|M.Sc Student||Mehr Arilon|
|Subject||Saturated Sand Behavior during Earthquakes|
|Department||Department of Civil and Environmental Engineering||Supervisor||Professor Emeritus Sam Frydman|
The research deals with pore water pressure generation during cyclic loading.
When loose sand is subjected to a drained change in the deviatoric component of the stress matrix, it tends to contract its volume. When the loading is undrained, the isotropic component results in reduction of the effective isotropic pressure or pore water pressure generation.
However, monotonic pure deviatoric, drained compression, triaxial tests show that there is only a minor densification of the sand structure.
This behavior leads to two significant conclusions:
A. An arbitrary change in the deviatoric stress matrix does not necessarily induce volume reduction in drained conditions.
B. The triaxial test does not simulate what happens in the site during earthquakes and should not be used in order to predict the development of pore pressure and liquefaction hazard of sand.
These conclusions led to the search for a new model to predict pore water pressure generation, based on analysis of cyclic, hollow cylinder, torsional shear tests.
The Phase Transformation Point was set to be the reference point on which the new model is based. This Point in terms of Von Mises stress criterion was found to be a logarithmic cut off function of the current effective isotropic stress.
A new model, which predicts the incremental pore pressure generation during the whole process of cyclic torsional loading, was developed.
In order to complete a closed model, which includes prediction of shear strains, it was found that the logarithmic curve, with a modification which takes account the effect of pore pressure generation on the maximum shear modulus, as well as use of Masing rules for cyclic loading, provides the best fit to the experimental results.