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Show Shearing action takes place at planes of layer contact; and where there is an ice crust between layers, it is often displaced with the shorn layer. Windblown snow, particularly, is transformed into fine granular snow; and this is why such snows show slightly lowered values for intermittent shearing strength in Table 4. Resistance to intermittent tension was measured by means of an open metal collar with a free 10 x 10 cm section operating on the principle of Michaelis1 apparatus for tensile strength tests of concrete. Tensile strength of layers of loose recrystallized snow is 2- 4 times less than the shearing strength of the same snow; but in firm snow that has not recrystallized, the reverse may be the case. Resistance to intermittent crushing was measured by the use of snow cylinders 8 cm in both height and diameter installed on a small hanging square ( plaque) and applying pressure toward the fixed upper surface of the device. Crushing strength is 2- 4 times greater than the shearing strength for the same snow. Observations showed that the degree of resistance to mechanical forces depends essentially on the structure and the type of bond of the snow. Density can be a criterion of strength ( firmness, solidity) only in snow of the same structure. Thus, granular snow of density 0.25 can be easily destroyed by slight pressure, whereas windblown snow of the same density can resist considerable stress. For the compression of snow under load we used a cylinder with a cross-sectional area of 50 cm2 . Pressure was applied to the snow specimen by a wooden piston of the same diameter as the cylinder ( i. e., to clear) with a weight table at its upper end. Compression was not steady, but was applied in uneven graduations, often in rapid succession. Only freshly fallen snow is more or less easily compressed, and then only within certain limits. Changes taking place in dense snow under load, even heavy load, are insignificant. Changes in density ( average of 3- 12 measurements) for one series of observations are shown in Table 5. Table 5 Snow Changes in Density of Snow Under Load Load ( g/ cm2) Loose, fine granular Loose, unbound granular ( grains to 1 mm) Loosely bound granular ( grains to 1- 2 mm) Dense granular 0 40 80 120 200 280 400 0.20 0.29 0.32 0.33 0.37 0.38 0.39 0.24 0.27 0.28 0.32 0.33 0.33 0.37 0.28 0.30 0.32 0.34 0.39 0.40 0.40 0.33 0.33 0.33 0.34 0.34 0.36 0.38 - 28- |
