Which pile type is best to use in overconsolidated silty clay?

[pacman49]

Which pile type is best to use in overconsolidated silty clay? example London clay?

Driven, Bored or CDA piles? (No water table is evident in tests)

 

[BigH]

I would prefer bored piles . . .

 

[dirtsqueezer]

Stone columns work too. Depends on how deep you need them to go. I think the idea is if you use a pipe or wood, they might deform with your hard clay.

 

[BigHarvey]

Agree with BigH

Regarding stone columns, their construction in this type of clay will require pre-drilling. The load capacity of a stone columns is about 25 tons, it might not be sufficient to replace piles even if you go for a raft.

 

[dirtsqueezer]

I think there's a matter of terminology with the stone columns. I've seen them pre-drilled or vibrated and injected. I was talking about the injected variety. But re-reading the post I don't actually know what London Clay is, so take that for what it's worth.

 

[BigHarvey]

Injected stone columns is, for me, a non-sense , since the way a stone column works is flexibility. The top of the stone column settles the same amount than the surrounding ground ( ie stress is distributed in relation with respective deformation moduli ). Grouting them makes it a bad pile and nothing else. This concept has been developed by specialized contractors ( and not the less famous ) to overcome lack of lateral strength in soft clays and peat which prevent the compaction of the stone backfill.

 

[dirtsqueezer]

I'm sure you have much more experience than me, as I've actually only seen one soil improvement project go in with that. I would, however, prefer that over the bored stone variety, as it would seem the injection process itself would lead to less settlement. Also, the stone they used was akin to railroad ballast that in my limited experience has little settlement. Not to cross your read on the situation. I'm sure augercast piles would be the very strongest.