Geoscience Reference
In-Depth Information
Deformation parameters
11.1 Modulus definitions
•
The stiffness of a soil or rock is determined by its modulus value. The modulus is
the ratio of the stress versus strain at a particular point or area under consideration.
•
Materials with the same strength can have different stiffness values.
•
The applicable modulus is dependent on the strain range under consideration.
•
The long term and short term modulus is significantly different for fine grained
soils, but slightly different for granular soils. The latter is considered approxi-
mately similar for all practical purposed.
•
Additional modulus correlations with respect to roads are provided in Chapter 13
for subgrades and pavements.
- Modulus usually derived from strength correlations. The 2 most common are:
Secant modulus is usually quoted type for soil - structure interaction
models.
Resilient modulus applies for roads.
Table 11.1
Modulus definitions.
Modulus type
Definition
Strain
Comment
Initial tangent
Slope of initial
Low
Due to closure in micro-cracks from sampling
modulus
stress concave line
relief (laboratory) or existing
discontinuities (in-situ).
Elastic tangent
Slope of linear
Medium
Also elastic modulus. Can be any specified
modulus
point (near linear)
on the stress strain curve, but usually
at a specified stress levels such as 50% of
maximum or peak stress.
Deformation
Slope of line between
Medium
Also secant modulus.
modulus
zero and maximum
to high
or peak stress
Constrained
Slope of line
High
This is not mentioned in the literature. But
modulus
between zero and
values are lower than a secant modulus, and
constant volume
it is obtained from odeometer tests where
stress
the sample is prevented from failure, therefore
sample has been take to a higher strain level.
Recovery
Slope of unload line
High
Insitu tests seldom stressed to failure, and unload
modulus
line does not necessarily mean peak stress has
been reached. Usually concave in shape.
(
Continued
)
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