Tensile Strength Characteristics of Unsaturated Sands
Publication: Journal of Geotechnical and Geoenvironmental Engineering
Volume 133, Issue 2
Abstract
Tensile strength characteristics of unsaturated sands are examined through a combined theoretical and experimental study. The characteristics of tensile strength in all three water retention regimes of pendular, funicular, and capillary are examined. A simple direct tensile strength apparatus is employed to determine tensile strength for sands with a broad range of particle sizes from silty sand to fine sand and medium sand over a full range of degree of saturation. Tensile strength characteristic curves (TSCC) are established experimentally for these sands and are used to validate the existing theories for tensile strength in the pendular regime. The TSCC for sand characteristically exhibits two zeros at 0 and near 100% saturation, and two peak values occurring in the pendular and capillary regimes, respectively. A minimum tensile strength is observed in the dense fine sand, indicating that either water bridges or pore pressure contributes exclusively to the tensile strength in the funicular regime of this sand. The maximum tensile strength for the silty sand is , the fine sand is , and the medium sand is . Comparison between the soil–water characteristic curves obtained for these sands indicates that the peak tensile strength in the capillary regime is highly correlated to the air-entry pressure. Photographs of the failure surfaces clearly delineate distinct geometric characteristics for different water retention regimes. Analysis of the patterns of failure surfaces in different water retention regimes indicates that the effective stress principle is valid for tensile stress failure in unsaturated sands.
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Acknowledgments
The writers wish to thank Stein Sture for the stimulating discussions on tensile strength of unsaturated sand, William J. Likos for providing thoughtful and critical comments on the manuscript, and Alexandra Wayllace for conducting the SWCCs of the sands. The funding for this research provided by Petroleum Research Fund of American Chemical Society (Grant No. UNSPECIFIED42688-AC9) is greatly appreciated.
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© 2007 ASCE.
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Received: Jun 7, 2005
Accepted: Aug 23, 2006
Published online: Feb 1, 2007
Published in print: Feb 2007
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