Dissertation/Thesis Abstract

Evaluation of Seismic Behavior of Intermediate and Fine-Grained Soils
by Dahl, Karina Ruth, Ph.D., University of California, Davis, 2011, 1119; 3499425
Abstract (Summary)

Intermediate soils such as low plasticity silty clays, sandy clays, and clayey sands may exhibit characteristics from sand-like to clay-like, which make it difficult to determine the most appropriate engineering procedure for estimating their cyclic strengths. Cyclic strengths of sands are primarily estimated using liquefaction correlations to in-situ tests based on case-histories of observed ground failure and no ground failure. These correlations to in-situ penetration resistance and shear wave velocity were developed knowing conventional tube sampling caused excessive disturbance in cohesionless soils and unreliable laboratory test results. Cyclic strengths of clays on the other hand may be measured directly in the laboratory or estimated from empirical correlations to undrained strength. High-quality tube sampling in cohesive soils occurs primarily under undrained conditions with only small changes in void ratio to render relatively undisturbed specimens for laboratory testing. For intermediate soils, the fundamental behavior and the effects of sampling disturbance on laboratory test results are poorly understood, such that it can be difficult to determine whether the in-situ cyclic strengths would be better estimated using in-situ test-based correlations or laboratory testing of field samples.

The cyclic behavior and engineering procedures for evaluating the cyclic behavior of intermediate and fine-grained soils were evaluated in this thesis. Data on the cyclic behavior of these types of soils were compiled from the literature and used to examine lessons regarding different behaviors and procedures for evaluating monotonic and cyclic undrained strengths. Detailed laboratory testing studies were then performed for three different intermediate or fine-grained soils, and the results examined in conjunction with the complementary in-situ test data and associated site characterization data. Characterization of the three intermediate soils, which differed in fines content, plasticity index, and consolidation state, consisted of consolidation tests, monotonic, cyclic, and post-cyclic monotonic direct simple shear tests, and post-cyclic reconsolidation tests. Cyclic strengths determined from site-specific laboratory testing and from empirical correlations derived primarily for clays (e.g., the cyclic softening procedures of Boulanger and Idriss 2006, 2007), or primarily for sands (e.g., SPT- and CPT-based liquefaction correlations) were compared and the differences discussed. A new testing procedure to investigate a soils' susceptibility to disturbance during the extrusion, trimming, and mounting process was developed and applied to these three intermediate and fine-grained soils. The dataset compiled from these studies and the literature was then used to evaluate any characteristic trends in monotonic and cyclic behavior with fines content, plasticity index, consolidation state, or other indices. Lastly, guidance was provided regarding the planning and performing of laboratory testing programs for evaluating the in-situ cyclic strengths of intermediate and fine-grained soils. Updated correlations for cyclic strengths for fine-grained soils are then provided where experimental data exists.

Indexing (document details)
Advisor: Boulanger, Ross W.
Commitee: DeJong, Jason T., Kutter, Bruce L.
School: University of California, Davis
Department: Civil and Environmental Engineering
School Location: United States -- California
Source: DAI-B 73/07(E), Dissertation Abstracts International
Subjects: Geotechnology, Civil engineering
Keywords: Clay, Fine-grained soils, Intermediate soils, Seismic behavior, Silt, Strengths
Publication Number: 3499425
ISBN: 978-1-267-23853-5
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