within the range of strain amplitude specified. This assumption is usually made in most

soil dynamics analyses because of the low-vibration amplitudes involved. If the cyclic

hysteresis loops are obtained from triaxial test specimens, the resulting modulus will be

the stress-strain modulus, E. If the tests involve simple shear or torsion shear such that

modulus will be the shear modulus, G. In either case, the same equations apply.

The shear modulus, G, can be computed from the stress strain modulus

and Poisson's ratio as follows:

(12-21)

E

G=

2(1 + )

The shear strain amplitude, Ae, may be computed from the axial strain amplitude, e, and

Poisson's ratio as follows:

(12-22)

Ae = *ε*(1 + )

For the special case of saturated soils, Poisson's ratio is

0.5, which leads to the following:

G = E/3

Ae = 1.5*ε*

12-18

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