CASE HISTORY-BASED LIQUEFACTION EVALUATION OF MULTI-LAYERED SITES WITH FINES-DOMINATED MATERIALS

Author

• Pourya Kargar, Southern Illinois University CarbondaleFollow

Date of Award

5-1-2026

Degree Name

Doctor of Philosophy

Department

Engineering Science

First Advisor

Osouli, Abdolreza

Abstract

Fines-dominated soils are materials that are composed of at least 20% fines. The liquefaction response of fines-dominated soils would be typically assessed using empirical and semiempirical methods, even though most of these methods were originally developed to address sand-like materials. In these methods, the results of in situ tests (CPT, SPT, or shear wave velocity) or the undrained shear strength parameter are commonly used to calculate the cyclic resistance ratio (CRR) of the soil, which then is compared to earthquake-induced cyclic stress ratio (CSR) at the site. Although the empirical and semiempirical procedures are valuable tools for liquefaction evaluation, there are serious limitations with these methods especially in their application for the sites with fines-dominated materials. For example, the use of observations made in case histories involving fines-dominated materials by these methods is very limited or these procedures cannot capture the existing interaction effects in a multilayer system (multi-layer effects) during the earthquake. To overcome the limitations of these procedures, calibrated and validated numerical modeling procedures may be used. Recent advancements in constitutive models allow nonlinear numerical modeling of excess porewater pressure (EPWP) build up due to seismic events in various geotechnical mediums and seismic conditions. These advanced constitutive models alongside well-documented case histories could be used for assessing the complicated liquefaction behavior of sites with fines-dominated materials. This dissertation aims at a case history-based investigation to evaluate the liquefaction and overall seismic responses of sites with fines-dominated materials by accounting for system response effects. This dissertation focuses on the changes in the liquefaction behavior and overall seismic response of such sites due to the existence and interaction of liquefiable and non-liquefiable soil layers in the site profile, multi-layer effects. To reach this objective, this dissertation develops a nonlinear dynamic analysis procedure based on advanced constitutive models that are incorporated into a finite difference fully coupled modeling platform. Then this dissertation verifies the performance of the proposed procedure using the downhole array case histories in which liquefaction/non-liquefaction data of fines-dominated materials are recorded. To shed light on how the presence of liquefiable and non-liquefiable interlayers might affect the characteristics of liquefaction and seismic responses of the site, the triggering and manifestation features of liquefaction, as well as resulting surface motions, were assessed for two different cases. First, when a liquefiable interlayer is in a profile that might be liquefaction susceptible or not (i.e., the silty sand material of the WLA site for the susceptible profile and silty clay materials of WLA site as the liquefaction non-susceptible profile materials), and second, a non-liquefiable interlayer in a profile mainly composed of liquefaction susceptible materials (i.e., the silty sand materials of WLA site). It was shown that in many of the investigated cases, the response of the sites does not support the concepts proposed by simplified liquefaction assessment methods which are commonly used in practice. In addition, several multi-layer effects including asynchronous liquefaction that can substantially change the liquefaction response of susceptible sites, and was identified for the first time herein, were delineated further using the conducted liquefaction analyses on the synthetic profiles.