A thesis submitted in partial fulfillment of the requirements for the Degree of Master of Engineering at the Asian Institute of Technology, Bangkok, Thailand

Thesis (M.Eng.) - Asian Institute of Technology, 1969

An investigation was carried out on undisturbed samples of the Stiff Bangkok Clay taken from an average depth of 38 feet at the new campus of the Asian Institute of Technology at Rangsit, 40 kilometers north of Bangkok. Conventional isotropically consolidated undrained triaxial compression tests with pore pressure measurements were used in the investigation. The soil samples tested were grouped into two series. In the first series, the samples were consolidated at the confining pressure to be used in the particular test. In the second series, the samples were first consolidated at a maximum past pressure of 90 lb per sq in., and then allowed to swell under various lower consolidation pressures prior to shear. The test results show that the Stiff Bangkok Clay is an overconsolidated clay with a maximum past pressure of about 60 lb per sq in. The overconsolidation has been attributed to desiccation. It was observed that in the normally consolidated range, a unique normalized stress strain relationship was indicated. In the overconsolidated range, the relationships were dependent upon the overconsolidation ratio. The overconsolidation ratio also influenced the effective stress path, undrained shear strength and pore pressure parameter A. The trends indicated by the results of Series II were very similar to those indicated by Series I with some differences in magnitudes of the results due to the different maximum past pressure. The behavior of the overconsolidated clay was explained in the light of diagenetic bonds developed during overconsolidation. Comparison of the results with those obtained on other clays indicated that the behavior of the Stiff Bangkok Clay was similar to that of the other clays. It was noted that for any particular overconsolidation ratio the Stiff Bangkok Clay appeared to have a relatively high undrained shear strength. Also the corresponding value of pore pressure parameter at failure was not as low as for most other clays.