LONG/WIDE DRILLED SHAFTS

[ANSIF]

Dear colleagues, regarding the construction of drilled shafts, often below water level, is there some kind of recommendation about the relationship between long/wide of the pile (L/B) that allows to minimize slenderness problems?

Thank you for your comments

 

[jdonville]

ANSIF,

Are you referring to the ratio of the length of the shaft to the diameter?

I would think that the slenderness ratio of the shaft would only come into play if the soils were too weak to provide lateral support, or if a significant portion of the shaft was extended into the "open" water.

I would think that in the latter case that the rules with respect to circular reinforced concrete columns would apply.

You may want to pose your question to a structural engineer.

Jeff


Jeffrey T. Donville, PE
TTL Associates, Inc.

http://www.ttlassoc.com

The views or opinions expressed by me are my own and do not necessarily reflect the views or opinions of my employer.

 

[ANSIF]

Jdonville, you are wrigth I mean length.

Thankyou for your comment.

 

[fndn]

As you're aware there are two capacities of a caisson-the geotechnical capacity and the structural capacity. The geotechnical capacity is considerably less than the structural capacity. The ground doesn't care about its structural capacity-all it know is that a caisson with a given geometry, skin friction and length is being installed. So whether your pile or "column" is short or not is not a concern, since the geotechnical capacity will govern.

 

[ANSIF]

I appreciate the comment.

Dear fndn, take into account the following scenario: it is projected a drilled shaft 40 m length with a diameter that can vary among 0.8 to 1.0 m. The reference area is located in the Mexican Pacific Ocean, in an area of high seismic risk. Don't you believe that an element like these may suffer problems in their seismic structural answer? Besides, since the constructive point of view, don't you think that it is possible to have serious problems in order to get an appropriate physical integrity of the element?.

 

[fndn]

ANSIF;

I hear you. I just wanted to point out that friction is a geotechnical concern and slenderness ratio is a structural capacity concern.

When we do seismic analysis in California, we're only concerned with the upper 16 m or so, unless the loads are very high in which case we have to resort to dynamic methods. In your scenario, it may be worthwhile to perform a load test and verify the ultimade load of a representative pile.