Drilled Caisson Load Test Required?

[SrVaro]

We are having a debate if per code (IBC 2009, with the older codes similar), drilled cast-in-place concrete caisson are required to be load tested. The design compressive load on the drilled caissons will be on the order of 600TON, thus a load test would have to be for at least two times this value, equalling 2,400kip. Note there is no net uplift and lateral load is not a concern for this discussion.

FYI, A geotech investigation has been completed and they recommend a skin friction of 3TON/ft2 for a length within competent rock. Their report mainly mentions integral testing of the caissons to verify proper construction, but not load testing.

To me it seems as if the code is unclear as to if a load test is required on the caissons. For example, section 1810.3.3 says "the allowable axial and lateral loads on deep foundation elements shall be determined by the approved formula, load tests, or method of analysis". Thus an option but not required. However, section 1810.3.3.1.1, states that a load test is required for a driven pile with a capacity of greater than 40TON, but no mention of a drilled caisson. There are additional sections that mention load tests but negate it with a statement if the design is based on a geotech investigation.

I have searched for older threads, but none seemed to specifically address the question of "does a drilled caisson loaded greater than 40TON require a load test?". (Sorry in advance if I did miss one!) I am starting to convince myself a load test is not required, but was interested in others opinions.

Thank you.

 

[JAE]

I've specified hundreds of drilled piers and never required a load test - but I didn't ever specify a 600 ton pier either...that's a lot of load. Not sure if you could create that much test load anyway.

 

[Teguci]

Is your foundation a pile or a pier? (and yes, IBC provides the definition). If you have a pile, then you should provide a load test (good luck!) For a pier, a geotech report and a downhole inspection is usually required but thats it.

The FHWA has several publications that you can get for free from them regarding testing and safety factors to be used for deep foundations (piles and piers) without testing, but their use will have to go through the building official's acceptance.

 

[graybeach]

Projects I've been involved with with this magnitude of drilled shafts have had Osterberg load cell testing. You can google and find a lot of info about this.

 

[wiktor]

The intention of the physical test is verification of the actual pile capacity. For a typical drilled friction pile it definitely a must.
For a wide pile drilled and socketed into the rock (BTW, what's the end bearing capacity?) that's definitely not required.

 

[hawkaz]

As others have stated- I'm not aware of any specific requirement, however if there are any doubts, a load test may help uncover issues while they can still be easily addressed. With the magnitude of loading you have- it may be advisable to suggest this to the owner and contractor.

I'm testing my memory- but I believe the John Hancock building in Chicago was 30-40 floors up when they started having settlement issues at some caissons. My understanding is that the soil at the caisson walls collapsed as they were placing concrete and pulling the casing, but nobody noticed. Once they started getting significant loading, excessive settlement was identified. The repair was difficult since so much framing was already in place.

 

[dcarr82775]

Never seen one done on a drilled pier, and I do not think the code requires one. As Teguci pointed out, piers do not require testing. The only time I have seen it done beforehand is when there were hundreds of drilled piers and tests had the potential to drastically lessen their lengths (cost savings).

 

[SrVaro]

Thank you for the responses.

JAE- I have never specified a load test for a drilled caisson before, but am getting some push back on this project. This is for a material storage silo.

Teguci - It is a drilled shaft per the definitions of section 1802. Within IBC 2009, a pile is usually associated with a driven member. Thus, some of the "confusion". As stated within the post a geotech investigation has been completed. And of course, construction inspection will be required during drilling, placement, etc of the drilled caissons.

graybeach- If a load test is required the Osterberg is the direction we are looking at as I do not want to add additional caissons for the anchoring of the load test. The contractor we are working with is estimating the two would cost roughly the same.

wiktor- The caisson is expected to be 4' diameter, thus "wide" in my opinion. The geotech is recommending not using the end bearing, only skin friction. This is why none was listed within the post, should have mentioned that. Not sure why we are not using end bearing, but even at 10ksf it would only be approximately a quarter of the required capacity.

hawkaz- The owner and contractor are debating the need for the load test, thus why I have been requested to research if it is required per code. In discussions with the geotech, there is not a concerns as to their specified capacities providing they are designed and constructed properly.

dcarr82775- Unfortunately the schedule will not allow for a redesign once the load test is completed. But I agree if one could be completed, it would allow for a possible reduction of drilled depth.