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Volcanic soil properties in Dominica, West Indies
Abstract The unusual geotechnical and hydrological characteristics of the tropical clay soils involved in landslides in Dominica resulting from hurricanes David and Frederic in 1979 are examined. These highly porous soils exhibit very high field moisture contents (42–180% for allophane latosols), void ratios are very high (up to 6 for allophanes) and therefore field dry unit weights are very low (5.47–10.01 kN/m3 for allophanes). Although predrying does not greatly affect the Atterberg limits of kandoids, it causes great reductions in the limits of allophane-rich soils, the degree of difference depending on the allophane content. Allophane soils also form a distinct group on Cassagrande's plasticity chart, falling below the A-line as liquid limit increases. Predrying increases the ′r values by around 7° for kandoids but does not affect the allophanes and smectoids. Values of ′r vary with clay mineralogy — allophanes 30–38°, smectoids 32–35°, “dry” kandoids 33–34°, “wet” kandoids 25–29°. All are abovevalues for temperate clays and are more akin to granular soils. None of the direct shear tests showed any change of τ ′/σ′n as σ′n n increased — a marked contrast to temperate clays. A detailed understanding of runoff processes, notably zones of percolation impedance, perched saturation and throughflow, is essential to explanations of slope failure patterns. Although topsoil permeabilities and porosities of all Dominican soils are extremely high, subsurface soil hydrology varies strikingly with soil type. Impermeable subsoils and pans impede percolation at a shallow depth in smectoid and allophane podzolic soils. In kandoids and allophane latosolics two zones of impedance (above the B horizon and at the soilk—rock interface) are important, but sufficient vertical development of saturation zonesto initiate landslides can only occur in the exceptionally prolonged high-intensity rainfalls of cyclones.
Volcanic soil properties in Dominica, West Indies
Abstract The unusual geotechnical and hydrological characteristics of the tropical clay soils involved in landslides in Dominica resulting from hurricanes David and Frederic in 1979 are examined. These highly porous soils exhibit very high field moisture contents (42–180% for allophane latosols), void ratios are very high (up to 6 for allophanes) and therefore field dry unit weights are very low (5.47–10.01 kN/m3 for allophanes). Although predrying does not greatly affect the Atterberg limits of kandoids, it causes great reductions in the limits of allophane-rich soils, the degree of difference depending on the allophane content. Allophane soils also form a distinct group on Cassagrande's plasticity chart, falling below the A-line as liquid limit increases. Predrying increases the ′r values by around 7° for kandoids but does not affect the allophanes and smectoids. Values of ′r vary with clay mineralogy — allophanes 30–38°, smectoids 32–35°, “dry” kandoids 33–34°, “wet” kandoids 25–29°. All are abovevalues for temperate clays and are more akin to granular soils. None of the direct shear tests showed any change of τ ′/σ′n as σ′n n increased — a marked contrast to temperate clays. A detailed understanding of runoff processes, notably zones of percolation impedance, perched saturation and throughflow, is essential to explanations of slope failure patterns. Although topsoil permeabilities and porosities of all Dominican soils are extremely high, subsurface soil hydrology varies strikingly with soil type. Impermeable subsoils and pans impede percolation at a shallow depth in smectoid and allophane podzolic soils. In kandoids and allophane latosolics two zones of impedance (above the B horizon and at the soilk—rock interface) are important, but sufficient vertical development of saturation zonesto initiate landslides can only occur in the exceptionally prolonged high-intensity rainfalls of cyclones.
Volcanic soil properties in Dominica, West Indies
Rouse, W.C. (author) / Reading, A.J. (author) / Walsh, R.P.D. (author)
Engineering Geology ; 23 ; 1-28
1986-02-24
28 pages
Article (Journal)
Electronic Resource
English
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