Collapse Mechanism of Compacted Clayey and Silty Sands

by T. A. Alwail, Ministry of Petroleum, Riyadh, Saudi Arabia,
C. L. Ho, (M.ASCE), Ministry of Petroleum, Riyadh, Saudi Arabia,
R. J. Fragaszy, (M.ASCE), Ministry of Petroleum, Riyadh, Saudi Arabia,

Document Type: Proceeding Paper

Part of: Vertical and Horizontal Deformations of Foundations and Embankments


The mechanism of wetting-induced collapse (hydrocompression) and the influence of fines ratios on compacted sandy soils are investigated. Various ratios of clay and silt are mixed with Ottawa sand to produce twenty-five soil combinations. Each soil is examined qualitatively under the Scanning Electron Microscope before and after collapse. Observed fabric alterations are supported by data obtained from Double-Oedometer Tests. Clay structures before collapse transform to a continuous or discontinuous clay blanket after collapse, depending on the initial clay quantity present in the soil. Magnitude of collapse increases with increasing clay/silt ratios. Silty sands with sharp silt grains and/or a higher clay content demonstrate greater collapse than soils with rounded silt grains and/or less clay content. This study suggests that collapse is profoundly influenced by the quantity of clay and the interaction of percolating water and the clay fractions of soils. A model showing fabric alterations of compacted clayey sands, silty sands, and clayey silty sands is presented.

Subject Headings: Clays | Compacted soils | Silt | Collapsible soils | Soil mixing | Sandy soils | Soil water

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