| Summary: | 碩士 === 東南科技大學 === 營建科技與防災研究所在職專班 === 102 === For deep excavations in soft clay, this study estimates the difference between the factor of safety against basal heave determined from the anisotropic undrained shear strength and that determined from the isotropic undrained shear strength. In general, the isotropic shear strength Su,I is equal to Suc and the strength anisotropy ratio of clay Ar ranges from 0.4 to 0.9. When the strength anisotropy ratio of clay Ar is smaller than 0.75, the isotropic factor of safety against basal heave Fs,I is larger than the anisotropic factor of safety against basal heave Fs,A (i.e., Fs,A /Fs,I < 1) with a maximum difference of about 24%. Comparatively, if the strength anisotropy ratio of clay Ar is larger than 0.75, Fs,I is smaller than Fs,A (i.e., Fs,A /Fs,I > 1) with a maximum difference of about 9%. The ratio of Fs,A /Fs,I determined from Su,I = Sud condition is insensitive to the change of Ar. Over the range of Ar = 0.4 to 0.9, Fs,I is smaller than Fs,A by an average of about 15%.
This study uses three different approaches to calculate the factor of safety against basal heave and compare with three field excavation cases. Three different methods are the factor of safety against basal heave proposed by Terzaghi (1943), the isotropic factor of safety against basal heave, and the anisotropic factor of safety against basal heave proposed by Liao and Su (2012). However, the factors of safety are plotted on the chart that suggested by Mana & Clough (1981) for the maximum deformation of retaining wall and the factor of safety against basal heave. The result showed that the factor of safety against basal heave all close or below the lower limit value.
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