# 6 minute solutions- geotech problem 71



## terzaghi83 (Feb 5, 2012)

I have 2nd edition, 3rd printing of this book. there is no errata available but am stumped as to how they arrive at a the solution.

In my book, problem 71 states " A group of 30 in diameter caissons is constructed for support of a bridge. The group is arranged in a 3 by 4....."

If you have this problem please let me know if the solution makes sense. I'm trying to find out how the heck they say that it is 10 feet below the 2/3L distance to get to the midpoint of the clay layer.

Thanks.


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## chess5329 (Feb 5, 2012)

I don't have the book with me that I can check for the problem, but try to use the 2:1 method for a group of piles to see if works close to the answer.....I hope this helps.


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## terzaghi83 (Feb 7, 2012)

Yeah, they use the 2:1 method to obtain the DeltaP. My question is how they come up with the distance from the 2/3 point on the caisson group to the midpoint of the clay layer as 10 feet.


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