Assessment of engineering properties of Bangkok clay

Abstract

Due to the effect of structure, Bangkok clay is stable in a metastable state. Its void ratio, e, is the summation of the void ratio sustained by the intrinsic fabric, eR, and the additional void ratio due to the structure, es. The intrinsic state line (eRversus log σ′v, where σ′vis the effective vertical stress) is developed in terms of the void ratio at the liquid limit, eL. At the post-yield state, esis inversely proportional to σ′v. The residual additional void ratio, esr, which cannot be eliminated by the increase in effective vertical stress, is constant at about 0.20 for soft Bangkok clay and 0.12 for medium stiff Bangkok clay. From these findings and the ideal condition of zero compression at the pre-yield state, the field yield stress and field compression curve can be assessed. The undrained shear strength is directly related to the field yield stress, since both reflect the structure. The soil structure does not significantly influence the permeability. The permeability of the clay in structured and destructured states is identical under the same void ratio and can be determined from the generalized state parameter, e/eL. These observations result in a simple and practical method for assessment of the engineering properties of natural Bangkok clay.Key words: Bangkok clay, destructured state, compression, intrinsic state line, permeability, structured state, vane shear strength.