. Mechanics of debris avalanching in shallow till soils of southeast Alaska. Soil mechanics Alaska; Landslides Alaska; Debris avalanches Alaska. Under the assumed conditions, C is a constant and AL or thickness of the soil mass is unity. Wn is also unity, and cf> is constant. With decreasing slope, sin a decreases faster than cos a • The F value correspondingly increases as the slope gets smaller. This points up the strong relationship between slope angle and slide susceptibility. Strahler (1956) has developed a method of slope analysis that expresses this relationship particularly well. By
. Mechanics of debris avalanching in shallow till soils of southeast Alaska. Soil mechanics Alaska; Landslides Alaska; Debris avalanches Alaska. Under the assumed conditions, C is a constant and AL or thickness of the soil mass is unity. Wn is also unity, and cf> is constant. With decreasing slope, sin a decreases faster than cos a • The F value correspondingly increases as the slope gets smaller. This points up the strong relationship between slope angle and slide susceptibility. Strahler (1956) has developed a method of slope analysis that expresses this relationship particularly well. By determining the sines of the slope angles for a large number of points in an area, an isosinal map can be made by con- touring the values. For cohesionless soils, the sine of the slope angle repre- sents that part of the total gravitational force acting to produce downhill sliding or flowage of rock particles or fluids on the surface. A soil particle located at point "P" on the slope is affected by forces Fg = mg. , where m is mass in pounds and g is the acceleration of gravity in feet per second per second, Fg is shear stress (x) in pounds per square foot. Fs and Fn are components of Fg. The elementary trigonometric relationship of the principal forces acting on a soil particle on a slope (Strahler 1956) is depicted in figure 7. Figure 7.—Principal forces acting on a soil particle on a slope (after Strahler 1956). Fg represents the force of gravity acting on the particle, Fs is the shear stress, and Fn is the force normal to the surface, a is the angle of slope and <p is the angle of internal F sin (j> = _s- -L_, by geometry, a = $. F„ F § g When a unit mass of soil surrounding point "P" on the slope is considered, the downslope force [shear stress (t)] operating on that mass is given as t = F sin a, the equation for the shear stress in a cohesionless soil. Note that Fg in this case represents the column or weight of material. Thus,
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