Location

San Diego, California

Session Start Date

5-24-2010

Session End Date

5-29-2010

Abstract

Cyclic threshold shear strain, γt, is small cyclic shear strain amplitude above which soil properties significantly change with the number of cycles, N, and below which such changes are for all practical purposes negligible. To date, three cyclic threshold shear strains have been experimentally verified: for cyclic settlement (cyclic compression), for residual cyclic pore water pressure, and for cyclic stiffening. Subject of the paper is testing of fourth cyclic threshold shear strain for cyclic degradation, γtd. When fully saturated soil is subjected in undrained conditions to moderate or large cyclic strain-controlled loading, its secant shear modulus, Gs, decreases with N. This is quantified for given cyclic shear strain amplitude, γc, by degradation index, δ = GsN /Gs1, where GsN = Gs at cycle N. Index δ and N are related via degradation parameter t = −(logδ / logN) which measures the rate of cyclic degradation. At γc < γtd there is no cyclic degradation and t = 0. If γc > γtd cyclic degradation takes place and t > 0. With a special simple shear device for small-strain testing the variation of t with γc was examined and γtd evaluated for three clayey soils. Results show that γtd increases with plasticity index, PI. For PI=12 γtd=0.015%, for PI=26 γtd=0.04, and for PI=47 clay γtd=0.05%. Testing procedure and comparison to other types of γt are presented.

Department(s)

Civil, Architectural and Environmental Engineering

Appears In

International Conferences on Recent Advances in Geotechnical Earthquake Engineering and Soil Dynamics

Meeting Name

Fifth Conference

Publisher

Missouri University of Science and Technology

Publication Date

5-24-2010

Document Version

Final Version

Rights

© 2010 Missouri University of Science and Technology, All rights reserved.

Document Type

Article - Conference proceedings

File Type

text

Language

English

Share

COinS
 
May 24th, 12:00 AM May 29th, 12:00 AM

Threshold Shear Strain for Cyclic Degradation of Three Clays

San Diego, California

Cyclic threshold shear strain, γt, is small cyclic shear strain amplitude above which soil properties significantly change with the number of cycles, N, and below which such changes are for all practical purposes negligible. To date, three cyclic threshold shear strains have been experimentally verified: for cyclic settlement (cyclic compression), for residual cyclic pore water pressure, and for cyclic stiffening. Subject of the paper is testing of fourth cyclic threshold shear strain for cyclic degradation, γtd. When fully saturated soil is subjected in undrained conditions to moderate or large cyclic strain-controlled loading, its secant shear modulus, Gs, decreases with N. This is quantified for given cyclic shear strain amplitude, γc, by degradation index, δ = GsN /Gs1, where GsN = Gs at cycle N. Index δ and N are related via degradation parameter t = −(logδ / logN) which measures the rate of cyclic degradation. At γc < γtd there is no cyclic degradation and t = 0. If γc > γtd cyclic degradation takes place and t > 0. With a special simple shear device for small-strain testing the variation of t with γc was examined and γtd evaluated for three clayey soils. Results show that γtd increases with plasticity index, PI. For PI=12 γtd=0.015%, for PI=26 γtd=0.04, and for PI=47 clay γtd=0.05%. Testing procedure and comparison to other types of γt are presented.