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(2)where:Phi: resultant thrust measured at loadcell i (i ¼ 1–10).For both types of wall, values of Kf increase with decreasing kv atthe moment of wall completion (He/H ¼ 1.0), and also at themoment of full surcharge (He/Hj1.5). In the case of kv ¼ 1.3 kPa/mm for CWs, Kf is greater than Ko, indicating that additionalcountermeasures should be taken to alleviate the influence ofexcessive earth pressure against the facing of a conventional wall on a deformable ground. This is not the case when GRS-RW isplaced on ground with a similar deformability, as illustrated inFig. 16b. These results strongly suggest ‘earth pressure relief’characteristics of GRS-RW due to the reinforcing layers inthe backfill. This advantage may be a result of the restrainingmechanism of the reinforcing layers. Measurements of tensilereinforcement forces in these tests and their implication to theperformance-based design of GRS-RWs on deformable groundswillbe reported in the future.Figs. 17a,b show distributions of local lateral pressure coeffi-cients (Kf,z) against the wall at the completion of surcharging forCWs and GRS-RWs, respectively, placed on various deformablefoundations. Kf,z, is defined as:Kf ;z ¼ Phiðg,Ziþ qÞ,Svi(3)where:Zi: depth of reinforcement layer i.Svi: tributary vertical spacing of reinforcement layer i.For CWs placed on a foundation of kv ¼N, Kf,z/Ka ¼ 1.0 wasfound for almost the full-height of the backfill. This situationgradually changed as the value of kv decreased. The most criticalcondition occurred for the case of kv ¼ 1.3 kPa/mm (the mostdeformable foundation in this study), in the sense that values ofKf,z/Ka approximately follow the line of Ko/Ka (Ko ¼ 1 sin 4; Ko, at-rest lateral pressure coefficient), while with a distinctively largevalue of Kf,z/Ka at lower 1/3 of the wall. This is consistent with thefinding discussed earlier for which the case of kv ¼ 1.3 kPa/mmcaused a tilting-backward mode. As a result, a passive lateralpressure state may exist at the lower 1/3 of the wall. Values of Kf,z/Ka for GRS-RWs, shown in Fig. 17b, all show the condition of Kf,z/Ka 1.0 for amajor part of thewall height, with small exceptions inthe lower 1/3 of the walls on kv ¼ 1.8 and 1.3 kPa/mm. This is alsodue to the tilting-backward displacement of the facing. Fig. 17b alsoshows that the lower 2/3 part of the wall shows similar trends andmagnitudes of Kf,z to those reported by Won and Kim (2007) ona full-scale GRS-RW placed on a deformable foundation. Theinconsistency of the measured Kf for the upper 1/3 of the wallbetween the data obtained here and those reported by Won and Kim (2007) may be due to the internal soil stress induced by thewet-and-dry cycle in the crest of the exposed full-scale wall, whichis beyond the scope of the present study.5. ConclusionA comparative study on the settlement-tolerating behavior ofsoil retaining walls situated on non-deformable and deformablefoundations was performed using 0.5 m-high (H ¼ 0.5 m)cantilever (CW) and geosynthetic-reinforced soil retaining walls(GRS-RW) with similar factors of safety against sliding. The plane-strain model walls were backfilled with a uniform 1.96 mm-diameter,150 mm-long stainless steel rod assembly,with a uniformunit weight of 68.5 kN/m3, to simulate a 4-g condition of the modelwall or simulating the stress level of a 2 m-high wall. The followingconclusions were obtained:(1) Among the four investigated ground-stiffnesses (kv ¼N, 3.6,1.8, and 1.3 kPa/mm) that generated maximum foundationsettlements of Smax/Hj0, 0.25, 5, and 10%, the case ofkv ¼ 1.8 kPa/mm (Smax/Hj5%), rather than the case ofkv ¼ 1.3 kPa/mm (Smax/Hj10%), generated the maximumvalues of q, Dh, and Dv1. This is valid for both CWs and for GRS-BWs investigated here. It was found that a tilting-backwarddisplacement mode of the facing for both CWs and GRS-BWsoccurred at Smax/Hj10% accounts for the small tilting anddisplacement observed above. An increase of passive resistancein front of the wall due to a greater wall settlement may alsoaccount for the increase of wall stability in the case ofkv ¼ 1.3 kPa/mm (Smax/Hj10%).(2) The stability of GRS-RWs in terms of tilting angle (q), horizontaldisplacement (Dh), and settlements of the crest of the backfill(Dv1) measured during construction and surcharging processeswas less influenced by the increase of foundation settlements,when compared with that for CWs. A GRS-RW with a moder-ately high safety factor against sliding (Fs ¼ 2.90 withoutsurcharge, or q ¼ 0 kN/m2) exhibited excellent ductility intolerating foundation settlement, in the sense that displace-ments and tilting of the wall are insusceptible to a foundationsettlement up to Smax/Hj10%.(3) Better performance of GRS-RWs than CWs, in terms of the totallateral thrust on the facing (or lateral pressure coefficient, Kf),was observed. It was shown that under similar foundationstiffness, the values of Kf for GRS-BWs were always smallerthan those for CWs. In addition, values of Kf for GRS-BWs wereless susceptible to changes of kv than those for CWs.(4) Measured local values of lateral pressure coefficients (Kf,z), ata certain depth (z) along the facing of CWs, attained the at-reststate (Ko) for the central 1/3 of the wall when situated ondeformable foundations with kv ¼ 1.3 kPa/mm (or Smax/Hj10%). A passive state exist for the lower 1/3 of the wall inthe case of CW on kv ¼ 1.3 kPa/mm. This indicates that theseverity of the CW placed on a deformable foundationincreases as the value of kv decreases, from the standpoint ofglobal and/or local lateral pressure against facing.(5) Measured local values of Kf,z along the facing of GRS-RWs aresubstantially lower than Coulomb’s active pressure coefficient(Ka) for the upper 2/3 of the wall, and are insusceptible tofoundation stiffness changes. This observation has minorexceptions in the cases of kv ¼ 1.8 and 1.3 kPa/mm, with valuesof Kf,z slightly larger than Ko, reflecting a localized at-rest statearound the toe of the facing of the GRS-RW.To develop relevant limit-equilibrium-based designmethods forCWs and GRS-RWs placed on deformable foundations, knowledgeof lateral pressure coefficients associated with various displace-ments and rotations induced by the foundation settlement arerequired. It is also noted that the wall behavior and conclusionsobtained here may be influenced by the thickness of uniformfoundation layer immediately below the wall