## Time period from undrained to drained

## Time period from undrained to drained

(OP)

In slope stability analyses, we generally use drained parameters (c', phi) for long term assessment of slopes and undrained parameters (Su) for short term assessment.

After how many days/weeks/months/years does a material go to a "drained" conditions.

let's assume for this question that we have clayey SILT and it is a cut slope (as opposed to a a fill embankment). Also, i am just dealing with static conditions (no seismic). Am using limit equilibrium method to calculate a factor of safety.

After how many days/weeks/months/years does a material go to a "drained" conditions.

let's assume for this question that we have clayey SILT and it is a cut slope (as opposed to a a fill embankment). Also, i am just dealing with static conditions (no seismic). Am using limit equilibrium method to calculate a factor of safety.

## RE: Time period from undrained to drained

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## RE: Time period from undrained to drained

A practical measure of this time is t99, the time required to achieve 99% of the equilibrium volume change, which for practical purposes, we consider to be equilibrium. Using Terzaghiâ€™s theory of consolidation, we can estimate the value of t99:t99=4*(D^2)/Cv

where t99 is the time required for 99% of the equilibrium volume change, D the greatest distance that water must travel to flow out of the soil mass (length units), and Cv the coefficient of consolidation (length squared per unit of time).

Do you have the properties of the silt?

## RE: Time period from undrained to drained

## RE: Time period from undrained to drained

I have never heard the t99 idea for estimating the time to get to drained. that is a good idea. Stoyan - can you provide some more details on the reference please?