Case history-based analysis of liquefaction in sloping ground

Liquefaction;Liquefied Shear Strength;Yield Shear Strength;Liquefaction Triggering;Post Triggering;Liquefaction Susceptibility;Compressibility of soils

Muhammad, Kashif

关键词: Liquefaction;    Liquefied Shear Strength;    Yield Shear Strength;    Liquefaction Triggering;    Post Triggering;    Liquefaction Susceptibility;    Compressibility of soils;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/42461/Kashif_Muhammad.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Liquefaction is one of the most interesting and controversial phenomenon in geotechnical engineering. This phenomenon has caused numerous slope failures in saturated deposits of fine, loose sands and other cohesionless soils. Because of the catastrophic nature of the failures and their impact on the built environment, liquefaction problems have received a great deal of attention among the geotechnical community and many efforts have been made to clarify basic mechanisms and various aspects of the problems associated with liquefaction. Although liquefaction can occur in both level and sloping ground, this research focuses on sloping ground liquefaction. The analysis of liquefaction in sloping ground is divided into three steps: (1) liquefaction susceptibility; (2) liquefaction triggering; and (3) post-triggering stability analysis. Existing procedures to evaluate liquefaction susceptibility, triggering, and post-triggering stability in sloping ground include: (1) methods based on laboratory soil testing; (2) methods based on empirical relationships back-calculated from case histories; (3) finite element methods involving constitutive models of sandy soils; and (4) combination laboratory testing and back-analysis of case histories or laboratory testing and finite element modeling. This study investigates approach (2) because it does not require expensive and time-consuming laboratory testing, it is simple for engineers to apply in practice, and it do not require input parameters that are hard to determine and may have little or no physical meaning. Specifically in this study, the author documented and analyzed 31 reasonably well-documented case histories and combined those with 33 case histories analyzed by Olson (2001). Liquefaction susceptibility analysis evaluates whether a particular soil is susceptible to liquefaction, i.e., is the soil contractive or dilative during shear? The combined case history database was used to evaluate: (1) empirical and semi-empirical contractive-dilative boundaries; (2) the role of fines content on liquefaction susceptibility in sloping ground conditions; and (3) the viability of an extended cone penetration test “compressibility” correction factor for susceptibility analysis. If a soil deposit is susceptible to liquefaction, a liquefaction triggering analysis is performed. This step involves evaluating whether a particular combination of static and dynamic/seismic loads are sufficient to trigger liquefaction. The author used the combined case history database to evaluate: (1) available empirical and semi-empirical relationships for yield shear strength ratios, su(yield)/'vo; and (2) the effect of the mode of shear on yield shear strengths mobilized in flow failure case histories. If liquefaction is triggered in a soil deposit, a post-triggering stability (flow failure) analysis is performed. This step evaluates whether the geo-structure is stable when the shear resistance includes the liquefied shear strength, su(liq). The author used the combined case history database to evaluate: (1) available empirical and semi-empirical relationships for liquefied shear strength ratios, su(liq)/s'vo; (2) the effect of the mode of shear on yield shear strengths mobilized in flow failure case histories; and (3) the relation between brittleness index and su(liq). Finally, three case histories subjected to six separate earthquakes were used to evaluate the proposed liquefaction evaluation procedure. These cases were analyzed for susceptibility, triggering and post triggering to predict the field behavior, and illustrated that the proposed procedure is able to capture the severity of failure experienced at the individual sites during earthquake shaking.