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Both excavation and backfilling processes werecompleted in eight steps with same lift thickness of excavation orbackfilling in each step. Therefore, the lift thicknesses were 1.5 mfor the 12 m walls and 0.75 m for the 6 m walls. Figs. 6a and 7ashow the results of DD cases for the 12 m and 6 m walls, respec-tively. Fig. 6b and 7b show the results of DL cases for the 12 mand 6 m walls, respectively.Figs. 6 and 7 show that wall displacements increase as the exca-vation depth or backfill height increases, as expected. During thefirst two stages of the excavation cases, the wall is primarily af-fected by the global rotational movements of the soils around thewall. These global movements are caused by the unbalanced verti-cal soil stresses from the large area loading behind the wall. Theglobal soil movements are rotational movements and cause thetop of the wall move backwards and the tip of the wall move for-ward. When the anchor is installed after the second excavationstage, the wall rotations start to occur at the anchor level due tothe restricted wall movements.During the initial two stages in backfill cases the wall move-ments occur as almost rigid body rotations at the base, because of a small penetration depth and limited horizontal forces actingon the wall. The top of the wall moves outward if foundation soilsare stronger while the top moves backward if weaker foundationsoils are present, because of the global soil movements. Similarto the excavation cases, the wall starts to rotate at the anchor leveldue to the restricted wall movements after the installation of ananchor. The top of the wall at the end of the backfill constructionmethod moves backward for 9-m and 12-m-high walls. The topof the wall moves outward in 6-m-high walls, regardless of thebackfill and foundation soil type.Two major observations obtained from the analysis of walldeformation results shown in Figs. 6 and 7 are: (1) Significant wallmovements occur during the last stage of excavation cases. Almost50% of maximum wall deformations take place during this laststage of excavation. In the backfill cases, on the other hand, the dis-placements gradually increase through the construction stages. (2)The walls constructed by the backfill method have more deforma-tions at the end of construction. The effect of construction methodis magnified when weak foundation soils are present.Maximum wall deformations and location of maximum defor-mations obtained from the analysis of all 12 cases for excavationand backfill cases are shown in Fig. 8a and b, respectively. Fig. 8ashows that wall constructed by the backfill method results in high-er wall deformations compared to excavation method. The effect ofconstructionmethod is much higher when weaker foundation soilsare present at the site. While the walls constructed by the backfillmethod result in approximately 25% higher maximum wall defor-mations in medium dense foundation soil conditions, the differ-ence is approximately 71% for relatively loose foundation soilconditions. Maximum wall displacements generally occur at lowerelevations in backfill cases compared to excavation cases (Fig. 8b)
.Fig. 9 shows the effect of construction method on wall tip defor-mations for the cases analyzed. The effect of construction method is much more significant for the wall tip deformations. The sheetpile tip movements in backfill cases are approximately five timeshigher than in the excavation cases for weak foundation soil condi-tions (Fig. 9). This may be an explanation for some of the wall fail-ures reported in the literature where soft soils below the wall werepresent and wall tip moved outward significantly during backfill-ing operation [17–19], and causing catastrophic wall failures insome cases. For the cases with medium dense foundation soils, 4.3. Wall bending momentsThe bending moments in sheet pile walls throughout the con-struction stages are shown in Fig. 10 for two 12-m-high wallsand in Fig. 11 for two 6-m-high walls. Figs. 10a and 11a showthe results of DD cases, while Figs. 10b and 11b show the resultsof DL cases. The analysis results show that there are significant dif-ferences in bending moments between the excavation and backfillcases. The differences are observed in the development rates ofbending moments during the construction stages, final bendingmoment shape along the piles, magnitudes of positive and negativemoments, and the maximum bending moments.In excavation cases, the bending moment development rate wasslower at the initial stages of construction and much higher at laterstages. For example, both bending moment shape along the walland maximum moments changed significantly during the finalexcavation stage. In the backfill cases the rate of development ofbending moments in the wall was more gradual.The construction method had also an effect on final wall bend-ing moment shapes. While none of the backfilled walls had a posi-tive moment close to the tip of the wall at the end of theconstruction, higher walls (all of the 12-m-high walls and someof the 9-m-high walls) constructed by the excavation methodhad a positive bending moment close to the pile tip. In addition,the ratio of the wall maximum bending moment to the bendingmoment at the anchor level is much higher in backfill cases com-pared to excavation cases. The ratio can be as low as 1.08 (DD12case) in excavation cases with high walls, i.e. the bending moment at the anchor level is very close to the maximum bending momentOn the other hand, the lowest ratio obtained in backfill cases was2.57 (DL12 case) while ratios up to 5.12 (DD6 case) were observedfor walls with relatively lower heights, i.e. bending moments at theanchor level is much smaller than the maximum wall bending mo-ments in the wall.The most important observation regarding the bending mo-ments obtained from the analyses of all 12 cases studied was thatthe backfill cases always resulted in highermaximumwall bendingmoments. The comparison of excavation and backfill methods onthe wall maximum bending moment and its location for all 12cases analyzed are shown in Fig. 12. Fig. 12a shows that walls con-structed by the backfill method result in approximately 34% highermaximum bending moments compared to the walls constructedby the excavation method.