Basal heave analysis of excavations with consideration of anisotropic undrained strength of clay

Abstract

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.