| Pore pressure increases in soil deposits due to an earthquake results in hydraulic gradients and associated pore fluid flow during and after earthquake shaking. Stratifications affect the pore fluid flow due to the permeability contrasts. This can result in void redistribution with certain zones getting loosened and others getting densified. Thus, soil properties can change during and after shaking making it difficult to estimate a design shear strength based on pre-earthquake soil properties. The potential for strength reduction due to void redistribution is not taken into account directly in the current procedures used to estimate the design shear strength for soils with susceptibility for liquefaction. This is due to the uncertainty, disagreement, and poor understanding in the profession about the role of void redistribution in the field.; This thesis reports part of a study conducted at the University of California, Davis to study the effects of void redistribution on liquefaction behavior of layered slopes. The studies carried out included (1) documenting evidences of void redistribution from past model tests and case histories, (2) performing a series of dynamic centrifuge tests of sand slope models with silt seams and analysis of the test results, (3) numerical and dimensional analysis studies to understand the influence of different factors on the amount of void redistribution, and (4) the development of a framework of understanding about the mechanism of void redistribution based on the principles of soil mechanics.; Localization of shear strains and resulting large slope movements observed in the sand—bottom of silt interface in some centrifuge model tests, under the combined presence of certain factors, is attributed to the loosening of that zone by void redistribution. Experimental and numerical studies indicate that several parameters such as initial relative density of sand, volume of sand below the silt arc, shaking duration, seismic history, permeabilities, stratigraphy, and geometry can influence the amount of loosening due to void redistribution. These findings underline the need to further study the mechanism of void redistribution and come up with methods to explicitly account for it in engineering practice. |
