Discrete particle simulation of particulate systems: A review of major applications and findings

Persistent Scatterer Interferometry (PSI) is a powerful remote sensing technique able to measure and monitor displacements of the Earth’s surface over time. Specifically, PSI is a radar-based technique that belongs to the group of differential interferometric Synthetic Aperture Radar (SAR). This paper provides a review of such PSI technique. It firstly recalls the basic principles of SAR interferometry, differential SAR interferometry and PSI. Then, a review of the main PSI algorithms proposed in the literature is provided, describing the main approaches and the most important works devoted to single aspects of PSI. A central part of this paper is devoted to the discussion of different characteristics and technical aspects of PSI, e.g. SAR data availability, maximum deformation rates, deformation time series, thermal expansion component of PSI observations, etc. The paper then goes through the most important PSI validation activities, which have provided valuable inputs for the PSI development and its acceptability at scientific, technical and commercial level. This is followed by a description of the main PSI applications developed in the last fifteen years. The paper concludes with a discussion of the main open PSI problems and the associated future research lines.

https://zenodo.org/record/45568/files/Persistent_Scatterer_Interferometry.pdf

Persistent Scatterer Interferometry: A review

A squash ball almost doesn't bounce; a Superball bounces first left then right, seeming to have a mind of its own. Remarkable and complex elastic behavior isn't confined to sports equipment and toys. Indeed, it can be found in some surprising places. When the elastic behavior of a rock is probed, for instance, it shows extreme nonlinearity hysteresis and discrete memory (the Flint‐stones could have had a computer that used a sandstone for random‐access memory). Rocks are an example of a class of unusual elastic materials that includes sand. soil, cement, concrete, ceramics and, it turns out, damaged materials, Many members of this class are the blue‐collar materials of daily life: They are in the bridges we cross on the way to work, the roofs over our heads and the ground beneath our cities—such as the Los Angeles basin (home to many earthquakes). The elastic behavior of these materials is of more than academic interest.

Nonlinear Mesoscopic Elasticity: Evidence for a New Class of Materials

Physics of Flow through Porous Media

Smoothed particle hydrodynamics method for fluid flows, towards industrial applications: Motivations, current state, and challenges

The surface and downhole accelerations, and pore-water pressures recorded during the 1987 earthquakes at a site in the Imperial Wildlife Management Area (Imperial County, Calif.) are used to obtain direct estimates of the average seismic shear stress-strain and effective stress-path histories. These histories provide valuable insight into the site seismic behavior during liquefaction and associated loss of soil stiffness. As the pore pressure increases due to seismic excitation, site stiffness is found to gradually decrease. During the high-pore-pressure phase, site behavior is characterized by cycles of large shear strain and very small shear stress. At these large strains, evidence of hardening response, possibly due to a dilative-type soil behavior, is observed. The results of this study demonstrate that acceleration and pore pressure histories recorded by downhole arrays represent a valuable direct source of information on site response during seismic excitation.

Analysis of Site Liquefaction Using Earthquake Records

The characteristics of soil response during earthquake excitations, at a site in Lotung, Taiwan are identified using the Lotung large scale seismic test (LSST) data. A technique is developed to evaluate soil shear stress-strain histories directly from the free-field downhole accelerations. These histories are used to estimate variation of soil shear moduli and material damping characteristics with shear strain amplitude, and to assess the effects of pore pressure buildup. Soil stiffness properties are found to compare satisfactorily with those obtained through laboratory tests conducted by the University of California, Davis; the National Taiwan University; and the University of Texas at Austin. Pore pressure buildup appears to be accompanied by a reduction in soil stiffness. The information obtained in this study demonstrates that downhole accelerometer and pore pressure arrays offer a direct effective means of evaluating seismic soil properties.

Lotung Downhole Array. II: Evaluation of Soil Nonlinear Properties

The Lotung large-scale seismic test (LSST) site in Taiwan was instrumented in 1985 with an array of downhole and surface accelerometers, by the Electric Power Research Institute (EPRI), Palo Alto, Calif., and the Taiwan Power Company (TPC), Taipei, Taiwan. A total of 18 earthquakes were recorded during the period 1985–86. Correlation and spectral analyses of the recorded downhole accelerations are performed to evaluate shear wave propagation characteristics, variation of shear wave velocity with depth, and site resonant frequencies and modal configurations. A shear-beam model, calibrated by the identified site properties, is found to represent the site dynamic response characteristics over a wide frequency range. In a companion paper, strong-motion earthquake records are utilized to investigate the Lotung site large-strain soil response characteristics.

Lotung Downhole Array. I: Evaluation of Site Dynamic Properties

Widespread liquefaction occurred in Kobe, Japan, during the 1995 Hyogoken-Nanbu earthquake. At the reclaimed Port Island in Kobe, the observed large-scale liquefaction was documented by acceleration records from a downhole seismic array. Four accelerometers recorded the soil stratum response, from the ground surface down to a depth of 83 m. These recorded accelerations are used here to obtan direct estimates of the corresponding seismic shear stress and strain histories within the soil layers, which shed light on (1) the site seismic response during liquefaction and associated loss of soil stiffness at shallow depths near the ground surface; and (2) the virtually linear site response at deeper elevations. Response of the liquefied upper layer is characterized by cycles of large shear strain and very small shear stress. Conversely, the lower strata exhibited no sign of stiffness degradation throughout the earthquake. A computational simulation of this case history is performed in order to assess the mechanisms of site amplification and excess pore-pressure buildup. The results of this study demonstrate that acceleration histories recorded by downhole arrays represent a valuable direct source of information on site response during seismic excitation.

Liquefaction of reclaimed island in kobe, japan

A coupled hydromechanical model was used to analyze the mesoscale pore fluid flow and microscale solid phase deformation of saturated granular soils. The fluid motion was idealized using averaged Navier-Stokes equations, and the discrete element method was employed to model the assemblage of solid particles. The fluid-particle interactions were quantified using established semiempirical relationships. Simulations were conducted to investigate the three-dimensional response of sandy deposits when subjected to critical and overcritical upward pore fluid flow. These simulations revealed complex response patterns after the onset of quicksand conditions and provided valuable insight into the associated mechanisms. The employed model provides an effective tool to assess the microscale mechanisms and characteristics of the partially drained response of saturated granular media.

Mourad Zeghal

Papers

Analysis of Site Liquefaction Using Earthquake Records

Lotung Downhole Array. II: Evaluation of Soil Nonlinear Properties

Lotung Downhole Array. I: Evaluation of Site Dynamic Properties

Liquefaction of reclaimed island in kobe, japan

Coupled continuum-discrete model for saturated granular soils