On the onset of avalanches in flooded loose sand

Loose hooded and nearly saturated sand deposits from lignite mining in East Germany tend to collapse along slopes, leading to devastating avalanches. The local state of the soil is characterized by volume fractions and partia l stresses as is usual in soil mechanics. In addition, an intergranular str ain is introduced that is needed for the analysis of wave propagation. For the investigation of the field state in situ, frozen samples have sometimes been taken, and three novel sounding methods have been introduced: vibrato ry penetration; large vane with torsion shocks; and pressure shocks by airg un. The evolution of field states is described by a hypoplastic constitutiv e relation, the parameters of which can be estimated from granulometric pro perties. The influence of gas bubbles on the response to undrained loading cycles is explained. The loss of stability can be analysed by estimating th e possible spontaneous release of kinetic energy, whereas conventional meth ods are insufficient. A deeper understanding of the loss of stability is ob tained by analysing the propagation of transversal and longitudinal waves w hich are coupled by dilatancy or contractancy. Finally, a scenario for the onset of an avalanche is proposed that includes the formation of a gas cush ion.