Piles in Rubble Fill 1

[geojosh84]

Hello all,

I am currently working on a project that a large portion of the site falls within the footprint of an arena that was partially below grade to depths of approximately 40 feet.

The arena structure was reinforced/post tension concrete that was imploded and the removal of the debris is unknown. We do know the bleachers/finishes we removed and the interior was partially back filled without compaction. As of now we are completing electromagnetic and resistivity surveys to try to delineate buried debris along with hsa and air track borings. Preliminary borings do confirm shallow refusals around 30' below grade in this area of the site.

A few of the structures planned for development in this area will require deep foundations to support the proposed loads. Based on experience in this area, piles will need to penetrate beyond the rubble depth to achieve capacity.

I wanted to see if any one had any experience with deep foundations penetrating through reinforced concrete rubble.

As of now we are leaning towards predrilled holes utilizing an airtrack rig then recommending auger cast piles or belled caissons. Another thought was micropiles. I am not looking for design recommendations, just anyone with past experience with pile construction in "similar" subsurface conditions.

Happy holidays and a happy new year.

Thanks in advance

J

 

[MTNClimber]

In my experience these situations are very problematic and costly for the owner. Usually micropiles are the best option since it's relatively easy to change drilling techniques and bit types. You may not be able to drill through the obstructions using drilled shafts. I don't have enough experience with augercast piles in these situations but I have a feeling that they may refuse too but hopefully someone else can provide some real insight on this.

The piles should extend past the rubble and the geotechnical axial resistance should be ignored for the portion in the rubble debris. Regardless of which pile type you use, make sure the owner and contractor are well aware that the debris will likely cause schedule delays and cost can vary significantly depending on how difficult it is to drill through the obstructions. Test pits may be helpful for the contractors bidding the work so they have a better visual of what they will be drilling through. It will also help you figure out if you need to leave the upper portion cased. If the rubble has large voids you will likely lose your grout without permanent casing.

 

[BridgeSmith]

We've driven steel H-piles successfully through alluvial fills with cobbles and boulders and occasionally through thin concrete spread footings. Unless the concrete rubble is in large pieces or is heavily reinforced, 14" H-piles with pile points attached should drive through with getting deflected too much.

 

[MTNClimber]

If driven piles are going to be used, I would opt for a vibratory hammer so you can extract the pile if refusal is encountered or if the piles start to drive out of alignment. I've had several HP14x89 steel piles driven with a large hydraulic impact hammer refuse or kicked out of alignment pretty easily on a site with 10 to 20' of urban fill containing demolition debris. Some of the piles that kicked out of alignment were so badly bent that they had to be extracted in 15' segments and cut before continuing with the other segments. The piles ended up being shaped like a J or a U.

 

[geojosh84]

MTN/hotrod, thanks for the response. We are thinking that predrilled boreholes with casing advanced using an airtrack rig may be the better bet.

I wouldn't be as concerned with driving in alluvial deposits with cobble. The reinforcement in the concrete has us weary of giving driven piles as a recommendation, seems like MTN has experienced what we're trying to avoid.

 

[MTNClimber]

Here are some photos of them removing one of those piles. I remember there was only 10' of urban fill in that area. Couldn't imagine what 40' would of done.

 

[BridgeSmith]

We've had a few piles that bent into U shape also, MTNClimber. Usually, it was because it hit a large boulder. The feasibility of driven steel piles would seem to be dependent on the size of the rubble - 1' - 2' diameter is probably ok, but if it's bigger than that, there could be trouble.

On the other side, we've had difficulty with augers that are anything less than twice the diameter of the cobbles, so if the rubble is more than 8", predrilling may create more problems than it solves.

I don't know how using a vibratory hammer would be different. We've never used one for H piles - just sheet piling. For sheet piling, a diesel hammer will drive it deeper in dense material than the vibratory. Our Geology guys tell us driving with a vibratory, expect refusal where their SPT goes over 40 blows per foot, but the diesel hammer will get us to where the SPT is around 60 blows per foot.

 

[BridgeSmith]

I wouldn't worry about reinforcing steel with H piles - it'll slice right through it, especially if you're using a diesel hammer. I'd be more concerned with the bars getting wrapped around the auger bit and binding it up. You could end up pulling the auger and trying to remove the steel bars wrapped around it. way more often than you care to.

 

[MTNClimber]

I don't know how using a vibratory hammer would be different.

My experience with the vibratory hammer was when an obstruction was encountered the contractor could pull the pile back up and either try again or find the next closest location. The piles were rarely damaged with the vibratory hammer but, as mentioned before, several piles were damaged with an impact hammer. All piles that were vibrated down were proven with an impact hammer or left hanging and then driven to completion. I remember the piles being vibrated down into weathered shale with blow counts above 100. But you can see in the photo that it was a big hammer with full metal jacket.

 

[BridgeSmith]

MTNClimber, I'm sorry, I just reread my post and realized I wasn't clear that the blow counts of 40 and 60 were for sheet piling, not H piles. It would not surprise me at all that you could drive H piles in much harder material.

 

[geojosh84]

I'm not convinced that driving H sections would be feasible at this site. Regardless, I appreciate the suggestion hotrod. MTN, those are some good photos, thank you.

Do either of y'all have experience using air rotary?

 

[BridgeSmith]

The feasibility of driving H piles depends on whether the pieces of concrete are large enough to deflect the piles, and if the pieces are that large, do you have the flexibility to move over a few feet and try again.

Even #8 or #9 rebar that is loose, or connecting broken pieces of concrete, is of no consequence to a driven H pile with a driving tip on it. If the pile hit a #11 or #14 rebar, that would slow it down, or possibly stop it.

 

[BridgeSmith]

If there's much rebar in the rubble and they're going to use an auger, they'll need to keep a cutting torch handy to cut the bars that will inevitably end up tangled around the auger.

 

[geojosh84]

This was a very large structure in its hay day, pre-implosion so I am assuming rubble debris is on the larger side.

I don't think there will be much augering with an airtrack.

 

[geojosh84]

Just for reference, here is a photo of the old structure during construction.

 

[SlideRuleEra]

...pre-implosion so I am assuming rubble debris is on the larger side.
I don't think there will be much augering with an airtrack.

The arena in the photo was imploded with a total of 400 pounds of explosives, unless large debris was removed after implosion, expect sizable pieces of reinforced concrete.

IMHO, MTNClimber has outlined the best way to proceed: heavy HP, driven (and extracted as needed) with a vibratory hammer. Each HP is a probe used to find a reasonably clear path through the rubble... if you are very lucky, enough of the HP will penetrate the rubble field to provide foundation support. Of course, the foundation design will have to accommodate piling located at seemingly random locations. Doubt that an Ingersoll-Rand Air Track pneumatic rotary drill will be successful placing piling in a regular pattern designed in advance. As MTMClimber mentioned, expect big-time cost overruns and schedule delays.

http://www.SlideRuleEra.net

 

[MTNClimber]

Do either of y'all have experience using air rotary?

I have. There's a chance that it will work depending how bad the rebar situation is. Sometimes they can get through it and sometimes not. A test pit showing what the upper layer looks like may be able to help the contractor make the determination if its feasible. If it's tightly spaced large diameter rebar the rig will likely have trouble and the contractor may want to increase cost for the extra wear and tear on the rig. Also, if you are already out there with a drill rig you may just want to look into using micropiles since you'll already have half of the equipment out onsite and the hardest drilling will already be complete.

 

[geojosh84]

SRE/MTN,

Thanks for your responses.

SRE,

I've seen that site you screen capped and have done some prior research into the old arena. I found some old you tube videos prepping for implosion.

https://youtu.be/4LF4FtdHqsA

It looks like they did fill some portion of the arena.

 

[SlideRuleEra]

geojosh84 - Interesting video, watched all of it, thanks. I would guess the foundations were abandoned in place, with no demolition. Hopefully, you have some drawings of the arena to be able to avoid the largest substructure.

On a difficult site we had a boring made at the center of each and every proposed caisson; about 1000 caissons. A lot of geotech work up front, but it allowed design adjustments to be made, in advance, where caisson installation would be difficult. Minimized field delays for design changes when Contractor's standby costs for equipment and workers onsite were astronomical. Not foolproof, a 4' caisson can have "problems" that a 4" boring does not reveal. Overall, geotech money well spent.

http://www.SlideRuleEra.net

 

[Ron]

Agree with many of the prior comments. If using H-pile, cut the flanges and web to create a point with angles at 30-45 degrees off the vertical. This will help punch through debris. A driving shoe will do similar, but cutting the flange and web with a torch is more reliable and less expensive.