PVD maximum spacing

[Canadaian]

Hi,

I am designing an embankment with preloading and PVD installation, we did define the critera at the end of preloading and we have a generous preloading period of 3 years it comes up that drains spacing to be 3 to 3.5 m depending on fill height.

Any one have an experience with PVD in such spacing ?
I know this spacing would work for sand drains very well and I worked with PVD in 1-1.8m spacing but not in the range of 3 m...any comments

thanks

CD

 

[BigH]

The question that begs to be asked is why you want a preloading time of 3 years? This is a long time for one-stage preloads and for ground to set idle. Does secondary consolidation have something to do about it?

In my experience, I have used pvd because the ground (very soft clayey soil) did not have sufficient strength to support the full height embankment. Hence, we put in pvd to be able to build the embankment up in stages. It was necessary to wait at 5 m height until we were able to attain an increase in the undrained shear strength to permit construction of the embankment to the next height. (spacing at 1.5m) As a result, the need for pvd was based on stability rather than settlement. What is your case? Can the soil support your height of embankment? If not, I would put the pvd a bit closer together and build in stages. If it can and it is only for settlement, then the spacing really is a reflection on how fast you want the settlement to take place. The downside of wider spacing is that if you overestimate the consolidation rate, then you might not "be done" at the three year period.