Location

Arlington, Virginia

Session Start Date

8-11-2008

Session End Date

8-16-2008

Abstract

In this paper, we examine the role of grain mineralogy and compressibility, sample preparation, and shear strain/displacement levels on the shearing behavior of sands using undrained triaxial and constant volume ring shear tests in an attempt to explain some discrepancies observed between field and laboratory behavior. As expected, preparation by moist tamping can produce specimens that are contractive throughout shear, while counterparts prepared using pluviation exhibit dilative behavior at intermediate shear strain/displacement levels (i.e., after initial yield). However, both triaxial and ring shear tests illustrate that some sands consisting of more compressible minerals can exhibit entirely contractive behavior regardless of the sample preparation method. These preliminary tests suggest that laboratory testing of pure quartz sands may result in potentially misleading conclusions regarding the field behavior of mixed mineral soils involved in many liquefaction flow failures and long run-out landslides. Furthermore, grain crushing at larger displacements (larger than those that can be achieved in the triaxial device) results in net contractive response regardless of the sample preparation method or the grain mineralogy. Grain crushing has been observed in shear zones formed during a few well-documented long run-out landslides. The combination of these factors: grain mineralogy and compressibility, particle damage and crushing, and shear zone formation may help to explain some discrepancies observed between field and laboratory behavior of sands.

Department(s)

Civil, Architectural and Environmental Engineering

Appears In

International Conference on Case Histories in Geotechnical Engineering

Meeting Name

Sixth Conference

Publisher

Missouri University of Science and Technology

Publication Date

8-11-2008

Document Version

Final Version

Rights

© 2008 Missouri University of Science and Technology, All rights reserved.

Document Type

Article - Conference proceedings

File Type

text

Language

English

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Aug 11th, 12:00 AM Aug 16th, 12:00 AM

The Importance of Mineralogy and Grain Compressibility in Understanding Field Behavior of Failures

Arlington, Virginia

In this paper, we examine the role of grain mineralogy and compressibility, sample preparation, and shear strain/displacement levels on the shearing behavior of sands using undrained triaxial and constant volume ring shear tests in an attempt to explain some discrepancies observed between field and laboratory behavior. As expected, preparation by moist tamping can produce specimens that are contractive throughout shear, while counterparts prepared using pluviation exhibit dilative behavior at intermediate shear strain/displacement levels (i.e., after initial yield). However, both triaxial and ring shear tests illustrate that some sands consisting of more compressible minerals can exhibit entirely contractive behavior regardless of the sample preparation method. These preliminary tests suggest that laboratory testing of pure quartz sands may result in potentially misleading conclusions regarding the field behavior of mixed mineral soils involved in many liquefaction flow failures and long run-out landslides. Furthermore, grain crushing at larger displacements (larger than those that can be achieved in the triaxial device) results in net contractive response regardless of the sample preparation method or the grain mineralogy. Grain crushing has been observed in shear zones formed during a few well-documented long run-out landslides. The combination of these factors: grain mineralogy and compressibility, particle damage and crushing, and shear zone formation may help to explain some discrepancies observed between field and laboratory behavior of sands.