Pre-failure behaviour of the tropical clay soils of Dhaka, Bangladesh

摘要

A series of undrained triaxial compression tests has been carried out on the tropical clay soils of Dhaka, Bangladesh. Samples were tested in their natural (undisturbed) state and also after destructuration in order to assess the influence of the natural iron oxide cementing on their strength and stiffness. Tangent shear stiffness decay curves have been used to investigate yield of the bonded structure. Natural samples consolidated at effective stresses below 500kPa show a change in stiffness that can be interpreted as a 'bond yield'. A yield surface can be constructed in stress space to identify the onset of yield of the bonds. The tests also show a clear difference in failure envelope between the natural and destructured samples, confirming the influence of the iron oxide bonding on both stiffness and strength. Natural samples consolidated at effective stresses above 500 kPa do not show a clear bond yield point, suggesting that bond yield has been exceeded during consolidation. However, specimens that do demonstrate bond yield during shear still show a difference in failure envelope between the natural and destructured samples. This suggests that the bond yield point represents only part of the bond breakdown process, and samples that have passed through bond yield will still be affected by the presence of bonds. Therefore, bond breakdown should be seen as a progressive process, rather than a distinct point.