vertical sand drain material 3

[Canadaian]

Hi,

A Specification for vertical sand drain says that sand should be placed into holes as:

"Sand shall be placed to attain a relative density of 90 %".

Is it necessary to define this requirment?
How to ensure this requirment is achieved, what test?

thanks

CD

 

[dicksewerrat]

Are you wrapping the sand in a geotextile? to keep the sand and fines from mixing? Do they spec a gradation for the sand?

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[Canadaian]

Dicksewerrat

-it is vertical sand drain there is no wrapping at all.
- yes, there is gradation spec for backfill material.

 

[cvg]

relative density of 90% is quite high as we have used 70% in the past for sand filter drain. note this is "relative density" which is used for granular, non-cohesive material such as sand. The method can be found in the US Bureau of Reclamation - "Design of Small Dams". In the 3rd edition, it is on page 560.

 

[GeoPaveTraffic]

I agree with cvg that 90% relative density is high. That would be difficult to achieve in most, if not all, conditions. My assumption would be that the person righting the specification doesn't know/understand the difference between relative density specifications and Proctor specifications.

That point aside, how is anyone going to test a vertical sand drain? All but the very top is many feet below grade.

To you question is it necessary to specify a compaction in a vertical drain?, I have never seen it done. All that would likely be needed would be to compact the surface following installation of the drains and before construction of the remaining structure, which is probably already required as part of the site preparation.

 

[Canadaian]

cvg and GeoPaveTraffic

thank you for your comments.

-The vertical sand drains is to be installed 20m deep in firm becoming soft clay.

-the reason behind 90% relative density is to prevent any possible squeeze of clay inside the hole and ensure the column of sand is there in full section ...the gradation spec is 0-3% of fines and placement of sand to 90% relative density, should not impcat permeability...previous experince shows possible placement to this requirement for stone column material (more coarse material).

- measuring the mass of sand placed with known hole volume should provide information about relative density...determination is to follow ASTM D4253 and D4254.

Yet to look in the ref you gave cvg

thanks

CD

 

[BigH]

Installation of sand drains and stone columns are much different and you shouldn't think that because you achieved a certain value in the stone columns it is achievable for sand drains. How do you plan to achieve such a level of compaction or any specified level? Are you going to put in, say 150mm and then use a downhole tamper to achieve at least some modicum of compaction? Don't see any other way. I would suggest that if you are worried about squeeze, spec the hole a bit larger (you didn't say what diameter of sand drain - but say to use 150mm or 200mm - then fill it with concrete sand (see Ripley as quoted in Terzaghi Peck and Mesri).

 

[Canadaian]

Thanks BigH

-the hole to be used is 450mm, holes up to 300mm in dia had experienced clay squeeze in bottom.

-the plan is to use roding or jetting to achieve compaction.

- from yours and other reply it seems that 90% relative density requirement on high side...Any other figure beside 70% of cvg?

thanks

 

[looksatstars]

If you want to get 90% compaction on a uniform sand. I would use two concrete vibrators and drop about 2 foot lift of sand in with the vibrators and vibrate them out. that should easily get your 90% in a uniform sand.

 

[civilperson]

Relative density of clean sand of the order of 70% is equivalent to 90 - 95% compaction of Standard Proctor (D 698).

 

[cvg]

note that 70% "relative" is a common requirement by the bureau for building dams. As stated, that is equivalent to approx 95% standard proctor. IMHO anything more is difficult to achieve and unnecessary.

 

[Canadaian]

Thankk you cvg and civilperson.

CD