Soil liquefaction during earthquakes is a phenomenon that can cause tremendous damage to structures such as bridges, roads, buildings, and pipelines. The objective of this research is to develop an energy-based approach for evaluating the potential for liquefaction triggering. The current state-of-practice for the evaluation of liquefaction triggering is the "simplified" stressbased framework where resistance to liquefaction is correlated to an in situ test metric (e.g., normalized standard penetration test N-value, N1,60cs, normalized cone penetration tip resistance, qc1Ncs, or normalized small strain shear wave velocity, Vs1). Although rarely used in practice, the strain-based procedure is commonly cited as an attractive alternative to the stress-based framework because excess pore pressure generation (and, in turn, liquefaction triggering) is more directly related to strains than stresses. However, the method has some inherent and potentially fatal limitations in not being able to appropriately define both the amplitude and duration of the induced loading in a total stress framework. The energy-based method proposed herein builds on the merits of both the stress- and strain-based procedures, while circumventing their inherent limitations. The basis of the proposed energy-based approach is a macro-level, low cycle fatigue theory in which dissipated energy (or work) per unit volume is used as the damage metric. Because dissipated energy is defined by both stress and strain, this energy-based method brings together stress- and strain-based concepts. To develop this approach, a database of liquefaction and nonliquefaction case histories was assembled for multiple in situ test metrics. Dissipated energy per unit volume associated with each case history was estimated and a family of limit-state curves were developed using maximum likelihood regression for different in situ test metrics defining the amount of dissipated energy required to trigger liquefaction. To ensure consistency between these limit-state curves and laboratory data, a series of cyclic tests were performed on samples of sand. These laboratory-based limit-state curves were reconciled with the field-based limit-state curves using a consistent definition of liquefaction. / Doctor of Philosophy / Soil liquefaction during earthquakes is a phenomenon that can cause tremendous damage to structures such as bridges, roads, buildings, and pipelines. The objective of this research is to develop an energy-based approach for evaluating the potential for liquefaction triggering. Current procedures to evaluate liquefaction triggering include stress-based and strain-based procedures. However, these procedures have some inherent and potentially fatal limitations. The energy-based method proposed herein builds on the merits of both the stress- and strain-based procedures, while circumventing their inherent limitations. The proposed energy-based approach uses dissipated energy (or work) per unit volume to evaluate the potential for liquefaction. Because dissipated energy is defined by both stress and strain, this energy-based method brings together stress- and strain-based concepts. To develop this approach, a database of case histories in which liquefaction was either observed or not observed was assembled. Dissipated energy per unit volume associated with each case history was estimated and a family of relationships was regressed to define the amount of dissipated energy required to trigger liquefaction. Results from a series of cyclic laboratory tests performed on samples of sand were reconciled with the field-based relationships using a consistent definition of liquefaction. This research proposes a method that is based on a robust mechanistic framework that will make it easier to evaluate liquefaction for circumstances that are not well represented in current liquefaction evaluation procedures. The components of the proposed energy-based procedure are developed consistently and are presented in such a way that this procedure can be readily adopted by practitioners who are already familiar with existing liquefaction evaluation procedures. The broader impacts of this work will help to minimize losses from earthquakes by improving the way engineers evaluate liquefaction.

Among the hard-hit cities during 17 August 1999 Kocaeli Earthquake (Mw 7.4), Adapazari is known for the prominent role of site conditions in damage distribution. Since the strong ground motion during the event was recorded only on a rock site, it is necessary to estimate the response of alluvium basin before any study on the relationship between the damage and the parameters of ground motion. Therefore, a series of site and laboratory tests were done on Adapazari soils in order to decrease the uncertainty in estimation of their dynamic properties. In downtown Adapazari, a 118 m deep borehole was opened in the vicinity of heavily damaged buildings for sample recovery and in-situ testing. The stiffness of the soils in-situ is first investigated by standard penetration tests (SPT) and by velocity measurements with P-S suspension logging technique. Disturbed samples were recovered by core-barrel and split-barrel samplers. 18 Thin-Walled tubes were successively used for recovering undisturbed samples. A series of monotonic and cyclic direct simple shear tests were done on specimens recovered from the Thin-Walled tubes. It is concluded that the secant shear modulus and damping ratio of soils exposed to severe shaking during the 1999 event are significantly smaller than those estimated by using the empirical relationships in literature. It is also observed that the reversed-S shaped hysteresis loops are typical for cyclic response of the samples.