ABSTRACT
Motion of large, complex, persistently active, earthflow-like landslides commonly varies in time and space. Unusually good documentation of such unsteady, nonuniform landslide motion is provided by a 12-year record of the behavior of Minor Creek landslide in northwestern California. Based on inferences drawn from Minor Creek landslide data and on deductions drawn from general physical principles, a mathematical theory of unsteady, nonuniform landslide motion is developed. The theory employs a generalized constitutive model that can represent landslide deformation styles ranging from “dilatant” viscoplastic flow to rigid-plastic frictional slip. A perturbation analysis, which embodies the generalized constitutive model and departs from equations that reflect steady landslide shear deformation, is used to investigate unsteady, nonuniform landslide motion. The analysis shows that transient, localized perturbations in landslide motion propagate slowly downslope as kinematic waves and spread rapidly outward by diffusion. The importance of perturbation propagation relative to perturbation diffusion is dictated principally by the value of a single dimensionless parameter, called the landslide Peclet number. This number can be expressed as an algebraic function of landslide physical properties, and its value appears to hold major implications for landslide behavior. The transient response of Minor Creek landslide to an episode of toe erosion can be explained by applying the perturbation theory and evaluating the landslide Peclet number.
