International Symposium on Mitigative Measures against Snow ...

<strong>International</strong> <strong>Symposium</strong> on Mitigative Measures against Snow Avalanches
Egilsstaðir, Iceland, March 11–14, 2008
The maximum anchor tension forces during the winter 2006/07 have been recorded at the
upper anchor A3 and amount to 34 kN. The maximal measured tension forces in the uphill
wire ropes R2 and R3 range between 17 kN (R3) and 28 kN (R2), the maximal tension force
R4 in the wire rope that connects the head points of the posts is 24 kN.
The forces in the downhill wire ropes R6, R7 and R8 vary from 1 kN to 10 kN. The maximal
pressure force of 48 kN was recorded on the outermost post.
3.2 Numerical results
The following Table 1 depicts the forces in the Trumer net calculated according to the Swiss
guidelines and the method of Haefeli. On the stated days, the snow heights behind the nets
were measured with the terrestrial laser scanner. R4 represents the tension force in the wire
rope connecting the head points of the posts, R8 the tension force in the downhill guy, A3 the
tension force in the uphill anchor and P2x the pressure force in the post (see Figure 6). The
values in parenthesis are the corresponding measured forces.
Table 1 Calculated forces in the Trumer snow net on selected days during the winter
2006/07.
Date
H
[m]
ρ
[kg/m³]
R4
[kN]
R8
[kN]
A3
[kN]
P2x
[kN]
05.02.07 1.37 376 25.0 (12.1) 25.4 (4.4) 29.8 (26.1) 50.0 (21.5)
20.02.07 1.59 361 29.4 (14.3) 29.9 (5.6) 36.5 (27.3) 58.9 (25.1)
05.03.07 2.54 351 54.8 (18.9) 55.8 (5.8) 76.3 (29.4) 109.7 (32.2)
15.03.07 2.02 387 42.3 (19.1) 43.1 (8.4) 54.7 (31.7) 84.8 (24.3)
28.03.07 2.00 435 45.1 (23.5) 46.0 (2.4) 56.7 (32.6) 90.4 (46.4)
The calculated tension force in the wire rope R4 varies from 25.0 kN to 54.8 kN, the tension
force in the guy R8 from 25.4 kN to 55.8 kN and the tension force in the uphill anchor A3
from minimal 29.8 kN to maximal 76.3 kN. The results for the pressure forces P2x of the
interior post range from 50.0 kN to 109.7 kN. The minimum determined values correspond to
a snow height of 1.37 m, measured on 05.02.2007, the maximal calculated forces to a snow
height of 2.54 m on 05.03.2007.
The comparison of the calculated and measured forces depicts that the values determined with
the theoretical approach of Haefeli are consistently higher than the recorded field data. The
major difference between measured and calculated values results for the tension force R8 in
the downhill wire rope. The measured tension force R8 only amounts to about 20 % of the
calculated force. The calculated tension forces R4 and pressure forces P2x are almost twice
the amount of the corresponding measured values. The best accordance between calculated
and measured forces exists for the anchor tension force A3.
46 Snow loads on defensive snow net systems