OCR Text |
Show Krasnosel'skii appears to make a series of questionable assumptions in order to equate basal and periphery effects. He assumes that the shear strength is comparable to the tensile strength and furthermore, for a slab thickness ( h ) and a semi- circular slab of radius ( R ), the basal area is^^^ and the periphery area isrffc. li . Only by equating the basal and periphery effects is he able to relate ( 7) to slab stability. The role of the periphery failure, as observations indicate, is insignificantly small in comparison to the basal failure; in those cases when the formation of cracks precedes the slab release, it is generally reduced to zero. The real insufficiency of Krasnosel'skii's method rests on the impossibility of predicting changes even in the immediate future for shear stress and strength. Although a measure of the margin of the shear strength over the shear stress may be a present indication of the hazard, it is not a forecast. Nonetheless, the proposed coefficient may be used in practice as an index of appropriateness for artificially releasing avalanches by means of explosives ( Maximov and Krasnosel'skii, 1964). Yu. D. Moskalev ( 1963) came to the conclusion that the avalanche danger for a given slope angle depends on the ratio between the bonding strength and the water content of the snow ( C/ vV ) and also on its coefficient of internal friction. From this he proposed a calculation of slab stability from a special nomogram and the avalanche danger from a chart of isolines based on snow and meteorological parameters. However, in order to determine the avalanche hazard it is necessary to measure CAA>' as well as the coefficients of viscosity on the avalanche- threatened slopes. Therefore, the method of Moskalev also requires measurements to be made with increasing frequency in the avalanche release zone during periods of high hazard to the observers. The most promising alternative for relatinq the avalanche hazard to meteorological factors and the experimental properties of the snow involves forecasting according to the amount of snow transported by wind ( Akkouratov, 1956). From many years of observation in the Khibiny, V. N. Akkouratov came to the conclusion that the majority of avalanches in that region resulted from wind drifting. Knowing the measured amount of snow transport ( gm cm~ 2min~') it is possible to find the times of onset and termination of the hazard on a specially prepared avalanche diagram. The corresponding formulae are t - m + 3 8 ( 8) - 5- |