Date of Award


Degree Type


Degree Name

Doctor of Philosophy (PhD)


Civil and Environmental Engineering


Dawit Negussey


Confining pressure, Creep deformations, EPS geofoam, Strength and Modulus, Thermal, Yield stress

Subject Categories



EPS geofoam blocks underlying compacted soil and structural loads become subjected to multi-axial loading. Effects of confining pressure on the stress-strain behavior of EPS geofoam have been investigated in previous studies. Some studies found increases in confining stress lead to corresponding decreases in both modulus and compressive strength. Increasing confining stress has also been reported to result in higher compressive strength. Regardless of the sense and attributed significance of the effects of confinement on EPS geofoam behavior, the implied effects on performance are generally not considered in practice. A series of triaxial compression tests were conducted on EPS geofoams of different densities over a range of confining pressures. Results from the investigation indicate increases in confinement lead to decrease in yield stress and post yield compressive resistances, depending on the EPS density and range of confining pressures. The practical significances of confining stress effects are discussed. An approach for incorporating the more significant effects of confining stress on EPS geofoam behavior is considered.

Evaluations of EPS-soil-structure interactions require reasonable representation of stress-strain relationships for numerical modeling. A method proposed in this work uses density of geofoam block and resin material properties to represent the stress-strain response of EPS geofoam. The stress-strain curves obtained from such representation are compared with results from laboratory tests and models by others. The stress-strain curves generated by the proposed method predict very well the relations especially for denser geofoams. A modified hyperbolic stress-strain relationships that can account for confining stress effects is also proposed. The modified hyperbolic model only requires three parameters that can be obtained from triaxial tests. Prediction accuracy of this model is compared with data from triaxial tests which were not part of data sets used to obtain model parameters. Comparison is made with other models proposed by different authors and the stress-strain relationships obtained by this approach predict test data well.

Characteristics of inherent and stress induced anisotropy of EPS geofoam was investigated by triaxial tests conducted on pre-stressed EPS geofoam. Induced anisotropy was observed to reduce the modulus significantly.

A series of creep tests were performed on different densities of EPS geofoam with and without confining pressures. The results showed confining pressures can significantly affect the creep responses of EPS geofoam. Effects of confining pressures on creep deformations were more pronounced for lower densities.

Creep tests were performed in a temperature controlled chamber to evaluate effects of cyclic temperatures. Coupled effects of temperature and creep were studied for different stress levels. Comparisons were made to actual field observations and FLAC model results. Strains and induced stresses from seasonal temperature variations were relatively small.


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