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Show Y0 in the preceding equation. The compression of the air in the pores of the snow can be considered to be isothermal since the heat developed is immediately absorbed by the snow. According to Boyle- Mariotte: ( Po + P) VL = Po ( YF - Yo)/ Y F = PoVLO ( 1 8 " ) VL= P o / ( P o + P} * ( Y F - Y O } / YF Under the dynamic overpressure p ( greater than p0 = 1 atmosphere) the density of the snow ( weight/ compressed volume) is: ( 19) Yd = Y0/( 1 + VL - VL0) - Y 0 ( 1 + P/ Po} / ( 1 + Y O P / Y F PO} The dynamic pressure head amounts to: JP° X/ Y = P/ YF +( po ' Y o} * ( l ~ Y J Y ) InU + P/ P0 ( 20) } P, as an example, for Y0= 300 . kg/ m3 . Po= 10' 000 k g / m 2 yF= 800 kg/ m , p = 10,000 kg/ m Po + P / 3 [ dp/ Y = 27.0 m = p/ Y m; that is Y m = 370 kg/ m ^ Po According to Equation ( 19) under the dynamic pressure p = 10,000 kg/ m2 Y * - 436 kg/ m3. The average value during the compression amounts to: ( 21). Ym = ( Y / YH)/ 2= Yn+( Y n/ 2)( l+ Y Q/ Y F) P/ PQ ( 1 + Y 0P/ Y FPo > In the preceding case Y m = 368 kg/ m3; in other words the pressure calculation may be carried out using Y m from Eq" atlon ( 2 1 ) as for an incompressible material. The static compressibility of snow is dependent in a complicated way upon the magnitude and duration of the pressure as well as upon the temperature, the character of the snow, and metamorphism. A fairly correct picture of the actual behavior can be obtained byvthe hypothesis that the compression of the air in the pores, bought about first by the pressure, is equalized during settlement of the snow material. Then, without altering the settlement which has taken place, the air in the pores escapes. 35 |