Stress-strain behaviour and strength characteristics of lightly overconsolidated clays | |
| Author | Kim, Seung Ryull |
| Call Number | AIT Diss. no. GT-90-2 |
| Subject(s) | Strength of materials Soil consolidation |
| Note | A dissertation submitted in partial fulfillment of the requirements for the Degree of Doctor of Engineering, School of Engineering and Technology |
| Publisher | Asian Institute of Technology |
| Abstract | The path dependent stress-strain behaviour and strength characteristics of Soft Bangkok clay in the normally and overconsolidated states are studied both under isotropic and Ko pre-shear consolidation conditions in compression and in extension. The experimental programme included triaxial consolidation and swelling tests (both isotropic and Ko-consolidation and swelling) as well as four series of undrained triaxial tests (three of them are in compression and one in extension) and ten series of drained tests. Following the Hvorslev approach, the initial pre-shear void ratio of all the samples is kept constant to about 1.16. The review of the literature is presented in two chapters, one emphasizing the Koconsolidated behaviour of clays and the other on the Critical State stress-strain theories both with 'associated' and 'non-associated' flow rules. Critical comments are made at the end of each chapter. The undrained behaviour of the Soft Bangkok clay is described in one chapter where all the test data are presented in a suitable form for evaluation of undrained soil parameters. In a broad sense, the data confirm the unique State Boundary Surface, the associated Critical State Line and the Hvorslev failure envelope. They also confirm the existence of a set of constant q yield loci for undrained distortional strains within the State Boundary Surface and on the wet side. A radial fan of undrained shear strain contours is obtained on the dry side. Pore pressure-stress ratio relationships are established to determine the undrained stress path and the excess pore pressure. Volumetric yield points constituting the volumetric yield locus which lie on the State Boundary Surface are determined for the samples when the stress states reach the State Boundary Surf ace. The drained behaviour of the Soft Bangkok clay is then introduced in the following chapter. The drained behaviour also confirms a unique State Boundary Surface with the associated Critical State Line and the Hvorslev failure envelope. The region within the State Boundary Surface is divided into three zones based on plastic volumetric yielding. In one zone, the volumetric strain is purely elastic and is close to the isotropic axis. In the second zone on the wet side, compressive plastic volumetric strains take place, while in the third zone dilational plastic volumetric strains occur. A flow rule is then established which will merge with the flow rule of the Modified Cam Clay Theory of ROSCOE and BURLAND (1968) for stress states on the State Boundary Surface and which shows a reduction in the plastic dilatancy ratio with a decrease in the mean normal stress at any one stress ratio. Comparisons of the experimental observations with predictions from the Critical State theories reveal that the Revised Cam Clay Theory of ROSCOE and BURLAND (1968) makes successful predictions for srress states on the State Boundary Surface, while Pender's Model -111- (PENDER, 1977, 1978) gives approximate predictions for stress states within the State Boundary Surface. Dafalias' Model (DAFALIAS, 1987) is found to be more suitable for the anisotropic stress-strain behaviour when the stress states lie on the State Boundary Surface. For the region inside the State Boundary Surf ace, a Carn Clay (SCHOFIELD and WROTII, 1968) type of yield locus is established to calculate plastic volumetric strains on the wet side of the Critical State. The plastic volumetric strain so obtained is used with the flow rule established to determine the plastic shear strains due to volumetric yielding inside the State Boundary Surf ace. The contribution from the constant q yield loci is then added to make the full value of the plastic shear strains on the wet side of the Critical State. On the dry side, however, the plastic volumetric strains are obtained from a set of dilational volumetric yield loci. These yield loci, when combined with the flow rule (as established for the wet side but with a negative magnitude), enable the distortional strains due to dilational plastic volumetric strains. The undrained shear strain increments on the dry side as determined from the radial fan of constant shear strain contours are then added to the distortional strain increment obtained from the volumetric yield loci to make the full value of the shear strain increments. Finally, comparisons are made within the State Boundary Surface for the pore pressures and strains from the Author's Model with the experimental observations. |
| Year | 1991 |
| Type | Dissertation |
| School | School of Engineering and Technology (SET) |
| Department | Other Field of Studies (No Department) |
| Academic Program/FoS | Geotechnical and Transportation Engineering (GT) |
| Chairperson(s) | Balasubramaniam, A.S. ;Honjo, Yusuke |
| Examination Committee(s) | Karasudhi, Pisidhi ;Bergado, Dennes T. ;Noppadol Phien-wej ;Burland, J. B. |
| Scholarship Donor(s) | The Government of Japan |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 1991 |