HR: 15:10h
AN: H43G-07    [Abstracts]
TI: Regulation of Landslide Motion by Dilatancy and Pore-pressure Feedback
AU: * Iverson, R M
EM: riverson@usgs.gov
AF: USGS, 1300 SE Cardinal Ct. \#100, Vancouver, WA 98683 United States
AU: Schaeffer, D G
EM: dgs@math.duke.edu
AF: Duke University, Dept. of Mathematics, Durham, NC 22708 United States
AB: A new mathematical model demonstrates how diverse styles and rates of landslide motion can result from regulation of basal Coulomb friction by dilation or contraction of water-saturated basal shear zones. Normalization of the model equations shows that feedback due to coupling between landslide motion, shear-zone volume change, and pore-pressure change depends on a dimensionless parameter $\alpha$, which in turn depends on the dilatancy angle $\psi$ and the intrinsic time scales for pore-pressure generation and dissipation. If soil in the shear zone contracts during slope failure, then $\alpha$ $<$ 0 and positive pore-pressure feedback and runaway acceleration are inevitable. If the shear-zone soil dilates, then $\alpha$ $>$ 0 and negative feedback permits slow, steady landslide motion to occur while rain infiltration supplies positive pore pressure. Predicted steady-state slip velocities v obey v = -(K/$\psi$)p , where K is the shear-zone hydraulic conductivity and p is the normalized (dimensionless) negative pore pressure generated by dilation. If pore-pressure buildup due to rain infiltration continues unabated, or if shear-zone soil density approaches a steady state (i.e., if $\psi$ decays to zero) as landslide motion proceeds, then slow stable motion eventually gives way to unbounded acceleration. Furthermore, if basal Coulomb friction decreases as a function of slip rate, landslide motion can exhibit stick-slip instabilities. Such instabilities occur only in a particular region of a two-dimensional parameter space defined by $\alpha$ and a dimensionless friction decay constant, r. Within the $\alpha$ - r parameter space, changes from stable to unstable sliding are manifestations of a Hopf bifurcation, which explains why seemingly similar landslides can exhibit disparate behavior.
DE: 3210 Modeling
DE: 3220 Nonlinear dynamics
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
DE: 1829 Groundwater hydrology
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting