Deformation parameters - Geotechnical Investigation and Design Tables - page 131

•

The table below is for a secant modulus at a Factor of safety of 2, ie 50% of the
peak strength.

•

The E u /C u value is dependent on the strain level.

•

For london clays (Jardine et al., 1985) found a E u /C u ratio of 1000 to 500 for
foundations but a larger ratio for retaining walls, when smaller strains apply.

11.15 Soil modulus from SPT values and plasticity index
•

These values correlate approximately with previous tables for large strain
applications.

•

This applies to rigid pavements.

•

Do not use for soft clays.

Table 11.15 Modulus values (Industrial Floors and Pavements
Guidelines, 1999).

Es/N Material

3.5 Sands, gravels and other cohesionless soils

2.5 Low PI (

<

12%)

1.5 Medium PI (12% PI 22%)

< <

1.0 High PI (22%

<

PI

<

32%)

0.5 Extremely high PI (PI 32%) >

11.16 Short and long term modulus
•

For granular materials the long term and short term strength and modulus values
are often considered similar. However for these materials there can still be minor
change between the long and short term state.

•

Short term Young's modulus E s = Long Term Modulus E l = β E s .

Table 11.16 Long term vs short term (Industrial Floors and
Pavements Guidelines, 1999).

Material β

0.9 Gravels

0.8 Sands

0.7 Silts, silty clays

0.6 Stiff clays

0.4 Soft clays

11.17 Poisson ratio in soils
•

A clay in an undrained state has a Poisson ratio of 0.5.

•

In the Odeometer test with negligible (near zero) lateral strain the Poisson ratio is
effectively 0.0.