Laboratory Investigations of Cohesionless Shear Strength in Low Confinement Environments
Winters, Katherine E.; Taylor, Oliver-Denzil S.; Berry, Woodman W.; Cunningham, Amy L.; Rowland, Wesley R.; Antwine, Mark D.
In low-confining stress environments, Mohr-Coulomb failure mechanics implies that a cohesionless soil has negligible shear strength. This report presents results of total stress laboratory investigations from triaxial and simple shear loadings for three loose- to medium dense, cohesionless materials, i.e., a poorly-graded sand (SP), a silty sand (SM), and a silt (ML), at confining pressures ranging from zero to 1000 kPa, as well as cyclic ring shear testing of the SP material at confining pressures from 10 to 100 kPa. All materials exhibited shear strengths and stress paths in excess of expected failure surfaces at confining pressures under 100 kPa. The data indicate that cohesionless soils exhibit significant soil fabric strength characteristics that are not captured by the standard internal friction angle definition, as evidenced by the shear stress intercept of the trendlines relating shear strength and confining pressure. Under low confinement, the continuum fabric dominates the angle of the Mohr envelope. The significant difference in the Mohr envelope shape illustrates that the internal fabric’s ability to resist different loading mechanisms cannot be assumed by a linear approximation.
Geotechnical and Structures Laboratory (U.S)
Laboratory testing; Low confinement; Soil fabric; Soil mechanics; Shear strength; Shear strength of soils-Testing; Sandy soils; Soil erosion; Soil mechanics
Technical Report (Geotechnical and Structures Laboratory (U.S));no.ERDC/GSL TR-18-22
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