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UBC Theses and Dissertations

The verification of relationships for effective stress method to evaluate liquefaction potential of saturated sands Bhatia, Shobha K.


The constitutive relationships proposed by Finn, Lee and Martin (1977) for the effective stress analysis of saturated sands during earthquakes are studied. The basic assumptions of their porewater pressure model appears to be well founded. There is a strong verification of a unique relationship between volumetric strain in drained tests and pore-water pressures in undrained tests for both normally and overconsolidated sands. An important point to emerge from this study is that the rebound modulus used in converting the volumetric strains to porewater pressures should be measured under dynamic conditions. The porewater pressure model predicts successfully the porewater pressure response under undrained conditions for uniform and irregular cyclic strain and stress histories. When the porewater pressure model is coupled with a non-linear stress-strain relationship in effective stress analysis, it predicts realistic porewater pressure response in undrained tests for cyclic stress histories representative of earthquake loading. Results suggest that strain-hardening effects do not occur unless the sand is allowed to drain. A new porewater pressure model based on endochronic theory is presented in which the porewater pressures are directly related to dynamic response parameters. This approach bypasses the need for converting volumetric strains to porewater pressures. The proposed formulation relates porewater pressure to a single monotonically increasing function of a damage parameter. This parameter allows the data from constant strain or stress cyclic loading tests to be applied directly to predict the porewater pressure generated in the field by irregular stress or strain histories due to earthquakes. This formulation is an extremely efficient way of representing a large amount of data and can be easily coupled with dynamic response analysis to perform effective stress analysis. This study is based on extensive experimental data on Ottawa sand, crystal silica sand and Toyoura sand. In total, one hundred and fifty tests were performed for this study. The tests were performed under cyclic simple shear conditions using Roscoe type simple shear apparatus. Dry sand was used for both the drained and constant volume tests conducted for this study. The tests were performed under both stress controlled and strain controlled conditions.

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