Allowable Movement

[Riggly]

I am analyzing some short drill shafts (using COM624). They are rigid, and the analysis shows that the tip is kicking off - there is no practically no flexure in the shaft.

Does anyone know of references, or know of some guidelines on the tolerable lateral movement of drill shaft under lateral loads? How much is too much movement? I normally embed the the shaft that there is practically no movement, but I think sometime the embedment might be too much.
(Apart from the tolerance set by the structural engineer etc how much should I be concerned about movement within the soil?)

Any thoughts?

 

[InDepth]

Typically geotechs will recommend limiting the tip deflection to 1/2 to 1 inch. NAVFAC and other documents discuss this.

 

[Riggly]

You may be referring to movement at the head of the drill shaft/pile. I am referring to lateral movement of the bottom tip. Bowles, 1995, 'Foundation Analysis and Design' said that displacement at the bottom in the direction of the load much over 1 or 2mm indicates that the analytical model may be inadequate or the lateral load is too large for the pier-soil system.

 

[jheidt2543]

Do you know you are actually getting movement? Do you have any of the piles instrumented? Or, is movement only indicated by your calculations and if so how much movement do you show?

 

[BigH]

You might want to scan through Poulos and Davis' book on Pile Foundation Analysis and Design - they have extensively covered laterally loaded piles - you might find something in there. It's been a while for me with laterally loaded piles; nothing jumped out at me. Tomlinson's Pile book might also have information. - but Jim made a good point - your movements - Analysis or Actual

 

[Riggly]

These movements were based on calculations. I expect movements, but I just wanted to know what's an ecceptable limit(if one exists). I was getting movement in the order of 1/3".

 

[BigH]

Doesn't seem out of line with examples in P&D.