J. P. Bardet

The slump origin of the 1998 Papua New Guinea Tsunami

The origin of the Papua New Guinea tsunami that killed over 2100 people on 17 July 1998 has remained controversial, as dislocation sources based on the parent earthquake fail to model its extreme run–up amplitude. The generation of tsunamis by submarine mass failure had been considered a rare phenomenon which had aroused virtually no attention in terms of tsunami hazard mitigation. We report on recently acquired high–resolution seismic reflection data which yield new images of a large underwater slump, coincident with photographic and bathymetric evidence of the same feature, suspected of having generated the tsunami. T–phase records from an unblocked hydrophone at Wake Island provide new evidence for the timing of the slump. By merging geological data with hydrodynamic modelling, we reproduce the observed tsunami amplitude and timing in a manner consistent with eyewitness accounts. Submarine mass failure is predicted based on fundamental geological and geotechnical information.

Observations on the effects of particle rotations on the failure of idealized granular materials

Abstract Based on the computer simulations of biaxial tests, particle rotations are shown to have little influence on the elastic properties of idealized granular materials, but significant effects on their shear strength. The overall peak and residual friction angles, op and or, are smaller than the interparticle friction angle oμ because of the concentration of rotations in shear bands. When particle rotations are artificially prevented, op and or, become larger than oμ and the localized failure patterns become different from those observed experimentally in granular media. The average particle rotation remains small in the complete biaxial specimen, but increases in shear bands. The particle rotations follow an exponential distribution independent of the axial strain. Particle rotations induce twice as many rolling contacts as sliding contacts. Compared to sliding contacts, rolling contacts are oriented differently, generate different fabric tensors, and are less capable of dissipating energy and supporting inclined contact forces.

The asymmetry of stress in granular media

Here, we show that the average stress in granular media, which is defined from virtual work, may be asymmetric in the absence of contact moments. We specify the circumstances and amplitude of stress asymmetry, and calculate the corresponding couple stress and first stress moment. We also show that the average stress is always symmetric, when it is alternately defined by using statics and no contact moment. The stress asymmetry, which results from external moments, has an amplitude that decreases with the volume size. The present analysis applies to two- and three-dimensional particles of arbitrary shapes. The asymmetric stress, couple stress and first stress moment are analytically calculated in a particular example with cylindrical and spherical particles.

Lode Dependences for Isotropic Pressure-Sensitive Elastoplastic Materials

Experimental investigations indicate that the third stress invariant; Lode angle α affects significantly the behavior of pressure sensitive materials. The present communication presents a formulation to account for α in isotropic pressure-sensitive elastoplastic materials. Seven Lode dependences are reviewed

A practical method for solving free-surface seepage problems

Abstract Free-surface (unconfined) seepage problems are commonly encountered in geotechnical engineering. In these problems, the determination of the free surface usually requires sophisticated numerical techniques, unfamiliar to most engineers and students. Herein we present a practical finite difference method for unconfined seepage, which can be easily implemented in spreadsheets. The finite difference equations are based on the concepts of extended pressure and flux conservation. The method is illustrated by several free-surface seepage problems previously analyzed with more sophisticated numerical techniques. The proposed method eliminates the formation of matrix systems at the expenses of slower convergence rate for large problems. It has not only educational but also practical values as it applies to various engineering problems.

A comprehensive review of strain localization in elastoplastic soils

Abstract The paper reviews the theory of strain localization for elastoplastic soils and relates it to past works on the inclination of shear bands. It outlines and discusses the main theoretical assumptions, describes the localized velocity field, compiles experimental results and compares them to theoretical predictions on shear band orientations. It studies the effect of elastic unloading and examines systematically the influences of friction angle, dilatancy angle, Poissons ratio and hardening modulus on shear bands. After comparing the predictions of the Mohr-Coulomb and Drucker-Prager models, the study concludes that the application of the strain localization theory to elastoplasticity does not account for the observed shear band orientations in all circumstances. It also recalls that the strain localization theory provides a necessary, but not sufficient, condition for the emergence of shear bands, a theoretical feature which enhances the disagreement between the experimental observations and theoretical predictions on shear band inclinations.

A Viscoelastic Model for the Dynamic Behavior of Saturated Poroelastic Soils

4 viscoelastic model is proposed to describe the dynamic response of the saturated poroelastic materials that obey the Biot theory (1956). The viscoelastic model is defined from the velocity and attenuation of dilatational and distortional waves in poroelastic materials. Its material properties are defined in terms of the elastic moduli, porosity, specific gravity, degree of saturation, and permeability of the soils. The proposed model is tested by comparing its response with the one of poroelastic materials in the case of axial and lateral harmonic loadings of onedimensional columns. The viscoelastic model is simpler to use than poroelastic materials but yields similar results for a wide range of soils and dynamic loadings.

Regional Modeling of Liquefaction- Induced Ground Deformation

Liquefaction-induced ground deformations are permanent ground displacements resulting from earthquakes, which can extend over areas as large as a few square kilometers and have amplitudes ranging from a few centimeters to few tens of meters. This type of ground deformation caused substantial damage to lifelines and pile-foundations of buildings and bridge piers along the Kobe shoreline during the 1995 Hyogoken-Nanbu, Japan, earthquake. This paper presents a four-parameter multiple-linear-regression model for estimating the amplitude of liquefaction-induced ground displacement for both ground-slope and free-face conditions at a regional scale. The applicability of the model for mapping the amplitude of liquefaction-induced ground deformation is investigated over selected regions. The paper also presents a regional model for estimating the probability for the displacements to exceed some threshold amplitude, and to fall within confidence intervals. Both models are useful for risk assessment to spatially distributed lifeline networks resulting from future earthquakes.

Adaptative dynamic relaxation for statics of granular materials

A numerical technique based on adaptative dynamic relaxation (ADR) is proposed to study the statics of granular materials. Calibrated with the locally and globally dominant modes of granular assemblages, ADR provides the optimum rate of convergence of conditionally stable explicit algorithms, automatically adjusts the algorithm parameters, and eliminates the introduction of artificial damping coefficients.

Introduction to Computational Granular Mechanics

The first discrete modeling of soils can be traced to Hertz [90] who formulated a contact law between spheres, and Reynolds [167] who proposed a dilatancy theory. Dantu [55] and Schneebli [180] idealized real soils as assemblies of rigid rods, and noticed some striking similarities between the mechanical responses of these mechanical analogs and real soils. Duffy and Mindlin [70], Deresiewicz [59, 60], and Thurston and Deresiewicz [204] examined the response of soil models made of spheres. Biarez [21] used glass beads and duralumium rods to examine the elastic and limit response of soils, and applied his observations to analyze practical problems in geotechnical engineering. These pioneer works were later followed by photoelastic investigations [e.g., 67, 68] to visualize stresses within granular media.