Date of Award
8-16-2024
Document Type
Open Access Dissertation
Department
Civil and Environmental Engineering
First Advisor
Inthuorn Sasanakul
Abstract
Dynamic behavior of gravelly soil has gained more attention in recent years as several case histories of liquefaction of gravelly soil have been reported. Liquefaction can cause failure of infrastructure, leading to economic damage and loss of life. Gravelly soil has unique characteristics and engineering benefits, providing a prevalent and versatile construction material for various infrastructure projects. Therefore, understanding of the gravelly soil behavior under seismic load is critical for assessing the resilience of infrastructure located in seismically active regions. To date, only a few experimental research studies have focused on the dynamic response of gravelly soil, and these studies are mainly based on results obtained from conducting cyclic element tests (e.g., cyclic triaxial and cyclic simple shear tests). These element tests are limited in scale, and the results are insufficient for realistic field condition. As a result of the unavailability of data and given the importance of filling the knowledge gap, the objective of this research is to evaluate dynamic behavior of gravelly soils utilizing centrifuge modeling tests replicating complexities and more realistic field stress conditions.
The advanced laboratory tests were conducted on loose gravel-sand mixtures in this study. There are six mixtures: 20-80, 40-60, 50-50, 65-35, 80-20, and 100-00. The first number indicates the percentage of gravel, whereas the second number indicates the percentage of sand. Due to the influence of the composition, these specimens show differences in void ratio and permeability. Using the change of void ratio with percent gravel and inter-grain concept, the mixtures were grouped by their dominant behaviors (i.e., sand-like, gravel-like, or transition soil). The resonant column and bender element tests were utilized to characterize low-strain dynamic properties. A series of centrifuge tests were conducted to investigate the impact of soil composition on the progressive response across a wide range of shear strains. A series of centrifuge tests were conducted at 50-g centrifuge gravitational acceleration. Each centrifuge model was subjected to incrementally increasing shaking amplitudes from 0.01 g to 0.40 g with various numbers of cycles. During the entire duration of the test, acceleration time histories, the development of excess pore water pressure, and settlement were monitored. The acceleration time histories were subsequently utilized to calculate shear stress and shear strain at a particular depth of the model. The cyclic shear strain generated from these shaking events ranged from 0.006 to 3.8% in all models. The values of volumetric threshold shear strain in gravelly soil were evaluated from the generation of pore water pressure and volume change during shaking. The values were found to be in a range of 0.03 to 0.06% and are influenced by soil composition. The threshold strain increases as the amount of gravel in the soil mixture increases. The development of excess pore water pressure in gravel-like soils exhibits transient behavior, while residual excess pore water pressure was observed in sand-like soils. The accumulation of pore pressure leads to upward flow in sand-like soils while transient pore pressure behavior leads to oscillatory flow in gravel-like soils. Differences in stress-strain response and effects of the number of shaking cycles were observed in different soil mixtures depending upon the level of excess pore pressure. At low shaking amplitude and low excess pore pressure, stiffness degradation was observed while the stress-strain loop was symmetric. At high shaking amplitude and high excess pore pressure, significant stiffness degradation was observed followed by shear-induced dilation resulting in an asymmetrical stress-strain loop. This study clarifies the differences in the dynamic responses and behaviors of sand-like, gravel-like, and transition soil over a wide range of strains.
Rights
© 2024, Siwadol Dejphumee
Recommended Citation
Dejphumee, S.(2024). Dynamic Response Evaluation of Loose Gravelly Soils in Centrifuge Modeling Experiments. (Doctoral dissertation). Retrieved from https://scholarcommons.sc.edu/etd/7694