How to verify grouting of a pile

[Brian12345]

The situation: We have a pile(s) with a large cavity around the mid - section. we plan to dig down to the cavity, fill it, then pressure grout around the pile.

Question: how can you verify that the grouting has worked, i.e. the uplift capacity of the pile has been restored?

 

[hokie66]

What kind of pile? Is the "cavity" in the pile itself, or around the pile? What caused the problem?

 

[Brian12345]

Its a augered reinforced concrete pile, the cavity is around the pile. We think it was a combination of the augering process and the natural ground.

 

[hokie66]

In that case, I'll have to defer to others. Don't have experience with augercast piles.

 

[Ron]

Is the pile reinforced past the cavity? If so, the uplift capacity remains, since the concrete contributes little to the uplift capacity, other than soil-pile interaction.

Since you are exposing the breach, then you can visually verify the grouting.

Use a jacket with air/grout vent on the opposite side.

 

[PEinc]

I'm confused. I can understand having a cavity in an augercast pile, but how do you get a cavity around an augercast pile? Doesn't the cavity get filled with pumped concrete as the auger is withdrawn?

http://www.PeirceEngineering.com

 

[Brian12345]

Sorry for being vague.

The auger cast pile has a steel tube surrounding the concrete. The tube was driven into the soil in sections then the soil was augered out before another section was welded on. We think the auger went down further than the tip of the tube and caused more soil to be removed from the outside of the tube. When the next section of tube was welded on and driven the cavity remained and was not filled with concrete when the pile was cast.

So, now there is a significant amount of pile not incontact with the soil which reduces the uplift capacity.

After we have filled the cavity with sand and grouted around the pile how can we verify that the soil/pile interface has been restored?

Since there is a steel tube we were thinking a resistivity test or a PDA/CAPWAP analysis before and after grouting. But will these work or cause significant displacement? Is there a more conventional test which can be carried out.

Hope that makes more sence?

Thanks in advance.

 

[Ron]

Do a tension load test on the pile.

Your pile is not a typical augercast pile. I doubt that you have the same soil-pile interaction characteristics as a typical augercast pile, so hopefully augercast friction estimates were not used in the design. The skin friction on a steel pipe pile, filled or not will be lower than a typical augercast pile.

 

[Zambo]

How deep is the cavity? How will you support your excavation when you excavated down - sheet piles? A steel caisson?

You have 2 issues. Firstly, the area where there is now a cavity which you want to restore to the same skin friction resistance (on a steel pipe) as there would have been if there was no cavity. Secondly you need to backfill your excavation and compact well so this area is of similar condition as the natural soil.

I suggest backfilling the whole excavation, including the void with a lean mix concrete.

 

[Riggly]

First of all, this is not an auger-cast pile. This seems more of a driven pile. I do not think that load test will verify whether your soil/pile interaction at that location was restored, but it can verify whether you have enough uplift capacity (what is the size of the pile?). By they way, how much soil loss (length) you think occured? And what percentage of the pile length was that? How deep did you think it occured? Why did you use a steel casing? Typically there is no casing in auger cast, and the pressure of the concrete keeps the soil out. You said that you filled around it. How was that process carried out? Wa it? What type of soils are we in? Where is groundwater? The only other thing I am thinking to actually see whether there is still some cavity is a geophysical survey. How many of the piles had that problem?

 

[Zambo]

Riggly, you are correct it is not an auger-cast pile. The threadstarter Brian12345 I belive correctly described it in the third post as an augured reinforced concrete pile. So it is excavated by augur not augur-cast.

It is not a driven pile. It is either a bored pile or some type of micropile.

 

[hokie66]

I probably contributed to the confusion by referring to it as an augercast pile. Agree with Riggly and Zambo, sounds like a cased bored pile, with the casing remaining in place.

 

[BigHarvey]

The easiest way to restore or even improve initial conditions would be to carry out compaction grouting around the piles provided you know which piles to treat and at what depths.

This being said, I don't understand the use of the steel pipes. if you look for friction, concrete should be prefered to steel !
I wonder how your piles are designed : driven or drilled ? Given all the question marks about these piles, I suppose a load test would tell you where you are at this point !