State of the Art: Laboratory Strength Testing of Soils

Saada, Adel S.; Townsend, Frank C.

doi:10.1520/stp28744s

Cited by 131 publications

(49 citation statements)

References 57 publications

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“…When the shear box apparatus does not correctly simulate the actual field conditions under which the soil deforms, doubt is cast upon the reliability of test results to be used in practical engineering designs. Besides the specimen scale effects, other testing-related issues of the DSA include non-uniform stress and strain, and the associated progressive failure inside the specimen (Terzaghi & Peck, 1948;Hvorslev, 1960;Saada & Townsend, 1981). In addition, ambiguities exist in interpreting shear strength parameters owing to the fact that principal stress rotation occurs continuously until the peak state, and the failure plane may deviate from the horizontal mid-plane (Morgenstern & Tchalenko, 1967;Jewell & Wroth, 1987).…”

Section: Introductionmentioning

confidence: 99%

Discrete element simulations of direct shear specimen scale effects

Wang¹,

Gutierrez²

2010

Géotechnique

111

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This paper presents a study of the micromechanics of granular materials as affected by the direct shear test scale using the discrete element method (DEM). Parametric studies were conducted to investigate the effects of specimen length and height scales (in relation to the particle size) on the bulk material shear strength and shear banding behaviour in the direct shear test. A mesh-free strain calculation method previously developed by the authors was used to capture and visualise the evolution of strain localisation inside the direct shear box. Simulation results show that the maximum shear strength measured at the model boundaries increases with decreasing specimen length scale and increasing specimen height scale. Micromechanics-based analysis indicates that the local and global aspects of fabric change and failure are the major mechanisms responsible for the specimen scale effect. Global failure along the primary shear band prevails when the specimen length scale and length to height aspect ratio are small, while progressive failure becomes more likely when the specimen length scale and aspect ratio become larger. Further quantifications of the specimen scale effects on the macroscopic behaviour of granular materials rely on the fundamental understanding of quantitative relationships between material fabric, anisotropy and bulk strength.

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Section: Introductionmentioning

confidence: 99%

Discrete element simulations of direct shear specimen scale effects

Wang¹,

Gutierrez²

2010

Géotechnique

111

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“…The test specimen, which represents a single point under consideration in the ground, must be subject to a reasonably uniform state of effective stress for accurate interpretations of the experimental data. However, in common with other devices for the shear strength measurement, the HCTA has been criticized (for example Saada and Townsend 1981) on account of the level of stress nonuniformity that may develop. A new HCTA that facilitates stress path testing over a wide strain range has been developed recently by O'Kelly and Naughton (2003,2005) at University College Dublin (UCD) and, in a general context; the study of the stress nonuniformity associated with this apparatus is an important consideration.…”

Section: Introductionmentioning

confidence: 99%

Stress non-uniformity in a hollow cylinder torsional sand specimen

Naughton

O’Kelly

2007

Geomechanics and Geoengineering

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Abstract. The hollow cylinder torsional apparatus (HCTA) facilitates more generalized stress path testing although it has been criticized on account of the level of stress nonuniformity that may develop due to the curvature of the test specimen walls. The stress nonuniformity that may develop in dense sand specimens (35.5-mm inner radius, 50.0-mm outer radius and 200-mm in height) over small-to-medium strain levels in the HCTA were studied using an isotropic linear-elastic stress analysis. The stress nonuniformity, quantified in terms of the stress nonuniformity coefficient R , increased in proportion to the stress ratio R, and was generally acceptable throughout the stress space for R 1.5. Regions where unacceptable stress nonuniformity may develop were identified in the vicinity of (b, ) = ( o . Placing restrictions on the difference in the confining pressures that may be applied across the specimen wall thickness was found to reduce the stress nonuniformity but also limited the regions in stress space that could be probed.

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“…To justify this assumption, Lucks et al (1972) performed theoretical linear elastic analyses of the NGI type DSST, showing that 70z of the sample was uniformly stressed. However Saada and Townsend (1981) criticised some of the assumptions used in such analyses, particularly concerning the amount ofˆxity at the boundaries, and cite the results of Wright et al (1978) who used photo-elastic methods to illustrate a nonuniform specimen stress distribution. Nevertheless, results from tests conducted by Vucetic and Lacasse (1982) in the NGI apparatus on medium stiŠ clay at diŠerent height to diameter ratios have shown that the non-uniformities do not signiˆcantly aŠect the measured soil behaviour.…”

Section: Direct Simple Shear Test (Dsst)mentioning

confidence: 99%

“…The primary criticisms applied to the direct shear test relate to the non-uniformity of stress and strain throughout the sample (Saada and Townsend, 1981). This occurs as a result of the rigid platens which are used to conˆne the specimen.…”

Section: Direct Shear Test (Dst)mentioning

confidence: 99%