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, 1972

The effect of maximum past consolidation pressure and aging on diagenetic bonds was investigated. The maximum consolidation pressures of 120, 700 and 1400 lb/in2 were used and .the effect of aging was studied by consolidating the samples under a consolidation pressure of 120 lb/in2 for a period of 4 weeks. The soil used in this investigation was an artificially sedimented clay. Natural Bangkok clay and Bentonite were sedimented in salt water having a salt concentration of 35 gm/liter. ·Sedimented Bangkok clay was- used to study the· effect of maximum past consolidation pressure on the bonds while sedimented Bangkok clay and Bentonite were used for studying the effect of aging: on the bonds Isotropically consolidated undrained tests with pore pressure measurement were performed throughout the investigation. The high consolidation pressure tends to break the bonds at the contact points resulting in a· low. strength and a small amount of stored energy. The effect of aging ·was to increase the bond strength as well as to make the bonds more brittle. In overconsolidated clay, at the same OCR the sample with the higher past consolidation pressure stored a lesser amount of strain· energy and hence it exhibited a lower tendency to dilate during shear. The amount of strain energy stored in the overconsolidated soil in aged samples as compared with samples without aging depends on the rigidity of the bonds. At very high ·values of OCR the number of bonds present in the sample was very small resulting in a relatively low shear strength and .low tendency to dilate.