Piled foundation

[Michael34]

 I need to decide on the type of foundation for a 1 storey house 20*15 ft, design load 100.000 lbs; soil - sandy clay with high water content,  freezing depth up to 7 ft. Monolithic slab or continuous strip are not being considered.  I  was thinking of a piled foundation, but  I dont about what shape and depth of a column. It seems that this type does not exist as I could not find any technical descriptions of it, although many people are using it. For example the international residential code IRC only addresses slab, continuous strip foundations. The only suitable types that I saw in literature were pile and beam (deep piles with small pads on ends connected above ground with concrete reinforced beams forming a strong frame ), pad foundation. What if I use concrete pads with precast cubes placed on them (without steel reinforcement ) and lay frame of thick timbers 6"*20" instead of concrete beams? It would be shallow, above freezing depth, although there would be no much lateral pressure since they are pads. If such foundation type exists I would really need references to technical documentation, codes and information on how to calculate and construct it properly. 

[beenthere]

Pls add your location to your profile.. helps to know about where you are in which country.

Also, by the forum rules you put your images in your gallery (can see rules at bottom of the page).

[scsmith42]

Lots of pile foundations in southern Louisiana; that would be a good state to research literature.  Most of what I saw there was the pile and pad style, with a field of piles driven to refusal and a concrete cap poured on top.

Are there any local pile driving companies in your area?  If so you might want to consult with them for recommendations regarding either literature or an civil engineer familiar with pile foundations for residential use.

[jwilly3879]

Try a search of frost protected shallow foundations. They work very well on expansive soils and very little excavation is required.

[AlaskaLes]

Michael,
We own and operate a pile driving company in Alaska.
I can help you work through a couple of your questions and point you in the right direction for some of your others.

If I understand your post, you are building a 20' X 15' single story house.   This is nowhere near a 100K load, even with 4' of snow on the roof.

As stated before, it would help to know your location just to have a better idea of your freezing/flooding tendencies and the level at which you would encounter permafrost and freezing/jacking and thawing of the upper layer of your ground.

The standard piling in this state is a 4" I.D./ 4.5" O.D. pipe.  They are used by the drilling companies and then sold after a few uses.  We buy them at a much reduced rate from new and typically drive them in 20' lengths, striving for a minimum of 15' in the ground.  We recommend that our customers (using this size pile) not exceed a grid pattern of more than 8' to 9' between piles.  This helps to minimize shaking and movement of the finished structure and also helps to avoid overloading of 1 pile in the set due to the particular load of your house and it's contents.

These are referred to as friction piles or cohesion piles as they will typically rely on the friction between the ground/soil/gravel and the surface of the steel piling (both interior and exterior surfaces).
Depending on the ground we are driving through/into we will sometimes encounter a pile that will be driven to refusal (till it won't drive any further), or we will drive a 20' pile-then weld another onto that and keep driving till we get enough friction or drive to refusal.

After the piling is set, usually 1.5' to 2' will be out of the ground.  Steel brackets (we build these) will be set on and into each pile and glu-lams; solid wood; or steel beams will be laid across each row of pilings and then the floor joists will be laid at 90° to these.

If you are planning on leaving 4' to 5' of piling exposed for storage or better flood clearance, I'd look at welding steel brackets and wood braces, or steel angle braces between the elevated pilings to increase rigidity and counter possible side loading. 

You have mentioned freezing a few times and this will usually cause a finished structure that is above ground (resting on concrete piers and pads on the surface of the ground) to be moved up and down quite a bit as the upper levels of the ground freezes and thaws (expands and contracts).  Clearly there is nothing good about movement like this and it will result in your finished structure being cracked and or slowly ripped apart.

Hope this info helps you and I'll keep an eye on this post to see if you have any more questions I might help to answer.
Les

[AlaskaLes]

The other point that I want to make (thanks to the post before mine) is: if you hire an excavator to dig shallow foundations and then pour concrete...you have typically already paid more than the driven steel pilings would have cost you.

I'm a bit biased, but not because we make part of our living from driving pilings, rather because we already did all of this research to satisfy our own construction needs and came to these conclusions after much learning and studying.

The other nice thing about steel pilings is that you can pour a concrete foundation or concrete sonotubes and you still have to wait a week or more to start building on them.  Whereas, you could be building on steel pilings immediately after the hammer has moved away from the pile.

[jwilly3879]

I have seen screw driven supports used around here by sun room companies (Techno Posts?)

[AlaskaLes]

Those are called Helical piles or Continuous Flite piles.

Generally used in locations/substrates where there is not much rock or gravel and instead has a high concentration of sand/silt/clay.

[jwilly3879]

As the building inspector they gave me the sheets showing the torque values they drove to and the info to convert that to bearing capacity.

[AlaskaLes]

That makes sense for a screwed in piling.

We're using a Corps of Engineers formula for our double acting pneumatic hammer as a means of estimating the bearing load of the piles.
They refer to it as the Engineering News Formula Soil Penetration Test.  They have several formulas actually and your type of hammer dictates which formula to use.

Basically, you wrap a piece of paper on the piling and set a straight edge level with and several inches above the ground level.
Within the last 6" of the drive, you run a sharp pencil smoothly across the straight edge as the hammer is running and it looks like an EKG (heartbeat) at an angle.
It will show the set, or net drive(gain) of each stroke of the hammer.  You mark a horizontal line at each set line and measure the distance between them.
Plug that data and the lb/ft of energy that your particular hammer generates into the formula and the result is a load rating for that particular pile.
I'm not sure what other people are using to estimate the bearing capacity of their driven pilings, but this method seems to work pretty good for us and it gives the customer a good idea of what their soil and pilings with support.

[jdtuttle]

We call that type of construction a grade beam foundation. Around here we have a 42" frost depth & it works well for exterior concrete porches & post & beam construction.
http://en.wikipedia.org/wiki/Grade_beam

[Michael34]

Hi Alaskales
The house would be rather light 40 k lbs design load, around 1600 per pier.  What you referred to is a classical pier and beam foundation and I would go for it without any hesitation if the budget wasnt so restricted. I did some inspection of the houses nearby and found out that those which are not on continuous type (slab, strip) have piled foundation to below freezing level either concrete columns (with rebars inside) or steel tubes (there are also ones that can be screwed into the ground); I saw another house on a foundation made of blocks lying on  a mat of sand and gravel mixture filled into  shallow holes above freezing level (just with the top layer of black soil removed, so its about 12-15" deep). The owner said the were some minor deformations in spring, some times a door does not open/close properly, but on the whole its ok; the piers heave and subside altogether, so theres no much difference between them. In what I want to build the only difference would be that I place the precast blocks onto wider pads which in turn would be surrounded by a layer of non expansive mixture of gravel and sand; unstability of piers would be compensated by a frame of thick main beams resting upon them. Have you seen anything like this? By the way it seems you are building in warmer areas of Alaska because in permafrost there perhaps no need to dig into the ground at all; my building location is not so cold although the freeze depth is 7'. Are there any textbooks, manuals describing how to calculate the heave force and elevation itself based on type of soil, shape of the footer?

 

[AlaskaLes]

Permafrost actually defines that level underground at which the thaw doesn't reach.  So you may have a 4' or 5' of ground near the surface where it thaws and freezes with the seasons.  Under that there is frequently a layer of frozen ground that runs for a few or several more feet that is still above the thawed ground beneath, yet is below that section which thaws in the summer from conduction of heat from the surface level.

We are indeed in the area where this isn't quite as thick as more Northern locations in the state.  These days, we aren't getting the brutal winters that we were in my high school days.
               
If you get one local guy who says he's not having any issues with his pad, I'd make note and look for more examples to back that option up. 
That might be an option for you.
I can relate to the budget limitations.  We started with the simple sonotube pilings and they were horribly mobile.
Wish we hadn't done that one.  That's what led us to our current pile driven option.
No, I haven't seen anything exactly like you are planning.
I have seen many unique ideas for people's cabins and houses, but most don't look nearly permanent for my tastes.  I'm frequently telling people that I have way too many projects planned to be building them twice. 
Not sure of any textbooks, but I would do some serious searching with regard to cold climate foundation designs and see what you come across.   You might even search under Corps of Engineers Cold weather designs.  They have a huge budget and are frequently called on to provide answers to these problems.

[Michael34]

These are some images of this design.
 
In this link  http://ana-white.com/2015/04/building-remote-cabin-foundation-mucky-soil it is the pad and post foundation and its been done in Alaska. Also I found pads mentioned in the Alaskan log home construction manual in addition to deep driven piles like yours. There even wooden pads were described placed on a bed of gravel directly upon undisturbed vegetation. So what are the drawbacks of this foundation type? When it would be moving up and down after a first winter I can level that up with a jack and wedges so the settlements would become more even. The question is how big the elevations could be; would that really do any harm to the structure and put people in danger or is it mainly for aesthetic reasons that people dont want to deal with these up/down movements and choose a slab or piles below freezing level?

[LeeB]

Never lived anywhere it gets that cold and don't plan on moving that way any time in the foreseeable future. Just making a guess here, but I suspect plumbing would be an issue with very much movement. You would have to have some kind of slip joint or some othe way to deal with the movement and your piping.

[AlaskaLes]

Michael,
Sorry for the slow reply.  My buddy and I have been in a very good Timber Framing course for the past 4 days and I'm just now getting back to the world around me.
I've seen several of these variations used in many projects in soft and highly mobile ground.  Some varieties have been: 55 gal drums filled with dirt, sunken in the ground, and filled with a post surrounded by dirt or gravel: Sections of culvert filled with gravel and a wooden post set in it: concrete filled sono-tubes with and without the flared footings: and probably a few more that I can't think of right now.  Sometimes they work and often they will work to some degree.

I have seen the type you showed in the photos too, but they just haven't held still enough in my area.
If you've got ground with a heavy gravel concentration, it may not move as much as ours, but this just doesn't stop moving where we are.

We have several sheds and outbuildings on those piers and they will tilt and tip and eventually we have had to jack up, fill-in, and reset the piers to keep them from just flat falling over with the buildings.

Regarding the adjustments needed to straighten the building back out, we have had to jack: shim: crib: jack some more, until the building was relatively level and the doors would close again, the walls would touch the floor again and the grease in the pan wasn't all to one side.   Not necessarily dangerous, but not good for your house and it truly sucks to watch those things that you've built try to break/work themselves apart.

Your results may vary from ours and I really hope they do...lol.
Les