A study on the influence of the plasticity index (PI) on the cyclic stress‐strain parameters of saturated soils needed for site‐response evaluations and seismic microzonation is presented. Ready‐to‐use charts are included, showing the effect of PI on the location of the modulus reduction curve G/Gmax versus cyclic shear strain γc, and on the material damping ratio λ versus γc curve. The charts are based on experimental data from 16 publications encompassing normally and overconsolidated clays (OCR=1-15), as well as sands. It is shown that PI is the main factor controlling G/Gmax and λ for a wide variety of soils; if for a given γc PI increases, G/Gmax rises and λ is reduced. Similar evidence is presented showing the influence of PI on the rate of modulus degradation with the number of cycles in normally consolidated clays. It is concluded that soils with higher plasticity tend to have a more linear cyclic stress‐strain response at small strains and to degrade less at larger γc than soils with a lower PI. ...

Effect of Soil Plasticity on Cyclic Response

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

Unified dynamic shear moduli and damping ratios of sand and clay

Use of liquefaction-induced features for paleoseismic analysis - An overview of how seismic liquefaction features can be distinguished from other features and how their regional distribution and properties of source sediment can be used to infer the location and strength of Holocene paleo-earthquakes

Two of the most important parameters in any dynamic analysis involving soils are the shear modulus and the damping ratio. Because both shear modulus and damping are strain dependent, curves must be developed to define their variation with shear strain. Fifteen studies (including this one) now provide results from tests on a wide variety of gravels. This paper combines the results of available investigations to develop best-fit relationships between (1) shear wave velocity and equivalent N60 from Becker penetration tests; (2) normalized shear modulus and shear strain; and (3) damping ratio and shear strain. The mean curve for the normalized shear modulus reported for gravelly soil in this study falls near the mean curve reported for sands by Seed and Idriss (1970). The normalized shear modulus curve is dependent on confining pressure, but essentially independent of sample disturbance, relative density, and gradation. The mean damping ratio curve falls toward the lower range of the data reported by Seed and...

Shear modulus and damping relationships for gravels

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

The results of cyclic loading tests on gravelly soils using a 12-in. diam triaxial test apparatus are described. The cyclic stresses required to cause —2.5% and —10% strain of saturated samples of gravelly soils are shown to be somewhat higher than those causing similar strains in sands. However, part of this increase may be due to the effects of membrane penetration and compliance in the test system. It is suggested that the superior field performance of gravelly soils over sands is probably due in large measure to the higher permeability of gravelly soils which will often permit sufficient drainage to occur to prevent the development of high pore-water pressures or liquefaction.

Robert T. Wong

Papers

Moduli and Damping Factors for Dynamic Analyses of Cohesionless Soils

Cyclic Loading Liquefaction of Gravelly Soils