Doctor of Philosophy (PhD)


Civil and Environmental Engineering

Document Type



Recent advances in laboratory instruments and techniques enabled researchers to explore new aspects of the behavior of geomaterials and perform measurements that would be otherwise impossible to acquire using traditional geotechnical laboratory techniques. This dissertation is focused on utilizing elastic and electromagnetic wave measurements and SMCT imaging to non-destructively characterize different aspects of the behavior of unsaturated soils. A model that relates P-wave velocity in soils to the volumetric water content was used to develop a new methodology to determine the in situ density and moisture content of soils. It was numerically and experimentally verified to assess it validity and range of applicability. On the other hand, a triaxial apparatus that enables the measurement of P- and S- wave velocities in unsaturated soil specimens under controlled net stress and matric suction was also developed. Several verification experiments were performed using the apparatus and the results were compared to theoretical models as well as previous experimental results. Moreover, a drying cell was used to examine the effect of the presence of fine clay and silt particles on the elastic waves` velocity and the small strain stiffness of unsaturated soils. The results were confirmed by analyzing SMCT images of similar samples at different drying stages. The proposed methodology yielded good predictions of the density and the moisture content of soils. However, different experimental and numerical error sources caused the predicted density and moisture content values to slightly differ from the measured values. For the majority of the tested specimens, the density was estimated within ±10% of the measured values while the water content was estimated within ±20%. On the other hand, the experimental results from the new triaxial apparatus showed a significant effect of matric suction on the recorded wave velocities. It was also documented that wave velocity values increase with increasing percentage of fine silt particles in the specimens. The results of the drying cell experiments as well as the SMCT image analysis showed the profound effect of the presence of fine silt and clay particles on the small strain stiffness of unsaturated soils. The density of the pore fluid increased during drying due to the higher fine concentration. The concentration of fine particles was found to be significantly higher at areas close to the interparticle contact than in pore bodies away from the contacts causing an increase in the interparticle contact stiffness.



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Committee Chair

Khalid Alshibli