Drained cyclic preshearing effects on the liquefaction resistance of sands

Sibley, Erin Leigh Dillon

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Description

Title

Drained cyclic preshearing effects on the liquefaction resistance of sands

Author(s)

Sibley, Erin Leigh Dillon

Issue Date

2016-11-23

Director of Research (if dissertation) or Advisor (if thesis)

• Olson, Scott M.
• Polito, Carmine P

Doctoral Committee Chair(s)

Olson, Scott M.

Committee Member(s)

• Mesri, Gholamreza
• Tutumluer, Erol
• Rutherford, Cassandra J.

Department of Study

Civil & Environmental Eng

Discipline

Civil Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Liquefaction
• Preshearing
• Sand
• Cyclic Simple Shear

Abstract

Liquefaction-induced ground failures are a major source of damage and economic loss from earthquakes. Because of this, considerable research has been conducted to investigate factors that affect the liquefaction resistance of coarse-grained soils. Among these, shearing history has been shown to either decrease or increase liquefaction resistance. This past shearing – known as “preshearing” – is defined as the process of minor grain adjustments into a more stable configuration under external shear stress, which can be either transient or sustained, and either cyclic or monotonic. Specifically, undrained preshearing related to earthquakes motivated early preshearing studies and has been the predominant focus of subsequent preshearing research. In contrast, few studies have evaluated drained preshearing, which is a viable source of liquefaction improvement in the field. Moreover, a review of preshearing literature reveals that existing methods of defining preshearing are problematic, as they fail to accurately characterize the wide variety of loading mechanisms and drainage conditions which preshearing encompasses. Finally, few studies have addressed specific field sources of preshearing to determine practical guidelines or methods for integrating preshearing effects into traditional liquefaction triggering analysis in a way that is meaningful for practitioners. With this background in mind, this study seeks to bridge the gaps in knowledge that exist regarding preshearing leading to improved liquefaction resistance. A systematic laboratory testing program was undertaken to provide a more comprehensive understanding of drained cyclic preshearing – both the factors that influence it as well as its effect on liquefaction resistance. The study consisted of over 300 cyclic simple shear tests performed on reconstituted specimens of four sands prepared to varying densities. Small-amplitude drained cyclic preshearing strains of 0.02-0.3% were applied to the specimens for 10-1000 cycles. After drained preshearing, the specimens were subjected to higher amplitude cyclic shear strains under constant-volume conditions until liquefaction occurred. When compared with constant-volume cyclic shear tests without preshearing, the results provided key insights into important preshearing parameters (amplitude and duration) and their effect on relative density and cyclic shearing resistance of the soil. Within the context of these findings, a preshearing framework is proposed that relates preshearing to the cyclic (liquefaction) resistance curve. This framework quantifies how a soil is influenced by different preshearing intensities, regardless of test method or drainage conditions. In addition, the results from the laboratory testing program were used to evaluate the effectiveness of the energy-based GMP model for predicting porewater pressure generation in presheared soils and to examine how the concept of dissipated energy can be applied to cyclic simple shear tests on presheared sands to characterize the combined effects that amplitude and duration of preshearing have on subsequent constant-volume shearing behavior. This approach provides several advantages for not only for quantifying both preshearing and its resulting impact it has liquefaction resistance and porewater pressure generation, but also for integrating preshearing into future energy-based field liquefaction correlations. Finally, the results from the preshearing tests were incorporated into the field-based liquefaction boundary curves used in conventional liquefaction triggering analysis. These preshearing-integrated boundary curves are used to demonstrate how preshearing effects can be integrated into liquefaction triggering analysis. Likewise, various field source of preshearing are discussed, highlighting the importance of understanding and better quantifying field sources of preshearing for more accurate liquefaction assessment. Finally, recommendations are made for future research and for implementing the findings of this study into engineering practice.

Graduation Semester

2016-12

Type of Resource

text

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Copyright and License Information

Copyright 2016 Erin Leigh Dillon Sibley

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