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Geology topics

Richard M. Iverson

Publications and source records attributed to Richard M. Iverson.

88 records · Page 5Linked to original sources
USGS1997

Hydraulic modeling of unsteady debris-flow surges with solid-fluid interactions

Interactions of solid and fluid constituents produce the unique style of motion that typifies debris flows. To simulate this motion, a new hydraulic model represents debris flows as deforming masses of granular solids variably liquefied by viscous pore fluid. The momentum equation of the model describes how internal and boundary forces change as coarse-grained surge heads dominated by grain-contact friction grade into muddy debris-flow bodies more strongly influenced by fluid viscosity and pressure. Scaling analysis reveals that pore-pressure variations can cause flow resistance in surge heads to surpass that in debris-flow bodies by orders of magnitude. Numerical solutions of the coupled momentum and continuity equations provide good predictions of unsteady, nonuniform motion of experimental debris flows from initiation through deposition.

Conference Paper↗
USGS1995

Evaluation of viscoplastic slope movement based on triaxial tests

Viscoplastic soil parameters are used in a nonlinear viscoplastic constitutive model to predict time-dependent displacement of slow-moving landslides. The viscoplastic material parameters are determined by a novel method that uses a standard triaxial apparatus. This method employs data obtained from consolidated drained triaxial tests and consolidated drained stress-controlled strain-rate tests. The methodology was applied to undisturbed samples from the Minor Creek landslide in the Franciscan Terrane of northern California. Viscoplastic parameters determined from the laboratory tests were combined with boring log data to calculate the landslide’s vertical velocity profile. This profile provided a reasonable match to a measured velocity profile obtained from repetitive inclinometer surveys.

Book chapter↗
USGS1989

Dynamic pore-pressure fluctuations in rapidly shearing granular materials

Results from two types of experiments show that intergranular pore pressures fluctuated dynamically during rapid, steady shear deformation of water-saturated granular materials. During some fluctuations, the pore water locally supported all normal and shear stresses, while grain-contact stresses transiently fell to zero. Fluctuations also propagated outward from the shear zone; this process modifies grain-contact stresses in adjacent areas and potentially instigates shear-zone growth.

Science↗
USGS1987

The physics of debris flows — A conceptual assessment

Debris flows exhibit conspicuous dynamic interactions among their solid and fluid constituents. Key features of the interactions are neglected in traditional theories that treat debris flows as viscoplastic continua or as uniformly dispersed grain flows, but improved understanding of grain-grain and fluid-grain interactions has emerged from recent experimental and theoretical research. Grain-flow research has extended the concepts of statistical thermodynamics to consider inelastic grain collisions and to predict energy-dissipation, velocity, and grain-concentration distributions in flowing, granular materials. Research on fluid-grain interactions has focussed on fluctuating solid and fluid stresses in the vicinity of colliding grains and on energy dissipation in deforming solid-fluid mixtures. Insights born from these new approaches have practical ramifications for interpretive and predictive studies of debris flows.

Conference Paper↗
USGS1986

Unsteady, nonuniform landslide motion: 1. Theoretical dynamics and the steady datum state

Unsteady, nonuniform motion of persistently active landslides is a process of widespread importance. A general, three-dimensional theory aimed at elucidating this process is developed from physical principles and field measurements of landslide behavior. The theory employs a versatile constitutive model that represents landslides as deformable bodies composed of frictional, nonlinear viscoplastic material. The three-dimensional theory is reduced to a mathematically tracTable form by defining an ideal landslide datum state that consists of steady, unidirectional shear flow driven by ground-water seepage and gravitational forces. Solution of the datum-state equation of motion yields vertical landslide velocity profiles that can represent deformation styles ranging from shear-thickening viscoplastic flow to perfectly plastic frictional slip. This range of theoretical profiles encompasses the range of profiles measured in four persistently active northern California landslides. Also obtained from the datum-state equation of motion is an analytical solution for datum-state landslide sediment fluxes. An important feature of this solution is that it represents theoretical landslide sediment fluxes as a family of continuous-functions. The solution thus provides a mathematical basis for a general perturbation analysis of the kinematics of unsteady, nonuniform landslide motion, which will be presented in a companion paper in a subsequent issue of the Journal.

Journal of Geology↗
USGS1986

Unsteady, nonuniform landslide motion: 2. Linearized theory and the kinematics of transient response

Unsteady, nonuniform landslide motion is caused by temporal and spatial variations in driving and resisting forces. Common sources of these variations include stream undercutting of landslide toes, episodic headscarp slumping, and ground-water potentiometric fluctuations. A linear theory for the kinematics of unsteady, nonuniform landslide motion is developed here by analyzing the behavior of small perturbations about a datum state of steady landslide shear flow. The analysis indicates that local perturbations in landslide sediment flux exhibit advective-diffusive behavior that is controlled largely by a single dimensionless parameter, here called the landslide Peclet number. Explication of the physical meaning of this parameter shows that motion of landslide sediment-flux perturbations is dominated by slow advection if the landslide material behavior is primarily viscous and by rapid diffusion if the behavior is more rigidly plastic. Landslides that deform along thin plastic slip zones are thus inferred to respond relatively rapidly and globally to transient perturbations. Landslides that deform in thick zones of creeping flow, in contrast, are inferred to respond over periods as long as many tens of years, with zones of perturbed sediment flux that translate downslope as weakly diffusive kinematic waves. Many landslides probably fall between these two extremes in their style of response. The measured response of a large California landslide to transient toe undercutting by an adjacent stream helps corroborate the theoretical results.

California↗
USGS1985

A constitutive equation for mass-movement behavior

A phenomenological constitutive equation can serve as a basis for modeling and classifying mass-movement processes. The equation is derived using the principles of continuum mechanics and several simplifying assumptions about mass-movement behavior. These assumptions represent idealizations of field behavior, but they appear highly justifiable in light of the geomorphological insight that can be gained through modeling application of a mathematically tractable constitutive equation. The equation represents coupled pressure-dependent plastic yield and nonlinear viscous flow deformation components. The plastic yield component is a generalization of the Coulomb criterion to three-dimensional stress states, and the effect of pore-water pressures is accounted for by treating normal stresses as effective stresses. The nonlinear viscous flow component is a dimensionally homogeneous form of a three-dimensional power-law equation. Straightforward laboratory and field experiments can be used to estimate all plastic and viscous parameters in the constitutive equation. Reduction of the three-dimensional constitutive equation to two-and one-dimensional forms shows that it embodies, as special cases, many other constitutive models for mass movement. These include models of creeping, slumping, sliding, and flowing types of deformation. The equation may, therefore, serve as a conceptual basis for rheological classification of diverse mass-movement phenomena.

Journal of Geology↗