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

We present a new empirical ground motion model for PGA, PGV, PGD and 5% damped linear elastic response spectra for periods ranging from 0.01– 10 s. The model was developed as part of the PEER Next Generation Attenuation (NGA) project. We used a subset of the PEER NGA database for which we excluded recordings and earthquakes that were believed to be inappropriate for estimating free-field ground motions from shallow earthquake mainshocks in active tectonic regimes. We developed relations for both the median and standard deviation of the geometric mean horizontal component of ground motion that we consider to be valid for magnitudes ranging from 4.0 up to 7.5–8.5 (depending on fault mechanism) and distances ranging from 0 – 200 km. The model explicitly includes the effects of magnitude saturation, magnitude-dependent attenuation, style of faulting, rupture depth, hanging-wall geometry, linear and nonlinear site response, 3-D basin response, and inter-event and intra-event variability. Soil nonlinearity causes the intra-event standard deviation to depend on the amplitude of PGA on reference rock rather than on magnitude, which leads to a decrease in aleatory uncertainty at high levels of ground shaking for sites located on soil. DOI: 10.1193/1.2857546

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NGA Ground Motion Model for the Geometric Mean Horizontal Component of PGA, PGV, PGD and 5% Damped Linear Elastic Response Spectra for Periods Ranging from 0.01 to 10 s

Data are presented concerning the shear modulus and damping ratios of sands and gravelly soils as determined by laboratory and field tests. A simple relationship is proposed to relate the shear modulus of a cohesionless soil to a modulus stiffness coefficient, which is a soil property and depends on the characteristics of the soil, and the effective mean principal stress at any point in the soil. Values for the modulus coefficient at low strains are suggested, and it is shown that these values for sands can be estimated from the standard penetration resistance of the sand. Values for gravels are generally greater than those for sands by factors ranging from 1.35–2.5. Suggestions are also made for determining the variation of shear modulus with shear strain and the damping ratios for both sandy and gravelly soils.

Moduli and Damping Factors for Dynamic Analyses of Cohesionless Soils

Development of a new family of normalized modulus reduction and material damping curves

Unified dynamic shear moduli and damping ratios of sand and clay

In this paper the writers first present experimental results obtained for the distribution of the active stresses due to a sand backfill behind a rigid wall rotating about the top. The experimental evidence shows that the stress distribution is nonlinear and that, due to arching, the stress near the top of the wall increases beyond the level of the at‐rest stress. Consequently, the point of application of the lateral thrust is much higher than one‐third from the wall base. Arching effects increase with increasing soil density. Secondly, comparisons of the active earth pressure distributions are made for three different wall movement modes: (1) Rotation about top; (2) rotation about heel; and (3) translation. Total active resultant forces and the points of application of these forces are summarized.

Static earth pressures with various wall movements

This paper outlines the results of unique shaking table experiments to determine neutral and active static and dynamic stresses and the points of application of corresponding total thrust generated by granular soils against rigid retaining walls and compares the experimental data with the well-known Coulomb and Mononobe-Okabe equations. A new criterion is proposed for identification of the wall deformation level at which the active state of stress develops. This criterion states that active stress develops when the angle of friction between the wall and the backfill soil reaches its maximum value. Based on the above criterion, experimental results show that the backfill soil enters the active state at much lower wall displacement levels than generally believed. An equation is proposed for calculating the displacement necessary to initiate active static or dynamic stress. This equation reveals that the displacement necessary to initiate active state increases with the height of the wall and decreases with backfill soil strength.

Earth Pressures against Rigid Retaining Walls

Soil liquefaction has become an important consideration in the design of structures in seismically active regions. Many researchers have in the past attempted to determine the liquefaction potential of soils, but these studies concerned themselves with the liquefaction potential of fully saturated sands. In this paper, the writers establish a general relationship between the pore-pres-sure parameter, B and the initial degree of soil saturation, S o . By introducing the experimental values of B obtained from tests on loose Ottawa sand.

Saturation Effects on Initial Soil Liquefaction

Current theories and procedures in evaluating dynamic lateral earth and water pressures due to submerged backfill soils against rigid retaining structures are thoroughly reviewed. Available experimental data is gathered and compared to the theories. A new generalized apparent angle of seismic coefficient, which can be easily used to evaluate dynamic soil as well as water pressure for a wide range of backfill soil types, is proposed. The new procedure incorporates the effect of the permeability and the geometry of the backfill soils and the modes of the wall movement.

Isao Ishibashi

Papers

Unified dynamic shear moduli and damping ratios of sand and clay

Static earth pressures with various wall movements

Earth Pressures against Rigid Retaining Walls

Saturation Effects on Initial Soil Liquefaction

Dynamic Soil and Water Pressures of Submerged Soils