Master of Engineering Science
Civil and Environmental Engineering
Triaxial tests are widely used to determine the behavior and strength characteristics of soils without due attention to the differences in specimen size. Several drained and undrained monotonic triaxial compression shear tests are performed on three different specimen sizes of the same sand to investigate the influence of specimen size and scale effect on the shear behavior. The test results indicate that the behavior of loose sand is strongly influenced by the specimen size, with larger specimens exhibiting a stiffer behavior during isotropic compression, and mobilizing smaller shear strengths and effective friction angles. Triaxial testing also involves many sources of errors that could significantly affect shear strength parameters if not corrected. Extensive errors are investigated and it is found that negligence in making corrections accounting for these errors will result in an overestimation as much as 42% and 15 degrees in the critical shear strength and critical state friction angle, respectively. Furthermore, the measured critical state parameters and shear strengths are employed to compare the static and seismic slope stability of an earth embankment dam, calibrate a critical state soil constitutive model, study the soil behavior under shallow foundations, and evaluate liquefaction triggering and failure of retaining structures. The results show that all of these analyses are significantly affected by the strength parameters of the same soil determined from different specimen sizes. While using small size samples for determining shear strength parameters might result in un-conservative design, the choice of a large sample size is consequently a more accurate representation of soil strength conditions and field deformations.
Omar, Tarek, "Specimen Size Effect on Shear Behavior of Loose Sand in Triaxial Testing" (2013). Electronic Thesis and Dissertation Repository. 1755.