There are two general types of settlement profiles induced by excavation, the spandrel type and the concave type. Based on a regression analysis of the field observations of settlement curves with predominantly cohesive subsurface conditions, an empirical method for predicting the spandrel and concave settlement profiles is proposed. The proposed method is verified through several case histories. For comparison, the results obtained from other empirical methods are also presented. The proposed method provides a fairly good prediction of ground surface settlement and yields better prediction of angular distortion than other empirical methods for the concave- and spandrel-type settlement profiles. Furthermore, the relationship of cantilever area and deep inward area of wall deflection is established which can be used as the first approximation to predict the type of settlement profile.Key words: prediction, excavation, settlement profile, spandrel, concave.
The objective of this paper is to study the characteristics of ground surface settlement during excavation. Ten excavation cases in Taipei with good-quality construction and field observation data are selected to study the characteristics of excavation behavior. The location of maximum lateral wall deflection, magnitude of maximum lateral wall deflection, relationship of maximum lateral wall deflection and maximum ground surface settlement, location of maximum ground surface settlement, and apparent influence range are thus established based on the actual excavation cases. Finally, an empirical formula is proposed to predict the ground surface settlement profile at the center section of an excavation, where the behavior may be characterized by plane-strain conditions. Key words : excavation, surfac settlement, wall deflection, plane strain, empirical formula.
In this study, two cases of excavation to failure were utilized to investigate reasonable analysis methods for basal heave analysis. Three types of tests were carried out to obtain the undrained shear strength of clay in excavations, including the field vane (FV) shear test, the triaxial unconsolidated undrained (UU) shear test, the K0-consolidated undrained axial compression (CK0U-AC) test, the K0-consolidated undrained axial extension (CK0U-AE) test, and the K0-consolidated undrained direct simple shear (CK0U-DSS) test. The analysis results show that the safety factors against basal heave calculated using isotropic undrained strength from the UU test appear acceptable in both excavations, but the results are highly empirical. Safety factors calculated from the FV test tend to be irregular. Moreover, the safety factors were overestimated using the CK0U-AC test results. On the other hand, the safety factors computed using anisotropic undrained strength yielded reasonable results. If we perform simplified anisotropic analysis using the average value of the CK0U-AC and CK0U-AE test results or the undrained strength obtained from the CK0U-AC and CK0U-AE tests utilized in the active and passive sides of the failure surface, respectively, the results will be close to those from anisotropic undrained strength analysis but on the conservative side. Therefore, anisotropic undrained strength analysis and simplified anisotropic analysis are recommended for basal heave analysis.
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