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Wick drains and Stone Columns Reference 3
- Thread starter pelelo
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There are several methods for dissipating pore pressures in clayey/ silty soils: stone columns and wick drains are 2 of the most popular.
I just want to educate myself using both technologies and understanding the differences, advantages and disadvantages.
This is for a potential project that will involve the construction of a highway on soft clays and the plan is to pre-load and install either of these technologies to accelerate consolidation.
I just want to educate myself using both technologies and understanding the differences, advantages and disadvantages.
This is for a potential project that will involve the construction of a highway on soft clays and the plan is to pre-load and install either of these technologies to accelerate consolidation.
Pelelo - I'll look up some references for you in a few days - we used for the Calcutta clay plains pvd wick drains at 1.5 m spacing for purposes of speeding up consolidation during stage loading (not preloading) - worked well when other issues didn't raise their head (political pressure for example. The improved layer (increase in Su due to the consolidation) supported 11 m high RE MSE walls - underwent up to 1100 mm of settlement during the construction period.
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Thanks a lot BigH.
For accelerating the consolidation in embankments, do you think there is any advantage or disadvantage between using wick drains vs Stone columns? or do they both do the same?.
From what i can see, wick drains are more simple to use and from the construction point of view they seem to involve less production than stone columns.
For accelerating the consolidation in embankments, do you think there is any advantage or disadvantage between using wick drains vs Stone columns? or do they both do the same?.
From what i can see, wick drains are more simple to use and from the construction point of view they seem to involve less production than stone columns.
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Pelelo, my view:
Wick drains can go in very quickly. They get "shoved" in, cut off and the machine moves to the next location - typically 1.5 m away - the purpose of the drains is to reduce the porewater pressure relief path. Wick drains have overtaken the older form of relief which was sand drains.
Stone columns also do the same thing - but if the purpose is to speed consolidation, then the porewater pressure relief path will have to be of the same order - 1.5 m . . . or else what is the purpose. Now, if the stone columns are also used to put in stiff inclusions into the soil for increased bearing under footings or a mat - that is a different story.
So - the bottom line - if the purpose is solely to speed up consolidation, then wick drains, in my view, is the way to go. If the purpose is to reinforce the stratum's stiffness, then it is the stone columns that would be used - more for the stiffness than the consolidation purpose as the stone columns would be more widely spaced.
Some references on wick drains. I do have more but have to get to the hard drive that I have stored it in . . . :
- note that the "upper exposed part" of the wick drain falls over to near horizontal. A funny thing in India, the client made a statement when he saw this - "I thought that the wick drains are vertical." Funny.
Wick drains can go in very quickly. They get "shoved" in, cut off and the machine moves to the next location - typically 1.5 m away - the purpose of the drains is to reduce the porewater pressure relief path. Wick drains have overtaken the older form of relief which was sand drains.
Stone columns also do the same thing - but if the purpose is to speed consolidation, then the porewater pressure relief path will have to be of the same order - 1.5 m . . . or else what is the purpose. Now, if the stone columns are also used to put in stiff inclusions into the soil for increased bearing under footings or a mat - that is a different story.
So - the bottom line - if the purpose is solely to speed up consolidation, then wick drains, in my view, is the way to go. If the purpose is to reinforce the stratum's stiffness, then it is the stone columns that would be used - more for the stiffness than the consolidation purpose as the stone columns would be more widely spaced.
Some references on wick drains. I do have more but have to get to the hard drive that I have stored it in . . . :
- note that the "upper exposed part" of the wick drain falls over to near horizontal. A funny thing in India, the client made a statement when he saw this - "I thought that the wick drains are vertical." Funny.
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