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Guys, I need an immediate answer

Guys, I need an immediate answer

(OP)
Guys,

Can you please calculate or model for me following case.

Cantilever bored pile. Depth of excavation is 6m, depth of pile is 12m. Cohesion of the material is 25 kpa, internal friction angle is 22. E=90.000 kPa. Pile is 65cm in diameter and tangent which means spacing is 65cm too.

Please assume interface is 1.0, no reduction in interface. Also please include a 120 kN/m2 surcharge at the 0 level (pile level) 0.5m right to pile head.

I have calculated maximum bending moment around 180 kNM/m which is around 120kNm per pile. What is your result?

RE: Guys, I need an immediate answer

Without any calculations, it would appear to me that even if this was a solid wall that it is likely to fail.

RE: Guys, I need an immediate answer

(OP)
Really?

Tangent piles with 65cm diameter. 6m embedment length. Most calculations I have performed showed that moment is around 180kNm and displacement around 1.5cm?

RE: Guys, I need an immediate answer

IMHO, oldestguy is probably right. Success or failure will be a close call. A 1930's rule-of-thumb for a cantilever wall is that embedment should be approximately equal unsupported projection, which it is... but that rough assumption is without a surcharge.

RE: Guys, I need an immediate answer

I usually get 1.1 to 1.2 times the supported soil for the embedment, and that is considering arch action of the soil.

Mike McCann, PE, SE (WA)

RE: Guys, I need an immediate answer

The "immmediate answer" part is what struck me. You are off on the wrong foot.

RE: Guys, I need an immediate answer

(OP)
What I have noticed is given below:

If we model that 120 kN/m2 with a raft (in my case, it is true, it is a building load) approximate bending moment on pile is 300 kNm/m
If we do not model the surcharge with raft and directly apply load to soil, bending moment increase 2 times!!

This is very important. I think, if it is a building, I should apply it with raft.

RE: Guys, I need an immediate answer

bdbd,

This is a discussion site. We do not do your calculations for you or check them, immediately or otherwise. You have not said what method you are using to calculate the moments or determine the depth of the pile below ground. That is the sort of thing we discuss!

Yes, adding a Raft and tying it into the top of the piles will affect the result if it is providing horizontal restraint. You will essentially have a propped cantilever instead of a cantilever pile. It will also affect the depth required for the piles as it will reduce the horizontal thrust at the bottom.

But then you have to consider settlement. How much is the soil under the raft expected to settle over the long term. What are the piles founding in. How far will they settle?

if there is a big difference you will need to look at differential settlement problems. And we know nothing of the overall structure above. Is there other structure loading directly onto the piles?

RE: Guys, I need an immediate answer

(OP)
Rapt,

Thank you. I have solved the problem. The 120 kN/m2 is a building. It is not providing lateral support to the piles by a connection.

But, if I model the building above with a raft it will reduce the bending moments on the pile. This is my discovery for today.

RE: Guys, I need an immediate answer

Keep discovering...you'll amaze yourself.

RE: Guys, I need an immediate answer

I am intrigued. How does modelling the loading on the soil as a Raft make the moments in the piles any different to modelling it as a loading corresponding to the raft load? Unless there is a connection between the raft and the piles?

RE: Guys, I need an immediate answer

Ron, that one made me laugh.

Also - I have completed my calculations immediately, as requested, and will give them to you after you send me my fee. ;)

"It is imperative Cunth doesn't get his hands on those codes."

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