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    Interpretation of Triaxial Test Results of Cohesionless Soils: A New Model

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    The demand for more reliable methods of predicting the stress-strain relationship of large particle soils, and for more realistic assessment of the influence of grain characteristics on the shear behavior of cohesionless materials, makes it very important that the geotechnical profession develop a reliable modeling technique to accurately evaluate the effects of test and specimen variables. Large size particles in a soil matrix make it difficult to determine the strength parameters using conventional laboratory equipment. The relevant properties of the prototype materials (which contain large size particles) could be evaluated by using laboratory-reconstructed specimens with smaller particle sizes.

    Traditionally, shear strengths of different types of cohesionless soils were compared using a constant relative density or void ratio. It was found that because of the differences in the range of limiting densities, soils with a constant relative density or void ratio but with different grain sizes would undergo different behavior during shear. At a constant void ratio or a constant relative density, some soils may experience volume increase; others may undergo a volume decrease; still others may experience no volume change during shear. Thus, comparing the shear strengths of different types of soils (that is, different grain size materials) based on the soils' relative densities or void ratios may led to inaccurate conclusions. The model should be based instead on the soils' response under the applied loads rather than their states of compaction.

    This paper presents a new model (percent dilatation) whereby the shear strength of cohesionless soils, comprised of different particle sizes, can be compared and studied based on their behaviors during shear. The percent dilatation (PD) model was developed using data from 178 drained static triaxial tests, designed and conducted to study the effects of soil density, confining pressure, moisture content, and grain characteristics (size, gradation, shape, and particle angularity) on the shear strength of cohesionless soils.


    cohesionless, sand, gravel, triaxial, shear strength, ultimate strength, grain size

    Author Information:

    Baladi, GY
    Associate professor of civil engineering, Michigan State University, East Lansing, MI

    Wu, TTH
    Engineer, Jones, Kwong, Kishi Consulting Engineers, West Vancouver, British Columbia

    Committee/Subcommittee: D18.05

    DOI: 10.1520/STP29099S