AK92
Geotechnical
- Aug 20, 2013
- 45
Hi all,
I'm calculating post-PVD secondary consolidation for a soil that is going to be improved using prefabricated vertical drains. Now the secondary consolidation equation goes like this: s = Ca/(1+e0) X log (t2/t1). The log (t2/t1) is bothering me a lot now, because I am using prefabricated vertical drains to accelerate the consolidation, it doesn't make sense that I would have significantly more secondary consolidation settlements just because I decreased the time period required for primary consolidation.
The equation implies that the settlement is heavily dependent on t1 (the time at the end of primary consolidation). For example for a time period of 100 years:
t1 = 4 years, t2 = 100 + 4 = 104 years, log(t2/t1) = log(104/4) = 1.42
t1 = 50 years,t2 = 100 + 50 = 150 years, log(t2/t1) = log(150/50)= 0.48
This is a difference in settlement prediction of a factor of 3!
Now I don't have that much experience but I think that the secondary consolidation settlement shouldn't depend on t1 at all. If the equation was log(t2-t1) instead of log(t2/t1) it would make a lot more sense.
Now another thing is that: If the soil is in an overconsolidated state during the working load, is it OK to ignore secondary consolidation and just use recompression settlements to calculate the residual settlement? My site is made mostly of marine clay with some limited areas where organic clays are present.
Thanks!
I'm calculating post-PVD secondary consolidation for a soil that is going to be improved using prefabricated vertical drains. Now the secondary consolidation equation goes like this: s = Ca/(1+e0) X log (t2/t1). The log (t2/t1) is bothering me a lot now, because I am using prefabricated vertical drains to accelerate the consolidation, it doesn't make sense that I would have significantly more secondary consolidation settlements just because I decreased the time period required for primary consolidation.
The equation implies that the settlement is heavily dependent on t1 (the time at the end of primary consolidation). For example for a time period of 100 years:
t1 = 4 years, t2 = 100 + 4 = 104 years, log(t2/t1) = log(104/4) = 1.42
t1 = 50 years,t2 = 100 + 50 = 150 years, log(t2/t1) = log(150/50)= 0.48
This is a difference in settlement prediction of a factor of 3!
Now I don't have that much experience but I think that the secondary consolidation settlement shouldn't depend on t1 at all. If the equation was log(t2-t1) instead of log(t2/t1) it would make a lot more sense.
Now another thing is that: If the soil is in an overconsolidated state during the working load, is it OK to ignore secondary consolidation and just use recompression settlements to calculate the residual settlement? My site is made mostly of marine clay with some limited areas where organic clays are present.
Thanks!