Liquefaction potential and post-liquefaction settlement of saturated clean sands: and effect of geofiber reinforcement

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Author
Omarov, Maksat
Keyword
Soil liquefaction
Shear strength of soils
Reinforced soils
Earthquake engineering
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URI
http://hdl.handle.net/11122/12748
Abstract
"Liquefaction of saturated granular soils has been the cause of most geotechnical hazards during earthquakes. Development of excess pore pressures in saturated soils when subjected to cyclic loading has been shown to cause the liquefaction, which can be simply described as the transformation of stable soil structure into unstable liquid form. Majority of the previous laboratory studies have been focused on stress-controlled loading. However, the generation of excess pore pressure is better characterized by the induced shear strains. The objectives of this study were: (i) to investigate the liquefaction potential and post-loading volumetric strain of saturated clean sands through strain-controlled testing; and (ii) to study as an alternative mitigation technique, the influence of geofiber reinforcement on exess pore pressure generation and post-liquefaction settlement of saturated sands. Undrained, strain-controlled, cyclic triaxial tests were performed in the following categories: (1) tests performed under different effective consolidation stresses; (2) tests performed at various number of loading cycles; (3) tests performed at different relative densities; and (4) tests performed on geofiber-reinforced sand specimens. The liquefaction potential of specimens subjected to different levels of shear strains were investigated with respect to the developed excess pore pressures. Reduction in the volume of the specimens with the dissipation of generated excess pore water pressure was studied by allowing for drainage after cyclic loading. Additionally, the influence of geofibers as a possible mitigation measure against the excess pore pressure development and post-loading volumetric straining of clean sands was investigated. The results from this study were used to develop insight into the behavior of clean and geofiber-reinforced sands under seismic loading conditions. Based on the test results, geofiber-reinforced seismic loading conditions was found that the number of loading cycles has significant influence on the generation of excess pore pressure and post-loading volumetric strain. Specimens subjected to continued loading after initial liquefaction indicated about three times larger volumetric strains when compared to those allowed to drain after initial liquefaction. Soil specimens consolidated to 100kPa effective stress were found to experience less volumetric strain than that observed in specimens consolidated to 400kPa effective consolidation stress; however, the excess pore pressure generation at 100kPa effective stress was about two times larger than that measured at 400kPa effective stress. In general, geofiber-reinforced specimens showed less excess pore pressures when compared to clean sand specimens; while post-loading settlement were observed to be nearly two times larger for specimens with 1%geofiber content when compared to clean sand specimens"--Leaves iii-iv
Description
Thesis (M.S.) University of Alaska Fairbanks, 2010
Table of Contents
1. Introduction -- 1.1. Subject overview -- 1.2. Scope of the research -- 1.3. Organization of the thesis -- 2. Literature review -- 2.1. Introduction -- 2.2. Liquefaction of soils -- 2.3. Evaluation of liquefaction potential -- 2.3.1. Stress-based approach -- 2.3.2. Strain-based approach -- 2.4. Earthquake induced settlements of sands -- 2.4.1. Settlements of saturated sands -- 2.4.2. Estimating post cyclic loading settlements of sand deposits -- 2.5. An alternative liquefaction mitigation technique -- 2.5.1. Previous research on fiber reinforced sands -- 2.6. Summary -- 3. Methodology for cyclic strain-controlled tests -- 3.1. Introduction -- 3.2. Cyclic triaxial testing -- 3.2.1. Geotechnical consulting and testing systems (GCTC) cyclic triaxial equipment -- 3.2.2. Equipment verification -- 3.3. Materials used -- 3.3.1. Gradation -- 3.3.2. Specific gravity -- 3.3.3. Maximum and minimum dry densities -- 3.4. Sample preparation -- 3.4.1. Dry pluviation -- 3.4.2. Water sedimentation -- 3.4.3. Moist tamping (undercompaction) -- 3.4.4. Sample preparation for clean sand specimens -- 3.4.5. Sample preparation for geofiber mixed specimens -- 3.5. Testing stages -- 3.5.1. Saturation -- 3.5.2. Consolidation -- 3.5.3. Cyclic loading -- 3.5.4. Post testing recordings -- 3.6. Summary -- 4. Test results and findings -- 4.1. Introduction -- 4.2. Strain controlled tests with clean sands -- 4.2.1. Tests with different consolidation stresses -- 4.2.2. Tests with differential number of loading cycles -- 4.2.3. Tests with different relative densities -- 4.3. Settlement of saturated sands following cyclic loading -- 4.3.1. Influence of number of loading cycles -- 4.3.2. Volumetric strain after initial liquefaction -- 4.3.3. Influence of consolidation stree -- 4.4. Case study -- 4.5. Test results for geofiber reinforced specimens -- 4.5.1. Excess pore pressure generation of geofiber reinforced sands -- 4.5.2. Influence of geofibers on post loading volumetric strains -- 4.6. Summary -- 5. Conclusion -- 5.1. Summary -- 5.1.1. Results and findings in terms of pore pressure generation -- 5.1.2. Results and findings in terms of post loading reconsolidation volumetric strains -- 5.2. Practical implications of the results -- 5.3. Recommendations for future research -- References.
Date
2010-05
Type
Thesis
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