Relationship between dry, drained and undrained young's modulus
Relationship between dry, drained and undrained young's modulus
(OP)
I'm a structural engineer recently converted to the dark side (geotechnical engineering). I understand there are drained, undrained and dry conditions for soil samples. Dry conditions mean no pore water exists and all the voids are filled with air. Drained conditions mean that pore water exists but the boundary conditions allow it to dissipate freely and thus no excess pore pressure exists. Undrained conditions mean that pore water exists and the boundary does not allow it to dissipate. This causes excess pore pressure to build up and modifies the soil's mechanical properties due to the presence of water.
Most numerical software allows for these three types of analysis, often providing several subtypes for the undrained case. I would like to understand better the material parameters to input in these programs. For instance:
- what relationships exists between undrained poisson's ratio and effective poisson's ratio
- what relationships exist between undrained young's modulus and effective young's modulus
- if the above relationships exist, are they dependent on the type of soil (sand, clay) and are empirical? OR can a general relationship be derived which is agnostic to soil type? If this general relationship exists what parameters are common to all soil types that it can use?
Most numerical software allows for these three types of analysis, often providing several subtypes for the undrained case. I would like to understand better the material parameters to input in these programs. For instance:
- what relationships exists between undrained poisson's ratio and effective poisson's ratio
- what relationships exist between undrained young's modulus and effective young's modulus
- if the above relationships exist, are they dependent on the type of soil (sand, clay) and are empirical? OR can a general relationship be derived which is agnostic to soil type? If this general relationship exists what parameters are common to all soil types that it can use?





RE: Relationship between dry, drained and undrained young's modulus
RE: Relationship between dry, drained and undrained young's modulus
I would also like to add that undrained and drained conditions also consider how the load is applied. Rapid loading is related to undrained conditions (short term loading), "slow" loading is related to drained conditions (long term loading).
For your question #1, you will see in Budhu's book extract, that for undrained conditions v=0.5, but this is because the classic theory of soil mechanics is based on saturated soils. So, if soil is undrained, then S=100% and therefore v=0.5. For drained conditions, typically 0.3~0.35 is considered.
RE: Relationship between dry, drained and undrained young's modulus
All of the discussed relationships will be empirical and therefore will be dependent on soil type.
RE: Relationship between dry, drained and undrained young's modulus
To me, soil modulus is the spring constant that is unrelated to dissipation of pore pressure. Consolidation characteristics are related to dissipation of pore pressure. So, in performing settlement calculations, if I'm below the preconsolidation pressure, I, "May" use soil modulus or I may use Cr.
Soil modulus is dependent on poisson's ratio.
Drained and undrained strength is a BIG factor in fine-grained soil strength. In the program I manage, I'd require both analyses to confirm that safety factors in slope or wall design considers both failure modes.
I'm no scholar. I'm just speaking from experience.
Good luck in your retooling from structural engineering. Geotechnical engineering seems more fun to me!
f-d
ípapß gordo ainÆt no madre flaca!
RE: Relationship between dry, drained and undrained young's modulus
RE: Relationship between dry, drained and undrained young's modulus
I'd be interested though! Doesn't yet make sense to me; however. . .
f-d
ípapß gordo ainÆt no madre flaca!
RE: Relationship between dry, drained and undrained young's modulus
RE: Relationship between dry, drained and undrained young's modulus
f-d
ípapß gordo ainÆt no madre flaca!