OCR Text |
Show usual manner, only insignificant damage occurred in the stand of trees. A further difference compared with the other avalanches lay in the composition of the snow mass. In the Esch gulch the snow was mixed rather uniformly thruout the entire depth with wood fragments, earth, and stones, while in the other avalanches, in spite of very large snow depth in some cases, for example, in the dammed up zone at the Dalaas rail station, the debris lay localized at the time in the vicinity of the destroyed objects or spread at a certain distance on the surface of the snow. These observations permit one to conclude that, in this " channeled" avalanche, the pushing effects were materially greater than in loose snow avalanches sliding on an open slope. This avalanche may be considered to be the one with the greatest forces in that region under the existing conditions. Indicators for the limits of the forces are, first, a piece of railroad rail, which served as a post for a handrail and remained intact, and consequently gives a limiting value which was not reached, and furthermore, broken off tree trunks, which indicate the lower boundary value that was exceeded. The static calculation shows that the stress of about 6000 kg/ m2 projected on a round timber was exceeded. A structural steel support, shown in Figure 8, which had been erected for a projected cable way, the cable of which had not yet been installed, was bent over sideways. A static stress of about 3500 kg/ m2 is necessary to bend it in the direction shown, see Figure 8a. Fig. 8a. Structural steel support bent down by the avalanche. Foundation wall of a house under construction in Blons ( Figure 9). In this instance the construction work had been stopped after the excavation had been dug and the four concrete foundation walls had been poured. The object was consequently like a box, open at the top, placed horizontally on the slope in such a way that the back wall was completely and the side- walls were partially surrounded by earth and only the front wall on the valley side stood free. The slope extended with a rather uniform inclination ( about 30<>) and without significant barriers more than 700 to 1000 meters upwards to the forest boundary. The concrete wall on the valley side was torn away from the side walls and turned over by the avalanche, but, in spite of the inclination of the slope, it was moved only about 4 meters. The calculated thrust to break away this wall, assuming a tensile strength of 15 to 20 kg/ cm2 for the concrete, amounts to a total of about 100 to 150 tons, corresponding to 3000 to 5000 kg/ m2 of wall area |