Slow drag in wet-snow avalanche flow

Abstract

ABSTRACT. We report impact pressures exerted by three wet-snow avalanches on a pylon equipped with piezoelectric load cells. These pressures were considerably higher than those predicted by conventional avalanche engineering guidelines. The time-averaged pressure linearly increased with the immersion depth of the load cells and it was about eight times larger than the hydrostatic snow pressure. At the same immersion depth, the pressures were very similar for all three avalanches and no dependency between avalanche velocity and pressure was apparent. The pressure time series were characterized by large fluctuations. For all immersion depths and for all avalanches, the standard deviations of the fluctuations were, on average, about 20% of the mean value. We compare our observations with results of slow-drag granular experiments, where similar behavior has been explained by formation and destruction of chain structures due to jamming of granular material around the pylon, and we propose the same mechanism as a possible microscale interpretation of our observations.

The European mountain cryosphere: A review of past, current and future issues

“…The most destructive avalanches, moreover, mostly involve very cold and dry snow resulting from large snowfall, but may also result from wet snow events whose frequency has increased in the past . Recent results show that wet-5 snow avalanches indeed have a high damage potential due to their potentially long runouts and high impact pressures (Sovilla et al, 2010;Ancey, 2015). Hence, specific investigation of the rheology of such flows is required to realistically anticipate future changes in avalanche risk.…”

Wet-snow avalanche interaction with a deflecting dam: field observations and numerical simulations in a case study

“…Because of the low velocities and high flow depths, wet-snow avalanches generally interact with obstacles located in the run-out zone in a sub-critical flow regime (Sovilla et al, 2008). Recent investigations have shown that, in this flow regime, they can exert enormous forces in spite of their small velocities (Sovilla et al, 2010a(Sovilla et al, , 2008Baroudi et al, 2011). Furthermore, their flow is strongly influenced by rugged topography; they may spread out laterally forming finger and following small terrain irregularities regardless of the original flow direction, and may have a long run-out in spite of their low velocities (Sovilla et al, 2008;Kern et al, 2009).…”

Influence of snow cover properties on avalanche dynamics

“…Moreover, the different granular structures between wet and dry dense avalanches may also explain the significantly different pressures measured in the two flow typologies [Baroudi et al, 2011;Sovilla et al, 2010b]. Recently, it has been postulated that the pressure exerted by a wet-snow avalanche can be attributed to the formation and collapse of force-chain structures forming when the avalanche interact against an obstacle.…”