Date of Award

Fall 2023

Document Type

Open Access Thesis

Department

Civil and Environmental Engineering

First Advisor

Inthuorn Sasanakul

Abstract

Throughout history in the field of geotechnical earthquake engineering, there have been numerous experimental investigations on the dynamic behavior of soils. Many of these efforts have been focused on sand and silty sand material due to their susceptibility to liquefaction phenomena. However, gravelly soil material (i.e., soil in which gradation contains primarily gravel and sand) has exhibited this phenomenon in response to earthquake loading in many case histories. Therefore, it is important to extend the experimental assessment of gravelly soil material to develop a better understanding of the cyclic response and to support the development of numerical models. This study evaluates the impact of drainage conditions on the dynamic response of gravelly soils through a series of undrained and drained load-controlled cyclic triaxial element tests and centrifuge physical modeling tests. The material was saturated mine waste rock classified as gravelly soil composed of gravel, sand, and fines and was tested in loose to very dense conditions. Undrained and drained triaxial element tests aimed to evaluate liquefaction characteristics and develop an empirical model for excess pore water pressure and cyclic-induced volumetric strain. The effect of sample size of cyclic triaxial drained test was investigated for 6- and 4-inch diameter samples. The results of volumetric strain between the two sample sizes were observed to agree well. This provides an opportunity to further research on gravelly soils without the requirement of large-scale triaxial devices. Axial strain was used to correlate pore water pressure and volumetric strain from the undrained and drained triaxial tests, respectively. The correlated relationship suggests that to obtain the same amount of volumetric strain, there must be greater pore pressure generation in dense soil. This correlation developed by ideal drainage conditions in element tests was compared to the partial drainage condition in centrifuge models. Two centrifuge models in dense and loose condition aimed to simulate an approximately 6 m soil profile with a vertical effective stress of 140 kPa located at the middle of the model. Settlement measurements were analyzed in the upper and lower half of the soil model. Greater settlement was observed in the upper half of both models. In contrast, maximum excess pore pressure manifested in the lower half of the models. Shear modulus and damping were reported for both density conditions. In general, both models had a reduction in shear modulus in the initial loading cycles followed by an increasing trend for the remainder of shaking. At the end of shaking, the loose model ultimately gained stiffness. Damping decreased with increasing loading cycle for both density conditions. The impacts of different drainage conditions for the two laboratory methods were discussed. Triaxial tests resulted in conservative values of excess pore water pressure due to the undrained condition. Partial drainage in centrifuge models resulted in larger volumetric strains at lower values of Ru in comparison to triaxial element tests. Findings from this study indicate that greater volumetric strain or settlement can be expected at lower Ru under field conditions than predicted by triaxial testing.

Rights

© 2024, Pressley Margaret Perry

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