Foundation design question

[scgargoyle]

We'll try this again (the last time the text wound up in another post???) I'm working on the design for our SC house, and due to the lay of the land, it will be a walk-out basement. I was told that in an unbalanced foundation (backfill on one side, nothing on the other) that the uphill side either has to have some 3 dimensional jogs in it, or have shear walls inside to support the pressure of the soil. In a normal level ground foundation, the pressure is more or less equal, and the floor keeps it from caving in. Of course, I'm going to have the foundation properly engineered, but I'm still at the floor plan stage, and want to know if I should avoid having a long straight wall on the uphill side, esp. in the SC clay soil.

[Lud]

Are you building into the hillside or is the basement's just in the slope and the view's out over the hill  or is the view downslope?

[TexasTimbers]

This is out of my league but I would want piers to bedrock with however many deadmen the engineer says you need and however long he wants them into the hill for a long straight wall. You got to have gravel backfill for proper drainage around the buried wall also i believe. Maybe its also overkill but i would also have a significant spread footing all the way around it even though if it will sit on piers sitting on bedrock. If the bedrock is deeper than your pockets and it often is, then the clay better be good hard pink clay and not a thin layer that your piers punched through when they were drilled.
It's not something to let your good 'ol boy concrete contractor do for the first time so I am glad to hear you are having it engineered. There are alot of things to consider and the soil type and layers, elevation, drainage, and alot of stuff i can't begin to consider must all be figured in for a walkout basement design.
This is where you do want an engineer with experience in this specific area of foundation work, with experience in your locale, with your soil types who has designed them with references. It can turn into a nightmare if it is not approached seriously.
If you are in a code enforced environment you probably will have to have it stamped anyway and hopefully your building inspector doesn't just stamp it because he shoots golf with whomever you hire.

I would add if the firm/person your hire to engineer this doesn't drill at least a cople of core samples over the area where the foundation will be built because "We are already familiar with the soil in this area." Then politely send them down the road. Soil layers can change dramatically from one end of where a slab will sit to the other end 60 feet away. You could have half your piers sitting on bedrock and the other half sitting on dead dinosaurs - so to speak.

[Polly]

 8)   a concrete wall longer than 30 ft will crack

[scgargoyle]

No bedrock, at least not less than several hundred feet down, that I know of.

[Jim_Rogers]

Proper placement of rebar will help keep walls straight and strong.
Have it engineered for sure....

A while ago I read a book on concrete work and it said that all concrete walls will crack, that's a given. So they cut lines into the wall or placed thin narrow strips in the forms to create a line vertically from the footing to the top.
This line is similar to the lines you see in concrete sidewalks.
It is a thinner part of the wall so that when it cracks the crack will be in this line, therefore a controlled crack location.
This makes a nice neat crack line so that you can apply sealants to crack and repair it easily and correctly to prevent water from seeping in.

If you'd like to get a copy of the book I can forward you the web page address.

Jim Rogers

[anvil]

A number of years ago, i build a log house,, 30x40 with the long wall bermed  into the hillside.  I had to have two stem walls.

No jogs in the wall.  I designed these into partition walls in the basement area.  I did have it engineered. 

anvil

[Don P]

Chapter 3 of the IRC has foundation requirements. It can be downloaded free here;
http://www2.iccsafe.org/states/newjersey/NJ_Residential/Residential_Frameset.htm

[TexasTimbers]

No bedrock, at least not less than several hundred feet down, that I know of.

If you know who drilled your well, he will give you a copy of the soil notations he made. All of the well drillers I have ever known (an entire two ) keep a logbook containing pertinent notes of every well they drill. Mine says in part (paraphrased because I don't have it in front of me).

Sandy Loam topsoil
Soft clay 2'
Dry sand 6'
Brown Clay 12'
Wet sand 19'
Pink Clay 30'
etc.

There was more notes but this gives you an idea. Mine was around 80' before he hit what he considered good water, It sure tastes good now those first couple hours of it running I thought I had got ripped off. : Anyhow this unscinetific soil notes is only at the well site. It could be different to a small or large degree even 30 feet away.

A pier driller I know very well - a buddy who started out as a professional acquaintance and who knows more about piers and soil and foundations than I could read about in 6 months, had his left arm in a sling a couple years ago and ask me to come drill some holes for him cause he needed to get this job done that day. On the way to the jobsite he got to telling me how the property owner had told the contractor to drill the piers 20' deep. the contractor told him that his drillers machine (my buddy) only went to 15' and that hard clay was rarely deeper in these parts. The home owner said "Well then drill them 15' I want them as deep as I can get them."
The contractor tried to explain they had not drilled any test holes yet and did not know where the clay was. The home onwer didn't care he wanted his slab on a solid foundation by golly and even a moron knows the deeper the piers are the harder the earth is down there with all that other dirt on it right? :D
Jimmy (my buddy) said "So jonh Doe Contractor (I didn not know the contaractor) told the homeowner he was going to have to rewrite the contract so as the slab, and any damage caused by any movement of the slab, would not be warranted. This would cover alotof stuff and could end up in court easily. i would have walked away from the job or else just drilled the holes to clay and not said any different. but Jimmy said the contractors attitude was the homeowner was a jerk and he was going to get what he deserved. I'm sorry i could not do that to a man jerk or not.
Anyhow, so here is me and Jimmy out drilling our first hole, the contractor had already flagged, and it's a fairly chilly windy day and we drill all the holes to the max depth his Bobcat would drill without the extension something like 9', then we go back and put the extension on and start to redrill all 50 something holes to 15'. the 9 footers except for a few all bottomed on nice hard pink clay. After we added the 6' extension and redrilled they all ended up in wet sand. Every last one.
So because this homeowner had it in his mind that the deeper the piers the better the resistance to gravity, he had spent more money not only initially, but no telling what has happened to the slab and brick and sheetrock since.

I undertsnad that sidewall friction offers a suprising amount of resistance to the effects of gravity, but I want my piers sitting on hard clay whenever possible. This is why I stressed to you gargolyle that you want to punch some test holes and see what you got down there and how deep and how thick. I would insist on it in fact. Code or no code. You don't want your engineer specifying a certain cookie-cutter depth for holes because his one test hole showed hard clay at 12' and ending at 14' because that don't tell the whole picture always.
Ask your contractor to supervise the actual drilling so you don't punch through the target layer your engineer liked the best on some of the holes. You might be drilling 7' holes at one end of the slab and 17' holes at the other end. Probably won't be so dramatic but it can be.

I'll shut up about it now i bet i made my point.: I  just don't want you to have foundation problems with a walkout basement design. It ain't like fixing the a floating slab on a single story ranch house. It has to be done right the first time and you gotta know that you know that you know that you hired the right people to design it and and then the right people execute the design precisely.

[scgargoyle]

I don't have a well, we're on city water there. I would imagine a soil sample in the range I'll be digging would be necessary, though. One foundation system I'm looking at is Superior Wall. There is a plant near by, and the sales rep actually lives in my (new) neighborhood, so he should know the local conditions well. IIRC, they recommended going no more than 36' without either shear wall(s) or some kind of a 3 dimensional jog in the design, to give the same effect. Superior uses 5000 psi mix, and casts the foundation in sections, which are then bolted together with sealant. Although they don't require it, I will also be using exterior sealing and dimple board. Much of the backfill up against the wall will be gravel for water control, with a typical drain system around the perimeter and under the slab. I want my basement space to be usable! Most of the designs I've come up with are in the 48' wide range, so it sounds like I need to do something to support that wall. I'll have to price the addition of shear walls, and decide if I want to go that way, or add a jog to the wall. The wide floor plan is to take advantage of the mountain view out the back- if I build a narrow, deep design, less rooms will face that way. I have a 360 degree forest view anyway; maybe I'm making too much of being able to see the mountains. I'm on a very tight budget, which means the simpler the plan the better, but not if the requirements cost more than having a slightly more complex floor plan. BTW, the grade is around 15%.

[Don P]

Our client used Superior Walls on their TF project. I have mixed feelings about it under a point loaded structure, but the foundation has been fine. Its 40 some feet along the straight back wall with about 7' of unbalanced fill, no shear walls designed, 2 installed  ;). No waterproofing, just drains and gravel, no problems. They do have a nice product.

[TexasTimbers]

. . . . .maybe I'm making too much of being able to see the mountains. . . . .

I doubt it. That's something for the rest of your life you will saying "I'm glad we scraped the extra dough together when we built this place . . . " as ytou take your morning coffee watching the orange sun coming up, or going down whatever the case may be. I'd say make the sacrifice now if it is possible to get what you know you want.

[scgargoyle]

Glad to hear some positive feedback on Superior. They do take into account TF construction, to make sure the point loads are adequate. I was skeptical about the foundation resting on gravel, rather than a concrete footing, but after all, the concrete footing would be sitting on.... gravel. And TexasTimbers- would ya please give that dawg some grits? He's driving me crazy! :D

[TexasTimbers]

I know exactly what you mean. There is only one avatar on the whole forum which I don't like to look at but I find myself avoiding his posts because of it. So - in light of the wrong way mine rubbed you I fed Red some grits (well not really but maybe this one won't distract you as much).  ;D

[JGroebner]

If you remove the hydrostatic pressure caused by the clay it'll help extremely.  This can be done with Gravel backfill from the footing to the subfloor allowing the water to drain down to the footing and out through the drain tile.  The water in the dirt/clay Dwarfs the pressure caused by the dirt alone.

Secondly, you can specify that the mason has 4 horizontal runs of rerod over an 8' height and vertical rerod 2' o.c.  I would also suggest that the footings have 4' bars bent over 2' and up tied to the vertical rerod.  You can also specify the slump in the concrete when it's delivered, this will severely increase the strength of the concrete as it'll remove more of the pockets in the pour.

steel = strength

Jared

[scgargoyle]

Great info, Jared. There will be a lot of gravel backfill, with topsoil at the surface.