contribution to the load transfer mechanismcaused by the presence of the reinforcement reduces significantly.For embedment depth to footing width ratios u/B 1, it wouldappear that the plane of the georeinforcement acts as a plane ofweakness. The plane of failure occurs just above the reinforce-ment and the entire system behaves more or less like an unre-inforced slope. This explanation seems to be consistent with theexperimental results of Selvadurai and Gnanendran (1989) andHuang et al. (1994).Fig. 10 also compares the effect of ordinary geogrid and grid-anchor on bearing capacity of strip foundation located on sandslopes in terms of BCR. These results clearly show that the effect ofthe ordinary geogrid was less than that of the grid-anchor. This isbecause of the presence of anchors in grid-anchor reinforcementwhich provides higher pullout strength. On the other hand, theintrinsic merit of grid-anchor comes about by their anchoragestrength or pullout resistance,which can far exceed the direct shearstrength. Thus, it can be concluded that the shape and type of thegeogrid is one of the important factors related to the improvementof reinforced slopes.A similar trend was observed for level sand ground by Das et al.(1994), for sand slope by Yoo (2001) and Lee andManjunath (2000).Also, the variation of BCR with u/B reported by Selvadurai andGnanendran (1989) and El Sawwaf, 2005 for reinforced sand slopeare similar to that obtained from the present investigation. It wasverified that there exist a critical value for u/B at which maximumachievements in bearing capacity was obtained. The reportedvalues differed between 1.0 and 0.5 according to slope geometry,soil condition and number of geogrid layers.