Doctor of Philosophy
Civil and Environmental Engineering
M. Hesham El Naggar
The shear wave velocity (Vs) and shear modulus (G) are important parameters that are required when dealing with a variety of geotechnical problems covering a wide range of shear strain in a soil medium. Different laboratory tests can be used to measure Vs and G such as resonant column, bender element and cyclic triaxial tests. However, these tests have several limitations in terms of stiffness of the test specimens and range of shear strain that can be applied to them. The importance of Vs in geotechnical engineering and the shortcomings of existing testing devices for its measurement have motivated this research. Innovative piezoelectric ring actuators (PRA) devices were fabricated and were incorporated in oedometer and triaxial apparatuses to measure Vs for different types of soils.
The PRA device incorporated in a conventional oedometer apparatus facilitated measuring Vs simultaneously with 1D consolidation testing of sand and clays. The performance of the developed PRA setup was evaluated and verified through comparing measured Vs of Ottawa sand with results available in the literature and those obtained from bender element testing. Effects of initial state/void ratio, applied pressure, mean particle size, along with percentage of non-plastic fines on Vs of Ottawa sand were investigated using the PRA setup. Cohesive soils (natural and reconstituted) were tested in oedometer and static triaxial tests. The results from oedometer, static triaxial along with Vs measurements were utilized to produce useful correlations for Vs with some standard soil parameters such as soil compressibility index, Cc, and undrained shear strength, Su. In addition, the measured small strain stiffness (Edynamic), large strain static triaxial stiffness (Estatic) and oedometric stiffness (Eoedometer) were used to establish the range of dynamic to static stiffness ratios Edynamic/Eoedometer, and Edynamic/Estatic.
The PRA device incorporated in the cyclic triaxial apparatus was employed to test six different sensitive and in-sensitive cohesive soils. Vs and G were measured using the cyclic triaxial test and the PRA device at different strain amplitudes. The results were utilized to produce dimensionless correlations for Vs and G for cohesive soils. The measured Vs using the PRA device incorporated in a conventional triaxial apparatus along with the developed correlations can then be utilized to reliably estimate the shear modulus reduction curve of cohesive soils without performing cyclic triaxial tests.
Ahmad, Saeed, "Piezoelectric Device for Measuring Shear Wave Velocity of Soils and Evaluation of Low and High Strain Shear Modulus" (2016). Electronic Thesis and Dissertation Repository. 3490.