Estimation of undrained shear strength anisotropy for over-consolidated cohesive soils

Hirofumi TOYOTA

The stresses in the ground have acted from the various directions when the structures, embankments and retaining walls are constructed on the real ground. In addition, the consolidation stress ratio, K, or the over consolidation ratio are different in each point. Therefore, it is important to use the shear strength corresponding to the stress state of each point for the stability analysis because the stresses of ground induced by the structures are different in each point. Then, Bjerrum et al. proposed the experimental methods to estimate the real ground strength, and it has been confirmed that the different undrained shear strength are obtained from the various shear tests. Thus, it is important to examine the practical evaluation method of undrained shear strength.
The hollow cylinder torsional shear apparatus was used for proposing the evaluation method of undrained shear strength using anisotropically over-consolidated cohesive soils with the various directions. The experiments were also carried out under plane strain conditions for two-dimensional problems.
The main results are summarized as follows:
1. As the effect of over consolidation ratio on undrained shear strength, it was confirmed that the undrained shear strength increased linearly with the over consolidation ratio, and the strength of OCR 6 is three times higher than that of OCR 1 by the generation of pore water pressure.
2. The similar tendency with above mentioned was also observed under the undrained plane strain condition.
3. As the effect of the K-value on the undrained shear strength, the strength increased with a decrease in the K-value under the ?กว=0. However, this tendency became the opposite under the ?กว=90.
4. The proposed equation enabled to estimate undrained shear strength under the real stress state from the undrained shear strength obtained from the triaxial compression test.

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