DEBRIS-FLOW MOBILIZATION FROM LANDSLIDES

Field observations, laboratory experiments, and theoretical analyses i ndicate that landslides mobilize to form debris flows by three process es: (a) widespread Coulomb failure within a sloping soil, rock, or sed iment mass, (b) partial or complete liquefaction of the mass by high p ore-fluid pressures, and (c) conversion of landslide translational ene rgy to internal vibrational energy (i.e. granular temperature). These processes can operate independently, but in many circumstances they ap pear to operate simultaneously and synergistically. Early work on debr is-flow mobilization described a similar interplay of processes but re lied on mechanical models in which debris behavior was assumed to be f ixed and governed by a Bingham or Bagnold theology. In contrast, this review emphasizes models in which debris behavior evolves in response to changing pore pressures and granular temperatures. One-dimensional infinite-slope models provide insight by quantifying how pore pressure s and granular temperatures can influence the transition from Coulomb failure to liquefaction. Analyses of multidimensional experiments reve al complications ignored in one-dimensional models and demonstrate tha t debris-flow mobilization may occur by at least two distinct modes in the field.