5.3.4 Ou and Hsieh method
Ou et al.（1993）proposed a procedure to estimate excavation⁃induced ground settlement profile normal to the excavation support wall.Their work was based on observation of 10 case histories in soft soils.From these data，they developed a trilinear settlement profile（Figure 5.11）called spandrel⁃type settlement，which presents the maximum settlement very near to the wall.The spandrel type of settlement profile occurs if a large amount of wall deflection occurs at the first phase of excavation when cantilever conditions exist and the wall deflection is relatively small due to subsequent excavation.The data presented in Figure 5.11 is normalized settlement，δv／δv（max），whereδv（max）is the maximum ground surface settlement，versus the square root of the distance from the edge of the excavation，d，divided by the excavation depth，He.
Figure 5.11 Shape of“spandrel”settlement profile（After Ou et al.，1993）
Hsieh and Ou（1998），based on nine case histories worldwide，extended the work done by Ou et al.（1993）by proposing the concave settlement profile（Figure 5.12）induced by deep excavations.From Figure 5.12，it can be seen that the maximum settlement occurs at a distance of He／2 from the wall and that the settlement at the wall can be approximated to 0.5δv（max）.The case history data also showed that the extent of the primary influence zone is approximately two excavation depths（2He）and after a distance of 4He，the settlement is basically negligible.
Figure 5.12 Proposed method for predicting concave settlement profile（After Hsieh and Ou，1998）
Hsieh and Ou（1998）also established the relationship of cantilever area and deep inward area of wall deflection，similar to the one proposed by O’Rourke（1981），as the first approximation to predict the type of settlement profile.They suggested the following procedures for predicting the settlement profile：
①predict lateral deformations using finite element or beam on elastic foundation methods；
②determine the type of settlement profile by calculating the areas of the cantilever and inward bulging of the wall displacement profile；
③estimate the maximum ground surface settlement asδv（max）≈0.5δH（max）to 1.0δH（max）；
④plot the surface settlement profile using Figure 5.11 for spandrel settlement profile or Figure 5.12 for concave settlement profile.