Angluar Pile Group Action

[someengineer]

Hello,

I am designing a small foundation for a cellular tower using micropiles.

Due to limitations in equipment, we need to use 2-150 dia (grout) vertical piles that would be side by side (150mm center to center spacing). Does anyone know a reduction factor for skin friction resistance if we went with this system? The piles are going into bedrock (if we hit it) or possibly a conglomertate type material.

We were also thinking that we may need to angle the piles slightly to prevent any group action. The piles need to go down about 7m each if we hit bedrock and 12.5m if its conglomerate. If we went with angular piles, does anyone know what approximate distance the toe of the piles should be apart?

Anyways hope this makes sense!

Thanks!

 

[someengineer]

A side note:

I am familiar with the Converse-LaBarre formula, and with this system, the formula dictates an efficiency of 75%. Does anyone agree with this assesment? I think it sounds reasonable.

 

[swearingen]

If you compare the perimeter of the piles themselves to the perimeter of a 1/2 pile, a straight section of 150mm soil between them, and then another 1/2 pile, you get 771mm vs. 942mm respectively. This gives an efficiency of 82% - so, yes, it looks like it's in the ball park...

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^ supposed to be circles...


If you "heard" it on the internet, it's guilty until proven innocent. - DCS

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[msquared48]

I trust that you are using more than two piles to support this cell tower...



Mike McCann
MMC Engineering

 

[someengineer]

haha yes, theres 3 piles per leg, 2 vertical and a batter pile. 9 piles in total. we're pretty confident that this will work just fine and we'll be proof testing every pile to ensure this.