In this research, normally and overconsolidated undrained of Nakdong river clayey silt in triaxial compression tests were performed on specimens of 72% silt with 19.5% clay content. In CIU tests, the samples were normally isotropic consolidated from 100 to 400kPa and unloaded to 200kPa for OCR=2, unloaded to 100kPa for OCR=4 and unloaded to 50kPa for OCR=8 in overconsolidation before shearing. In CIU-NC tests, deviator stresses of normally consolidated clayey silt were observed softening tendency with increasing dilatancy and lowcohesion after failure. Peak pore water pressures decreased under increasing initial confining pressures. In CIU-OC tests, deviator stresses decreased and exhibited softening tendency after failure. Porewater pressure decreased with increasing OCRs during shear. Clayey silts tend to dilate and change in pore water pressure of OCR=8 become negative due to decreasing final effective stress.
In this paper, to study the undrained shear behaviors of normally and overconsolidated Nakdong river soils, a series of standard triaxial tests were performed on isotropically consolidated remolded soil specimens. The test results indicate that the stress-strain relationship is nonlinear, the peak shear strength develops at intermediate axial strain, and the critical state shear strength (corresponding to no volume change during shearing) develops at large axial strains after failure. If the pore pressures decrease to values below the vapor pressure of water, cavitations occurs and bubbles of air liberate from the pore water (Brandon and Andrew 2006). When this happens, shear does not occur at constant volume but the specimens exhibit no volume change at critical state in shearing under loading. There is no doubt that triaxial compression test is presently the most widely used procedure for determining strength and stress-strain properties of soils. The behavior of clayey silt is more difficult to characterize than the behavior of clay or sand, because of the tendency of clayey silts to dilate during shearing (Yamamuro and Kelly 2001).
