chemical grout to enhance helical pier capacity

[jcraig]

I am looking for information, case studies, papers, design examples, etc. for the use of chemical grouting to enhance the capacity of helical piers.

Questions I have:

Has the been any case study developments in this application?

What are the parameters for the size of the grout ball (saturation) required for different soil densities and pier types?

What conditions are needed to achieve the desired saturation?


Any help or leads is greatly appreciated.

 

[PEinc]

I am unaware of any uses of chemical grout to enhance the capacity of helical piers. Did you try contacting the helical pier companies such as Chance, Atlas, Ram Jack, etc.? Chemical grouting would help but would have to be done after the anchors are installed or else you could have trouble screwing them into the improved soil. Without much testing of the grouted soil for engineering properties, I'm not sure how you could confidently design the piers for improved soils. Designing helical piers isn't a very exact science even without the grouting. And soil groiting is a little bit of voodoo! There's no way to guarantee that the soil will improve at each pier location. Overall the soil mass may improve on average but maybe not at individual pier locations.

Are you underpinning? Why did you decide on helical piers?What is the design load per pier? Are you using the piers to support vertical loads in compression or are you working with helical tieback anchors? In either case, it may be cheaper to use drilled and grouted tieback anchors or mini-piles. They can usually be installed deeper than helical anchors and may be cheaper for higher design loads. The additional cost of soil grouting could make the helical pier system more expensive than drilled and grouted anchors or mini-piles.

I think I would look for another method rather than try soil grouting.

 

[Focht3]

What do you mean by "chemical grouting"? Why are you grouting? Please give us some more project specifics -

 

[jcraig]

Chemical grouting is a method for improving loose or poor soil conditions using a low viscosity grout that is commonly a polyurethane or acrylate material. The low viscosity enables a strengthening mesh to strengthen granular soils or fill voids, greatly improving the site conditions. This method is used over cement grouting especially where seepage control and water is a problem. The chemical grouts commonly used are fast setting and can be either rigid or flexible. They can have either hydrophilic or hydrophobic properties.

I do not have a project that I can personally provide as an example. The helical pier application for chemical grouting does not appear to have been used very often, although I have heard of contractors using this method to improve poor soil conditions prior to installing helical piers. This is why I was hoping to find out if any studies or anything more than "voodoo" information was available. I wanted to find out if actual designed methods are being used.

Thank you for the lead to Chance, by the way. They do have some case studies and design examples using grout in helical pier applications.

http://www.helicaldrilling.com/techlit.asp

I also located technical brochures on "micro piling" here that uses a grout application as well, although it appears to be cement grouting.

http://www.helicaldrilling.com/brochures/pulldown.pdf

 

[Focht3]

Please post any information that you may find on this message thread - thanks in advance.

I'm familiar with acrylate and urethane grouts; jet grouting as well. A different chemical injection process (which could be considered as chemical grouting) is used in central Texas to modify expansive clays and reduce the shrink / swell potential. It uses a high pH potassium solution, wetting agent and water. (The original formulation used table salt as well, but the salt was a remnant from the solution's origins in the oil field. It did not affect the chemical reactions and has been dropped from the mixture.) If you had proposed the potassium-based solution with helical anchors, I would have cautioned against the combination. The potassium-treated soils become quite friable, lose much of their "cohesiveness", and act more like sand. It's an amazing transformation - but could wreak havoc on uplift capacity.

 

[clayR]

Jcraig,
What you are proposing is interesting..... solution grouting to enhance the capacity of a helical pier. Given enough money you could make it work providing you have soil that can be penetrated by the grout(a rule of thumb is <15% passing the 200 screen). Perhaps a more cost effective approach would be a method using fracture grouting techniques and cement grout, and not rely on pentration of the grout to enhance capacity, as the system you describe now would be limited to primarily sands.
As far as a method for grout delivery, mixing in 5 gal bucket and dumping down the hole is not acceptable, as shown on the link in your previous post. The grout should be placed by use of TAM pipes or injection pipes placed after the helical is in place.
To make the system cost effective only the lead sections should be grouted, and this should be accomplished without drilling additional holes to place the grout. The ideal delivery system could be to combine the tam pipe method and helical pier so grout could be injected through ports in the wall of helical, via straddle packers. I know that helicals are now designed using a pipe section so maybe this has already been done?
I hope this is relavent to the topic....vty clay

 

[PEinc]

This grouting idea sounds like it is getting more expensive with each new response! jcraig still has not indicated what he or she is trying to accomplish, what the piers are needed for, what the soils are, what the design loads are, tension or compression, tiebacks or vertical piers. With the very limited information provided about this project, I am inclined to think that helical piers may not be the appropriate solution.

 

[jcraig]

Sorry for delays in my responses, it's been a busy week for me and I can only log on sporadically.

As I stated in my reply above, I have no project personally. My work is primarily in R&D and the possible application of using chemical grouting to enhance poor soil conditions with helical piers has been posed to me.

I myself, believe that the cost analysis would prove too expensive, in lieu of a more traditional and formally designed applications, but when I discovered that some contractors may have already been trying this (hearsay for which I don’t have specifics) I wanted to see if there were any case studies or design methods developed. The best I can find is on the Chance website link for micropiling which I posted above.

Again my original intent is to investigate the following questions I had when the question was originally posed to me:

When would the obvious expense of chemical grouting the soil be outweighed by the improvements in load capacity or the general site improvement? For an example, I would like to investigate conditions like Florida with peat/organic soil situations and the potential for sinkholes. In other words, what are the economics of large amounts of cut and fill, large equipment mobilizations, time and labor, etc., verses fast setting chemical grouting and quick helical pier installation, with smaller equipment requirements.

Site staging space would be smaller as well and I would think you could install closer to existing structures or sensitive vibration areas better than more traditional foundation methods like caissons or driving piles.

The economics, of course, is a mute point if there are not good solid design methods and if the load capacities cannot be theoretically determined. How do you determine what your improved soil emulates for bearing capacities and bearing soil factors? I agree with the uplift dilemma as well. I have only questions, with very little information to provide a real world scenario.

I do, however, appreciate the responses immensely. Besides the Chance micropiles, this thread also led me to the Geopier website which is an interesting application as well that I would like to look into more.

http://www.geopier.com/

 

[ruslindsey]

ruslindsey(R&D Helical Piers)
In reponse to the use of grouting with helical piers,
there is a company that has a patent on this.
the results are outstanding,also they have a patent
for attaching piers to rock.

 

[PEinc]

So, is the company's name a secret?

 

[ruslindsey]

ruslindsey(R&D Helical Piers)
company name that has this patent is Turbopier Industries
a division of Precision Pier USA,Inc.
Contact person:Engineer Stan Rupiper Phone#530-525-4560
Contact person:Sales Mike Lugwig Phone#303-901-1579
I'm sorry for the delay.