. Mechanics of debris avalanching in shallow till soils of southeast Alaska. Soil mechanics Alaska; Landslides Alaska; Debris avalanches Alaska. 8 / within the range of expected unit weight values for the Karta soil â ' and will be used in this paper as an index of the unit weight of the slide-prone soils. PORE-WATER PRESSURE MEASUREMENTS Pore-water pressure measurements during the fall rainy season (September through November) were begun in 1964 and continued in 1965 (Swanston 1967a, b). Direct correlation of both the 1964 and 1965 field data with rainfall variations recorded in the valley in
. Mechanics of debris avalanching in shallow till soils of southeast Alaska. Soil mechanics Alaska; Landslides Alaska; Debris avalanches Alaska. 8 / within the range of expected unit weight values for the Karta soil â ' and will be used in this paper as an index of the unit weight of the slide-prone soils. PORE-WATER PRESSURE MEASUREMENTS Pore-water pressure measurements during the fall rainy season (September through November) were begun in 1964 and continued in 1965 (Swanston 1967a, b). Direct correlation of both the 1964 and 1965 field data with rainfall variations recorded in the valley indicate a close relationship between these parameters. A more detailed regression analysis of the 1965 field data (Swanston 1967b) revealed a curvilinear relationship between rainfall, pore-water pressure, and slope position, allowing us to make direct approximations of prevailing piezo- metric levels at the time and point of initiation of known landslide activity (fig. 4) Within the three selected study areas, rainfall conditions and slope position at the time of initial slope failure indicate conditions of total soil saturation to be in effect. Thus, for purposes of slope analysis, we can assume that the slide- prone soils were subjected to maximum pore-water pressures at the time of initial slope failure. Freeman Stephens, Soil Scientist, U. S. Forest Service Region 10, personal communication. Mr- Figure 4.âCurvilinear relationship of average piezometric head vs. rainfall for two slide- prone slope locations. Curve A represents piezometric head on the open slopes; Curve B represents piezometric head within linear drainage depressions (after Swanston 1967b). CURVE: CURVE: A. j_ -L 1 2 3 4 5 RAINFALL (inches/day) â1208 182 156^ \ 130""" LU to 104 £ a. 78 £ i â LU 52 a> o a_ 26 7. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrat
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