Consolidation required for drained conditions

[Spartacus89]

Hello Engineers,

I was wondering if anyone knows what consolidation is required to tend a clay from undrained to drained?

If I am doing any design (retaining walls, quays etc.) I would always check both conditions and I don't know if there is a way to not check both.

Books such as Craigs state that when dissipation is completed that the soil is considered drained. However, if I for example: -
1) create a bund which increased the total stress and the pore water pressure by 50kPa, then from odometer tests that will create a settlement of 100mm in 2.2 years
2) create a bund which increased the total stress and the pore water pressure by 200kPa, then from oedometer tests that will create a settlement of 142mm in 1.7 years

In both of these examples dissipation has occurred, otherwise the soil would not consolidate, but neither do I believe that they have tended from undrained to drained.

If anyone can give me some guidance, even if it's that I need to check both cases and let the Professors worry aboutwhat is required for it to change.

Cheers
D

 

[geotechguy1]

Drained loading: Load is applied slowly relative to the rate that water is squeezed out of the soil (no excess pore pressure)
Undrained loading: Load is applied fast relative to the rate that water is squeezed out of the soil (excess pore pressure is generated)

In the long term an engineering structure will end up drained so in reality you should check both.

 

[EireChch]

Its not about the magnitude of settlement its got to do with your drainage length and Cv (coefficient of consolidation). From this you can estimate the time take to reach 95% degree of consolidation which is typically taken as full consolidation has occurred.

Also, I wouldnt be attempting to use any method to negate the need to do both a total and effective stress analysis.

 

[Spartacus89]

geotechguy1/EireChch,

Thanks for the replies.

D

 

[fattdad]

There are two conditions - consolidation and drainage under shear. Don't confuse these conditions.

If you place an embankment fill and give it a lot of time, the pore pressures will dissipate. We call that consolidation.

If you have a consolidated layer and it's subjected to shear quickly, the pore pressures don't have sufficient time to dissipate as the shear is applied and that's undrained strength.

If the soil has favorable permeability (or Mv, Cv), then it becomes moot.

Knowing the difference is where the matter lies.

f-d

ípapß gordo ainÆt no madre flaca!