Title

A constitutive elastic model for predicting seismic velocities of granular materials

Document Type

Conference Proceeding

Publication Date

7-29-2013

Abstract

Seismic velocity models of the near-subsurface (<30 m) better explain seismic velocities when all elements of total effective stress are considered, especially in materials with large cohesive and capillary pressures such as clays. Current constitutive elastic models that predict velocities in granular materials simplify the effect of total effective stress by equating it to net overburden stress, excluding interparticle stresses. A new proposed methodology calculates elastic moduli of granular matrices in near-surface environments by incorporating an updated definition of total effective stress into Hertz-Mindlin theory and calculates the elastic moduli of granular materials by extending Biot-Gassmann theory to include pressure effects induced by water saturation changes. At shallow depths, theoretically calculated seismic velocities decrease in clay and increase in sand with an increase in water saturation because interparticle stresses suppress the Biot-Gassmann effect. For standard sand and clay properties, net overburden stress be comes more influential than interparticle stresses at depths greater than 1 m in sand and 100 m in clay. In clays, the variation of seismic velocity with water saturation is almost double the range predicted when only net overburden stress is considered to influence stress at the grain contacts. The proposed model calculates seismic velocities that compare well with measured field velocities from the literature.

Publication Source (Journal or Book title)

26th Symposium on the Application of Geophysics to Engineering and Environmental Problems 2013, SAGEEP 2013

First Page

553

Last Page

565

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