Deformation parameters - Geotechnical Investigation and Design Tables - page 123

11.2 Small strain shear modulus
•

The small strain shear modulus is significantly higher than at high strains.

•

The table provides small - strain typical values.

Table 11.2 Typical values of small - shear modulus (Sabatani et al., 2002).

Shear modulus, G Small - strain shear modulus G 0 (MPa)

Soft clays 3 to 15

Firm clays 7 to 35

Silty sands 30 to 140

Dense sands and gravels 70 to 350

•

For large strains G ls = E/2.5.

•

For small strains G ss = 2E = 5G ls .

11.3 Comparison of small to large strain modulus
•

The applicable modulus is dependent on the strain level.

•

The table provides the modulus values at small and large strains.

Table 11.3 Stiffness degradation range for various materials
(summarised from Heymann, 1998).

Strain level comparison Stiffness ratio

E 0 . 01 /E 0 0.8 to 0.9

E 0 . 1 /E 0 0.4 to 0.5

E 1 . 0 /E 0 0.1 to 0.2

•

Modulus at 0% strain = E 0 .

•

Modulus at 0.01% strain = E 0 . 01 (small strain).

•

Modulus at 1.0% strain = E 0 . 01 (large strain).

•

Materials tested were intact chalk, London clay and Bothkennar clay.

•

Figure 11.2 (from Sabatani et al., 2002) shows the types of tests appropriate at
various strain levels.

11.4 Strain levels for various applications
•

The modulus value below a pavement, is different from the modulus at a pile tip
even for the same material.

•

Different strain level produces different modulus values.

•

Jardine et al., (1986) found shear strain levels for excavations to be < 0.1% for

walls and as low as 0.01% if well restrained.

•

The modulus value for the design of a pavement is significantly different from the
modulus values used for the support of a flexible pipe in a trench.