vertical pile load test by anchor method

[Balageotech]

Dear Geotechncial engineers,

I am plannning to coduct a pile load test , what is the suitable method? Kentledge with surcharge load or anchor pile method?
What are the advantages and disadvantages in using anchor method for vertical pile load tes?

Is there any techncial concern on using anchor method than sucharge load methos?

Regards
Balageotech

 

[Ron]

ASTM D1143 - "Standard Test Methods for Deep Foundations Under Static Axial Compressive Load" is one common way of performing static load tests on piles.

If your pile has a very low design capacity, then using a dead load reaction (as you are calling "surcharge") can be done, keeping in mind that your dead load will have to be more than twice the design capacity of the pile since the load test should be done to twice the design capacity.

As your pile design capacity increase, using a dead load reaction system becomes increasingly difficult unless you have some very heavy equipment or other dead load reaction material that can be left in place for the entire length of the test and rebound.

Using reaction piles for the test usually works out better, but can be more expensive, since you'll be placing at least 2 reaction piles, (likely 4) so as to obtain adequate reaction for the test pile without failing the reaction piles in tension. Depending on soil conditions, a pile reaction system might not work because it depends on skin friction for its primary resistance.

 

[oldestguy]

Using the anchor piles for reaction for a friction (mainly) test pile, be aware that the proximity of the anchors to the test pile can have some bearing on the true support capability of the test pile. For instance compaction caused by displacement anchor piles near the test pile may occur and affect the validity of the test results. Spacing of the piles.

On the other hand using a dead-load as a reaction, does placing that load nearby compact the soil as a form of surcharge and also affect results of a friction pile?

 

[Ron]

OG...good points. Generally, we like to keep the spacing of reaction piles to about 6x the pile diameter. As for dead load, spread the supports apart as much as possible, preferably beyond the 6x consideration.

 

[PEinc]

ASTM D 1143/D 1143M-07, Standard Test Methods for Deep Foundations Under Static Axial Compressive Load, requires a clear distance between the test pile and any anchor piles of 5 x pile diameter or 1.5m (8 feet) minimum. For timber cribbing supporting the jacking frame, the requirement for clear distance is 1.5m (5 feet) minimum. These minimum distances dictate to which production piles you can attach your testing frame and, therefore, are used to determine the size of your jacking beams. If you do not or cannot use production piles as tension reaction piles, you can also use tiedown anchors, which also must meet the minimum clear distance requirement.

http://www.PeirceEngineering.com

 

[oldestguy]

I see I lost some of my text. I'd add a few things. Don''t depend on one method to measure pile movement. Crawling around in these locations someone can trip on the devices and throw off the readings.. In addition to dial gages and a substantial off-set support for them, I add a taught piano wire strung through the site, laid against the pile or other attachment with ruler there.. Also set up a transit-level off to the side for an occasional reading. Remember sun shining on things can change dimensions, so shade protection is needed. How long ago was the jack calibrated? When you are down in a hole can you meet the off-set requirements of ASTM?