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Show greater height and strength of the individual structures, so far as the technical aspects alone are concerned. E. Wedge- shaped buffers are stressed less, but also are less effective than buffer walls arranged at right angles to the avalanche path. All of these buffer structures are ineffective in protecting the structures lying below against powder avalanches. Experience indicates in this regard that an insufficient size of the structures cannot be outweighed by greater numbers of them, whether it is a matter of buffer and diversion structures or of obstructions in the release zone. If the latter are not high enough to prevent the formation of surface avalanches, they can cause avalanches [ 19], especially if they favor the formation of higher snow drifts in their vicinity. Defense structures in the release zone of avalanches have given heretofore no certain protection against the formation of avalanches in their area, since earlier they were usually constructed too low and too wide [ l], [ 3]. However, modern obstructions have generally stood the test in recent periods of catastrophe. The observations described in Section IV, 2, show that indeed small snow slides can exert considerable dynamic impact and lifting forces on obstructions [ Equations ( 3), ( 5), ( VIII), ( IX)]. Also the creep pressure, in its final state after reaching the upper limiting value for equilibrium by side thrust, can acquire fundamentally upward directed components, which to be sure cannot as yet be measured but can probably be observed [ l6]. It is, at the very least, not advisable to base the margin of safety of static calculations on a downward acting component of creep pressure. Without exception up to now damage observed to supporting structures of various kinds and of various materials was caused primarily by lifting and shifting of the foundation on the side toward the mountain. A substantial increase in the margin of safety is to be expected by connecting the mountain side foundation of the post beam and the valley side foundation of the support by means of a tie rod. In special cases, which exceed the range of validity of creep research up to now [ 6], [ 7], the maximum possible creep pressure can be estimated by the methods of calculating passive soil pressure [ l7_, [ 20]. The spacing of individual units of constructions is limited by the requirement that an angle of repose 9 between the snow and the ground ought not be exceeded. This corresponds to a slope inclination of Y R ~ < P ~ 25, below which no avalanche releases have yet been observed. Exceeding the angle of repose will cause greater slip movement of snow, which can lead, in the course of creep, to exceeding the limiting value for the internal equilibrium of the snow and to damming of the same in front of the supporting structure. This brings to play dangerous upward directed forces. If the supporting structure, set approximately perpendicular to the slope, is rated for the creep pressure K kg/ m* of snow density Ymax kg/ m3 with a factor of safety n, the spacing L of the individual units may not, from the above requirement and geometrical considerations of equilibrium, exceed the following value: L <( Kn/ Y m a x ) ( cos< p/ sin( Y - < P )) If L is chosen larger, greater forces must be absorbed. Also the uppermost structure should have, at most, a spacing L from a 60 |