Is there any relationship between pile dia versus max. allowable pile length? 2

[NewbieInSE]

Hello,

Often my seniors seem to say don't use a 20-inch diameter pile for a length higher than 100 feet or so. I couldn't get the proper reasoning behind it.

If a 20-inch or 18-inch pile needs to be laid at a 120 feet depth to reach the hard layer and if the concerned pile has the structural capacity to bear the axial load along with bending moment then wouldn't it be enough?

I would like to know your opinion.

Thanks.

 

[skeletron]

That ROT is probably related to slenderness kL/r < 200.
You could also consider the construction of it depending on the type of pile. The deeper the hole, the harder to maintain a narrow profile (re: tolerance etc).

 

[SlideRuleEra]

Is there any relationship between pile diameter versus max. allowable pile length?

Not really, but this does not mean your seniors are wrong. They are probably restricting their advice to the point-bearing pile in the area where you practice.

Many engineers consider piles to be either strictly "structural" or, alternatively, "geotechnical". In reality, piles are both at the same time.
Point-bearing piles thru water or very soft soil tend to be more "structural" (think columns).
Friction piles are more "geotechnical" (dependent on soil properties).
Of course there can be any combination of "structural" and "geotechnical".

Don't take my word for this, read "Bethlehem Steel H-Piles, particularly Section 5 (Lateral Support for Long Piles in Soft Soil) and Section 6 (Determining Unbraced Length).

Note: This book is obviously for steel piles, but the same laws of physics / engineering principles apply to concrete and wood piles.

 

[NewbieInSE]

Thank you SLideRuleEra. I'll look into it.