A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering, School of Engineering and Technology

Thesis (M.Eng.) - Asian Institute of Technology, 1990

This thesis illustrates stress path studies on soft clays under embankments and in excavations. The stress path followed by a soil element depends on which zone it is located, and the geometry of the embankments or excavations. Along the centerline underneath the embankment, the total stress path followed by a soil element in the weathered crust is much of lesser slope than the Ko-line in the (q {u2022} ,p) plot. The total stress path for a soil element in the very soft clay layer is above the Ko-line in the (q {u2022} ,p) plot and deviates from the standard triaxial stress path used in conventional tests. The total stress path followed by a soil element in the soft to medium stiff clay layer followed by a soil element is along the Ko-line. For points outside the embankments, the total stress paths are shown as the extension loading type. When the ratio of the base width of the embankment to the soft soil layer thiclrness is greater than 2, the total stress paths followed by a soil element in the soft clay layer is along the Ko line. The one-dimensional loading condition can be used for the long term settlement analysis. In the case of excavations, the total stress paths followed by a soil element in the very soft clay layer along the centerline describes an unloading extension state. It is found that the triaxial test can not simulate the stress paths for points under the slope excavation. The triaxial unloading extension test can simulate the stress paths for points under the vertical excavation. Adjacent to the vertical surface of the excavation, the stress path followed by a soil element can be simulated by the triaxial unloading compression test. In view of the stress path followed by a soil element depends on which zone it is located, the finite element analysis should incorporate the soil parameters as described from the appropriate laboratory or field test which closely simulates the stress path followed by the soil under the field condition.