what you test????????

-the testing apparatus; oedometer

-the standard of primary consolidation is known: according to the French standard XP P 94-090-1, bearings maintained 24 hours . 

But for secondary consolidation; I have absolutely no idea. , neither on  duration of the test nor PROCEDURE method

The following ASTM code gives procedure for evaluating primary as well as secondary compression in soils using oedometer test.

ASTM D2435 / D2435M 

Standard Test Methods for One-Dimensional Consolidation Properties of Soils Using Incremental Loading

I thank Madhavi Latha Gali  passage for her help.

I have not found  PROCEDURE method and duration of the test  for secondary consolidation in   (ASTM D2435 ) 

To determine  settlement  we need to find  index  primary and secondary compression . the curve  compressibility gives index primary compression and curve consolidation gives index secondary compression, The question that arises is this:

What Incremental Loading  (which gives   index secondary compression) to be taken in calculating settlement ?

To get secondary compression one just maintain the load AFTER completion of primary consolidation and then and get a e-log(t) curve.  The whole idea of load duration is not relevant because secondary compression/consolidation is NOT a consolidation process!!  Thats why some researchers (like myself) call it secondary compression, NOT secondary consolidation.

The catch is: the coefficient of secondary consolidation is DEPENDENT on magnitude of stress.  In fact, even  for a give stress, its actually changing slowly with time (& u will see this clearly if u allow the test enough duration, say 30 days. These are supported by publications in respectable venues.

To make life even more tricky, the time when secondary compression starts depends on thickness of soil.  Its not a material property.  

Thank you very much for your answer  and explanation  S-C. R. Lo . 

I have another question about ;

if there is   analytical  formula to estimate   the coefficient of secondary consolidation not to rely only on the  standard statistical Method  such that the multiple and simple regression  ???

Even i am working with creep for some period of time. if it is a problematic soil(soft, organic), let it be loaded untill you have time and apparatus according to all your planning. More the time, it may give you some interesting results. but the same doesnt go for the regular soils.

The secondary compresion is conected with C(alpha) , t - time ( t1=time after primery consolidation, t2=time that you woluld like to check this settelemts), H= thickness of layer, and e0. In your calculation you will take into account the C(alpha) for pressure that will be generated by your construction.     

Check document ISO/TS 17892-5:2004Incremental loading oedometer test

As stated above ,carry out the standard consolidation test.Plot e vs log t. Get c(alpha).You can then calculate secondary consolidation settlement. 

Dear Mohammed el amin Bourouis , It's a very late response but I hope it could be useful for you and others. Following the likes provided you will find sufficient information on Creep Test on Soil and Soil-TDA mixtures. https://doi.org/10.1007/s40098-019-00407-0

Article Laboratory Creep Parameter Determination of Sand–TDA Mixture...

Raghad Mouhamad Madhavi Latha Gali S-C. R. Lo Vikas Gingine Norbert Kurek Nabil Ismael