LEE- Deprem Mühendisliği Lisansüstü Programı
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Yazar "Bayat Eseller, Esra" ile LEE- Deprem Mühendisliği Lisansüstü Programı'a göz atma
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ÖgeDynamic response of partially saturated sands under foundations(Graduate School, 2021-09-09) Viand Seyedi, Seyed Mohsen ; Bayat Eseller, Esra ; 802142003 ; Earthquake EngineeringThe liquefaction or softening of the foundation soils and the potential vulnerability of existing buildings on liquefiable soils continues to be of major concern to the public because it has repeatedly caused severe damages to buildings with shallow or heavy foundations during earthquakes, such as 1967 Niigata (Japan), 1999 Adapazari (Turkey), 2010 Maule (Chile) and the 2011 Christchurch (New Zealand) earthquakes. The liquefaction of soils leads to a decrease in the effective stress and a consequent degradation in the associated shear strength and stiffness. When the excess pore pressures are built up to initiate full liquefaction (near-zero effective stress state) beneath the foundations, significant deformations such as excessive settlements, tilting and shifting of overlying buildings can occur. An urgent need exists to develop costeffective liquefaction mitigation measures that can be easily and widely used for buildings founded on a liquefiable soil. In recent years, some researchers have been investigating liquefaction mitigation techniques, through series of laboratory tests that involve the artificial introduction of air/gas bubbles and creating partially saturated zones in the liquefiable soil deposits. These techniques intend to prevent the occurrence of liquefaction by increasing the compressibility of the pore fluid with the generation of some amount of air/gas in the fully saturated sand, thus basically, by transforming the sand into partially saturated state. Also, some physical model tests have been conducted to study the liquefaction behavior of partially saturated soils in free field and under foundations. The research, particularly investigating the response of shallow foundations rested on these soils, has suggested that the liquefaction potential of liquefiable soils and relevant building settlements significantly decrease by the reduction of degree of saturation. Although there are many studies in the literature for liquefaction response analysis of fully or partially saturated sands and building movements resting on these sands, performance-based earthquake engineering requires improved procedures to give a deep and more realistic insight into the field. This thesis includes the initial research tasks of a TÜBİTAK funded project (No: 213M367) titled ''Dynamic Response of Sands Mitigated by IPS (Induced Partial Saturation) under New and Existing Structures''. The primary goal of this thesis is numerically modelling of partially saturated sands in free field and under foundations and to determine how much partial saturation should be induced in liquefiable areas. It uses a novel technique to reduce degree of saturation of fully saturated sands that is called Induced Partial Saturation, IPS. This thesis also will indicate how accurate the RuPSS (a novel model to predict excess pore water pressure ratio in partially saturated sands) empirical model is in predicting the liquefaction response of remediated sites by IPS. In this due, the application of IPS technique in tackling the liquefaction damages in free field and under foundations will be examined and modelled in this thesis. The main goals of this thesis can be listed as below: 1) An exhaustive literature review was done to collect almost all of the studies that involve reduction in the degree of saturation and creation of partially saturated zones in the liquefiable soil deposits. 2) A hypothesis has been made in the proposal of the thesis regarding the excess pore pressure generation (during the shaking phase) and its dissipation (during the post shaking phase) along with the settlement of free field and foundations. Its accuracy will be evaluated in the thesis through the numerical models and validations with studies available in the literature. 3) Analysis of the behaviour of fully and partially saturated sands under cyclic loadings considering different soil parameters through numerical modelling and comparison of the numerical analysis results in FLAC3D software with the experimental data available in the literature. 4) Analysis of the behaviour of fully and partially saturated sands under earthquake records in free fields and under foundations considering different soil parameters through numerical modellings in FLAC3D software. 5) There is a key parameter required in numerically modelling the partially saturated sands that is called air-water mixture bulk modulus, Kaw. According to the literature review, there is a well known equation for predicting Kaw. It will be shown that this equation equation is not very accurate in predicting a proper value for Kaw for soils with degrees of saturation below 80% or for partially saturated sands mitigated by IPS against liquefaction. Proposing an alternative empirical function to predict Kaw of partially saturated sands for using in numerical modellings will be the fourth task. The proposed function will be examined through comparison of numerical analysis results with those obtained from experimental test results in the literature. 6) A parametric study on the liquefaction analysis of fully and partially saturated sands in free field and under foundations in PLAXIS2D software. Results were presented in terms of excess pore pressure generations and dissipations and also the settlement responses both in free field and under foundations. 7) Finally, according to the obtained results and comprehensive literature review performed in this thesis, it is was concluded that there are some gaps in the field of partial saturation application in both experimental and numerical studies. Those gaps were listed and discussed in detail to pave the way of finding topics of research for the future studies. The researchers and engineers will benefit by using the outcomes and proposed models of this thesis in their research or in real case projects to analyze the dynamic response of partially saturated sands naturally existing in nature. Also, the mathematical predictive models that will be developed in this thesis will not only be used in the implementation of IPS, but also in the estimation of liquefaction responses in partially saturated sands existing under buildings. Besides contributions in science and engineering, the ultimate goal of this thesis is to help the safety of our society. The best outcome of this thesis will be to provide opportunities for the IPS technique to be implemented in liquefiable areas selected in Turkey and determination of partial saturation needed to improve the liquefiable zones.