Wind towers foundations and helical anchors

I've seen some claims of greatness from the helical anchor industry, but I see very few actual installations. I don't have a perfect answer as to why, but we in the US are very slow to adopt geotechnical advancements.

Are you looking to deal with compresive loading or pull out strength? Probably both, I'm assuming. Will there be a concete cap on top of the piles? Will it handle long term corrosion possibilities like the minipiles (or caissons, hard to tell from your description) will?

Before I went with anything beyond the tried and true, I'd like to see the actual in-field test results, and would want to see long term results. Also, these foundations are often installed in lesss than ideal situations for helical anchors, like rocky hilltops, where they can't be economically installed, like you said.

Sorry to ask more questions than give answers.

Thanks for the reply. Mainly pull out strength is required, since the system is predicated on post tensioning with a large reinforced concrete cap. Unless the site is all peat bog, coal or cinder all highly acidic soils, there is no reason to be concerned with corrosion anymore than with concrete pilings, I think...

We've been experimenting in conditions similar to the project site and have had great results with a load bench test. The most notable change is the speed in which we can install the anchors, with no waiting/curing time to begin the post tension process.

Hey Jeff,

I'm not qualified to speak to the PE. side of this question, but I do know the money side of the business - sometimes. You might try a test site, showing your client the the savings and a program that would be followed to keep secure the new technology's use and If they , the Anchor Co, want your business and are an un-proven & time tested in this application , they might purchase a surety bond , with you & your client as the also insured, to cover the potiential replacement cost, should their system fail. Then you monitor the test site on a regular basis for a small fee, everybody share the data and this becomes everybody's, newest advertising vehicle . Your service, of monitoring for the small fee might be a good deal for the client, as they are saving mega bucks on a install.

Just a thought, that might keep you clean, with all eyes open, if it all fails.

Best Regards,

Joe Woodall, Managing Partner

Georgia Adobe Rammed Earth & Renewable Energy

2395 Bowman Hwy. NW.

Dewy Rose, GA 30634

706-213-7693

www.georgiaadobe.com

I agree. If they are claiming something and you have a need for it, you should be able to negotiate a test. I have a feeling there will be shear factors that are not included in their claims. Just a gut feeling, but something to concider.

Hi,

I saw some recently in central Europe: all relying on a flat concrete block,

up to 18 x 18m square and 1 m thick, highly reinforced with a lot of steel.

Construction ground below was geologically old sediments or volcanic material.

Into this concrete block big steel anchors are secured to which other steel or concrete elements are mounted for the tower construction.

Cost is up to 150 K$ (100K€). (concrete base only)

RHABE

I really can't comment on the helical anchors but I have to say that $60k US for the concrete work seems very high. I was just quoted $63k for the installation of a 10kW wind mill with all site work, the wind mill, etc. included. Basically a turn key operation. It's still upside down for 18 years, so I don't think I'll go ahead until I can buy a couple of Chevy Volt cars and "pump my own," so to speak.

Hi,

the 150K$ cost of concrete plate foundation was for a 5 MegaWatt windmill.

RHABE

now that's a lot bigger. Wish I had one of those!

Me too, the ultimate para-sail obstical course >:D

Hi, Jeffb!

Does the helical anchor lower the center of gravity of the installation? If it does, then there's a shear and bending stress advantage in replacement age, which might translate into dollar savings over the long run.

Mark

Jeff-

What type of base reactions do you have? Our clients utilize a "concrete-less", shallow foundation system supported with helical anchors for their towers. My guess is that the loads are substantially larger in your application, but perhaps it could be modified for such.

Our clients save about 25% versus a conventional embedded pole-foundation...no spoils, rebar, concrete, dewatering equipment to deal with not to mention fast installation.

Daniel

starkd@starkfdn.com

Jeffb, I have used the helical type anchor for years. I help introduce them to a large open pit mine in Northern Alberta. The use was for an outdoor substation. The buss work, towers and transformers are installed on the top of the helical (foundation) anchors. The anchors are made from >schedule 80 steel and can be hot dip galvanized. A three inch pipe with a 3"&7" helix has a bearing strength of 50,000 lbs downward/upward, class 3-5 soil. This small anchor can be put in using the run of the mill utility truck. The surface material does not matter as these anchors can be joined with extensions and drilled in deeper to the proper torqued required. Only one lead is used.

I did a field test with a 6"-2 12" helix-10ft long anchor. I first drilled the anchor into sand (tailings) and had a D-11 with a ripper attempt to pull it out. I end result was the D-11 ended up with the front blade in the air, about 12 feet and the anchor did not move. We estimated that the force on the ten ft section was greater than 150 tons. I then had the crew screw out the anchor to examine the flights and found that the anchor would be acceptable for re-use.

All the towers in Northern AB ,for a large double circuit 240-500kV power line use this type of anchor for their bases. The anchors are drilled in at a thirty degree angle. Three are used to support each leg with a base plate welded to the tops to secure the leg. I have used these type of anchors for a single free standing 140' pole. Three were used as a base and four others were used at the corners of the plate. The area under the plate was filled with concrete. The reason was that this structure was beside a highway and the engineer felt that people driving by would feel more secure with that look. The concrete was 20 MPa with no re bar added.

When it was time to move this structure, the concrete was broken with a sledge hammer and the pile were screwed out and salvaged. There are many companies that engineer, supply and install anchors here in Alberta.

I think that 8- 14" c/w 22" helix-34 ft long would do you. The steel that you would use as re bar would be more than the steel in the anchors, never mind the concrete forming and pour. Yes BELIEVE your anchor supplier.

Hi All

i have designed and installed helical piles with ultimate test loads of 850 kips. piles have to be properly designed. the supplier should provide to you his caculation to prove his point. feel free to submit his design to the DFI Helical pier committee for review. i am a member in the committee and willing to help, thanks

Hi, Mamdouh!

Welcome to CR4!

This discussion was quite interesting. I'm certain that the original poster will get your message, because we tend to keep topics of interest around for awhile, just in case somebody like you joins and can offer some help.

You've already discovered that the wide range of topics in here can provide areas of interest for you.

I hope to see you around the blogs in here in the future.

Mark

Many of the helical anchor manufacturers tend to give you the structural capacity of the pile . they ignore that the pile will fail geotechnically before it reaches its structure capacity. let him submit all supporting documents to you showing the load tests and pass it over to us at DFI- Helical committee and we will be willing to give you some advises, thanks Mamdouh

Hi, Guest!

Are you contending that helical anchors are inadequate, or are you hinting at a design flaw where the load capacity is given as actual rather than having a safety factor built in? Is this DFI Helical committee working towards a standard?

Mark

Jeff,

What state are you from?

We are in The foundation Repair Business and also installing wind turbines / towers with helicals.

Kevin