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The value of fb ¼ 18 for CW is based on the average value of friction angle measured atthe base of the CW which is similar to the steel rod–steel plateinterface friction angle obtained in a direct shear test. The value offb ¼ 22 is also based on a tilting table test for the reinforcement–steel rod interface; the steel rod–steel rod friction angle is based onthe direct shear test reported by Huang and Luo (2009),assummarized in Table 3.3. Behavior of soil retaining walls situated onnon-deformable and deformable foundationsFigs. 6a,b show measured settlements of the foundation ata level of 100 mm below the wall base of the CW and GRS-BW,respectively. For a similar value of kv, the curves of the foundationsettlement for the CW and GRS-BW are similar in magnitude andshape as a result of the self-weight of the backfill and the surcharge.It can also be seen that far from the toe, the ground settlementapproaches a uniform state. A significant differential settlement exists around the toe of CW and GRS-BW, reflecting the abruptchange of the self-weight and surcharge loads across the toe of thewall.Fig. 7a shows the developed shear bands in the backfill of CWsituated on the ground of kv ¼NkPa/mm and subjected toa surcharge q of 17 kN/m2. A pair of shear bands, both with an angleof 63 to the horizontal, can be observed. These shear bands areapproximately in the direction of the maximum stress obliquity(equal to 45 þ f/2 ¼ 62.5 ). Fig. 7b shows the shear band and walldisplacements for the wall shown in Fig. 7a. It can be seen thata maximum vertical settlement at the top of the wall, 2.4 mm (Dv/H ¼ 0.0048), was measured in this case; it was induced by thedeformation of the 100 mm-thick backfill above the rigid founda-tion. A foundation settlement of this order can be deemed as a caseof the unyielding subgrade condition.Figs. 8a,b show shear band development and displacements,respectively, for a CW placed on a foundation of kv ¼ 1.8 kPa/mm.More intensively sheared backfill and greater vertical and hori-zontal displacements of the wall induced by a greater foundationsettlement as compared to those shown in Figs. 7a,b, can be seen.Note that the settlements and displacements shown in thesefigures were amplified for better visibility. Figs. 9a,b showthe shearbands and displacements of a CW placed on the ground ofkv ¼ 1.3 kPa/mm (the lowest value of kv in the present study, Smax/Ht j10%). It is noted that the number of shear bands significantlydecreased compared to the case of kv ¼ 1.8 kPa/mm. A verticalsettlement of the wall, Dv ¼ 9.2 mm (Dv/H ¼ 0.018), and maximumvalues of Smax/H ¼ 0.072 and 0.094 are all greater than thoseobserved in previous cases. However, themaximumwall horizontaldisplacement of the wall, Dh ¼ 6.1 mm (Dh/H ¼ 0.012), is smallerthan those of cases using kv ¼ 3.6 and 1.8 kPa/mm. This suggests that a greater foundation settlement does not necessarily introducea greater horizontal displacement of the CWor aworse condition ofthe backfill in terms of the integrity (or intensity of shear bands).This occurs because a large settlement of Smax/Hj10% facilitatesa tilting-backward mode, inhibiting active failures in the backfill.An increase of passive resistance in front of thewall due to a greaterwall settlementmay also account for the increase ofwall stability inthe case of kv ¼ 1.3 kPa/mm (Smax/Hj10%). This issue was firstdiscussed by Huang and Luo (2009).Figs. 10a,b show the shear band development and displacementof facing for a GRS-BW placed on an unyielding foundation. Alongwith very limited wall displacements, an intact backfill zone evenunder a fully loaded condition of q ¼ 17 kN/m2can be observed.Figs. 11a,b show the case of GRS-BW situated on the ground ofkv ¼ 1.8 kPa/mm. The wall displacements and foundation settle-ment increase to some extent in response to a decreased subgradereaction coefficient from the previous case of kv ¼ 3.6 kPa/mm.Only a pair of shear bands appeared. A contrast in the response tofoundation yielding can be seen by comparing Figs. 8b and 11b. Theoverall ductility of GRS-BW, which may be a result of backfill-reinforcement interaction, can be observed. Fig. 11b shows that theshear band that developed on the left side of the backfill is probablydue to a small rotation on the left-end of the foundation slab and isirrelevant to the integrity of the backfill.