Deep foundations -helical piles info / experience

[UK4X4]

Well I just got back from Colorado where my land is

every house within 1 mile of my plot has foundation issues

even the one built just last year.

Its not so much frost heave - but the winter water run off seems to move the light silts within the soil structure leaving areas of soil that simply just dont support the structures above.

Even though all were calculated on only 2000lbs per sq ft

The repair of the foundation on the house closest to my plot was 66KUSD

originally Superior walls over 48" of crushed rock with a concrete basement and 1-1/2story above.

The basement floor was removed and multiple micropiles installed each with a hydraulic jack connecting to the wall system.

The jacks have been left in .........just in case

In the area 2 more have had to have had the same micropiles and jacks installed.



Does anyone here have any experience of designing or had done a simple foundation based on pilings ?

We have decided to delay our build and see if the repaired foundations work- and install a pile system from day one

rather than repair later

so any input is apreciated as this is something I had not concidered to date and have no experience in

The piles set were 20-40ft deep on average and the shallowest was 12 ft

The operators seemed to think the shallow ones just impacted on boulders and stopped and the deeper ones reached high strength soil structures.

I was wondering about simply using a few larger piles and setting the house on beams with screw jacks between the piles and house and forget the concrete foundation all togther

[Squirl]

Sorry, I don't have personal experience with piles.  I have seen them on almost every beach house up and down the shore.  I could never afford one of those. What you described is about right. 20-30 ft deep on them.  I believe they also work on the friction of the 30 ft of piling sides and not just on the base of the piling, but this was just from word of mouth.  Those pilings are expensive.   Either way, if you have building codes, you will almost definitely need an engineer.  After the pilings, everything is built like a regular house (girder sizing).

Is this what was suggested by anyone around you?  Is this backfill?  Could it have been a quality issue by the installer(s)?  What kind of house was it? Brick, stone, stick frame construction?  I believe the minimum code bearing capacity is 1500 psf. 

Sizing up footing depth, width and redistributing weight can bring a building to a few hundred lbs. per square foot.  Are you worried the soil has no bearing capacity?  Maybe a FPSF would also be a consideration?   Sorry for so many questions.  I have only ever seen piling foundations as a last resort, usually in swamps or beaches.

[Squirl]

I looked up helical piles and was even more confused.  I'm sorry I thought you were talking about the treated wood piling foundations I'm used to seeing.  Checking a few of your last posts, I believe you were going for a 32x36 single story to meet the 1200 sf minimum.  I believe that would be around 136 linear feet of foundation.  I believe code is 12" wide.  Even if you were to double that to 24" wide and increase the depth to 12" you are talking 10 yards of concrete instead of three.  Concrete is $100 a yard around me, so an extra $700 to double the square feet the building weight is distributed on.  Design changes such as hip roofs can also redistribute loads.  Sorry, I can't answer your question directly, just still trying to be helpful.

[UK4X4]

Standard stem wall - failed
Superior walls and 48" gravel 4ft wide -failed
Turn down raft - failed

Litterally the spring flow moves the underlying soil arround so much that the buildings settle - Pilings being the repair method used

I'm after info on using pilings from day 1 rather than repair later

[cbc58]

The repair of the foundation on the house closest to my plot was 66KUSD.   ouch.

[Erin]

Does anyone here have any experience of designing or had done a simple foundation based on pilings ?

Could you do a post and pier type of foundation?
http://countryplans.com/foundation/index.html

I don't know about helical piles exactly (had to Google to find out what that was!) but my dad built their cabin on piers, like the second picture down in the link above, 30 years ago, primarily to avoid the cost and labor of putting in a full basement. 
But they are each concrete filled Sonotubes, about 3 feet in diameter.  The shortest one is on the west side of the house and is about 2 feet above grade.  The tallest is about 5 feet above grade.
They all go down about 5 feet below grade.

He built with the intent of just having a cheap, quick foundation.  But, it had the added benefit that when water runs down the hillside they'd built on, it just runs right under the house.  Just like a beach house in a hurricane...


All of that said, it does sound like you're in a highly erodible area.  I'm surprised you're allowed to build there...

[Squirl]

Ok.  I see the problem more clearly now.  The soil becomes a stream at all depths and shifts.  The only thing I have seen work in that type of situation was pilings.  I have seen them work in swamps, marshes, beaches, and docks.   You are probably going to need an engineer.

http://en.wikipedia.org/wiki/Deep_foundation

I'm curious about the 48" gravel 4 ft wide.  I thought with proper directing of flow and water, that might work.  Can you give more details on that?  That sounds like one of the better shots.  Maybe if you could combine that with some type of water barrier.  It seems like a fun challenge, but no one I would want to bet my life savings on.

[UK4X4]

Crushed rock footings are to avoid the frost heave, basicly no water =no frost

2 suppliers recomended that route- neighbour proves that theory wrong

Sonotubes I looked at these - the house built last year has the deck seperating from the house - it was built on sonotubes and the basement standard stem walls.

Seemingly they are moving in seperate directions

Engineering wise its a requirement in the Mesa area from county as all the soils have issues even down in the flat valley bed.

To date I've contacted 3 engineers - the three solutions from them are ones that failed on the other properties.


Visually sections of the roads are moving every winter, in the wet run off areas

the property its self shows nothing

But in the spring the test holes 10 ft deep in the lower one he hit water at 8ft.

This is the spring run off as we have a flat top mountain 2500ft above us covered in snow !


"It seems like a fun challenge, but no one I would want to bet my life savings on"

exactly !

The neigbouring property owner to mine contacted me and made sure I was aware of all the problems.......he has not built on his plot since buying it in 2002-------he actually went as far as buying and building on another plot down arround 6500ft on a rock reef.

We today purchased a 5th wheel trailer to park on the land, but I still want to progress the plans.

[ScottA]

Have you looked into a post tension floating slab?

[UK4X4]

Yes one of the engineers wanted to do waffle slab- post tension

ie a raft that supports the whole house...

so when it moves the house stays in one piece..........but to get it back level

you'll still need to micro pile ......so i'm back to square one as the micropile jobs for the neighbour was more than my foundation budget

[ScottA]

Look into it a bit more. A floating slab spreads the weight of the house out over the whole slab basically turning it into one big footing. The ground would need to move a bunch for you to ever notice it.

[JRR]

I have no experience with such a challenge ... but I tend to agree with ScottA's direction: A reinforced slab extending beyond the walls ... rectangular in footprint.  Two layers of standard pre tension steel ... 10" or more thick concrete.  ..... or perhaps just use it for an RV location.

[Squirl]

I don't know.  You would have to be pretty determined to build on that.  It took me two years to swallow the pill that the first parcel I bought was not ideal for building.  It was cheaper in material, labor, and time to just buy a site nearby and enjoy both.  My best guess would be to find the biggest treated posts you can and drive them in with a driver if you can find it.  6x6 treated for PWF or larger treated for telephone poles or fresh water docks.  All might be available in Colorado.  Drive them as deep as possible.  Build a shed or barn on top and load it up with weight.  After a year or two you will know.  Hopefully someone with some one can give you better advice than I can.

[Don_P]

I'd agree with the direction you're thinking, you'll need to bite the bullet and get down to bearing soil, that's the helical piles driven in until they hit a design resistance. The surface soil sounds like it would likely move unpredictably under a slab or anything floating on the "surface" potentially leaving large sections unsupported. I agree with the wait and see approach if you like the site and can wait to make sure that the neighbors did indeed hit bearing soils. I'd be very tempted to cut my losses.

[Rob_O]

Sounds like your *only* option is to drive piles to bedrock or hardpack. I'd spend some time enjoying that RV and see what happens at the neighbors place before I started work.

[ScottA]

Wait and see does seem like a good plan. I mention floating slabs because that's what they do here on soft ground and it seems to work pretty well. If you are on a slope I'd be concerned that piles might lean downhill over time in loose soil.

[glenn kangiser]

I have been on a project with the helical piers.  They were put in with a Bobcat attachment until they got to a certain tension then it clicked and they went on to the next one.  It was not in a real problem soil though.

[UK4X4]

"I'd be very tempted to cut my losses"

there are lots of plots up for sale, many for years - others on a quick turn around.

No really the market right now either.

The area is awesome to me with a view down to the Colorado valley and the ski resort next door,the deer- Elk and moose make
it an animal wildlife park.

No seen the moose yet,but did get to see a young bear just down the road

So I think we'll RV it for now- watch what happens to the most recent build and see if the pinned ones need adjustment.

Meanwhile research more into the helical piles

Thanks for all the input

[JRR]

If the soil is moving that much, how does one keep up with property lines and bounds?

Its incorrect to draw parallels with ocean beach property.  In human lifetimes, the soil on a beach doesn't move that much.  Oh sure, it can quickly erode in a hurricane ... or, the ocean can dump layers of sand/soil on top of existing ... but it does not seem to "shift" down deep.  This is borne out by looking at prehistoric shorelines that are now found miles inland ... there are found layers of seashells, pretty much intact.  If there was a "shifting" going on at most seasides, these shells would have been quickly milled away.

The area you described seems to be more like a river bed ... with water borne soil constantly moving down to lower elevations.  Constantly sliding "downhill".

[UK4X4]

"If the soil is moving that much, how does one keep up with property lines and bounds?"

I have road above and below so mine stays basicly the same ref the roads.......but when you google it the lines don't match the arial view

The location is on the bottom part of a steep incline 8000ft to 1000ft in a short distance with a flat top mountain above


"The area you described seems to be more like a river bed ... with water borne soil constantly moving down to lower elevations.  Constantly sliding "downhill"."

This is the way I'm reading it, not just frost heave causing the problems

My plot was cleared and level'd last year

there is no sign of movement in the level'd area or on the embancment below which is also cleared.

But in the spring the embankment was described as having springs and water flow out of it, but I can't see any now.

The next property down has a semi permenant spring with cat tails and frogs but thats 200 ft across the mountainside from me

The RV will work for now, and watch and listen to the owners of the houses with the piles in- the close one -the comapny gave him a 25 year guarentee
but really not sure what that covers...

25 years with no movement

or 25 years and we'll adjust when required !

[John Raabe]

The foundation that Frank Lloyd Wright built for the Tokyo hotel was the first massive reinforced slab and it was designed to "float" over unstable soil. It was one of the few buildings to survive a devastating earthquake. That would be an expensive solution, of course.

There may be lessons if far north foundations where they are building on permafrost. I think driven piles are also used there as well. Another expensive solution.

I've said it before, "there are some building sites that are not supposed to have buildings on them." It is good that you are finding out before you spend the big dollars.

[MountainDon]

Re: the house built last year: was it built by an actual contractor or owner built or sub contrcated? A real contractor should have insurance that would cover the failure. Decades ago here in NM a contractor built several homes in an improperly filled location. Huge cracks developed. Those homes were repaired and in some cases torn down, but the insyrance paid for all or reimbursed the people who had to have their homes torn down.


I find it hard to believe that there are so many failures all in basically the same spot. Were those really engineered solutions made by real Structural Engineers or Geotechs, with local knowledge and who actually set boots on the ground and made soil boring in order to see what is under the surface? Or were the solutions borrowed from some other site that just looked the same? Or maybe the designers were really just guys with pickup trucks full of tools and covered in dirt who called themselves engineers?

[UK4X4]

every site had a geo survey done- mine was 10ft deep

each house has to have an engineered foundation by county and HOA

The engineer I originally contracted wanted a disclaimer....against his design

Others were confident their 48" stem wall -plus back fill with non expansive would work

others were happy with prefab and the crushed rock.

Going by whats happened to all of the diferent designs ....I'd say there's more happening than the report says.


One house craked and broke the foundation during the build !

The builders recomendation of drilling test bores down to either bedrock or its equivalent sounds about right

Just need to step back a bit -wait and access whats available and for what cost

[MountainDon]

Apparently CO has many locations that are hellish on foundations. G/L

I want to see that early LR running!

[glenn kangiser]

Even drilling down to bedrock won't ensure you can stabilize a mountain mass on it's way down a hill.