Compacting house pad

[herdfan]

My builder has a dilema, which is giving me a headache!

Before my question, I have to give a little background info.

We are building a home with a walkout basement, and the garage is off of the first floor. There is a creek down the center of our property, which we have contained in a 4' culvert and covered over. The basement floor of the house is above the level of this creek. The edge of the garage runs adjacent to this culvert pipe, but does not go over top of the pipe.

So - basically, we are building the house and covering up the front of the basement with fill to make a house on a hill with an exposed. walk-out basement in the back. The dilema is with the garage on the first level. The garage base needs to be built up with fill as well to raise up the garage footer to the first floor. The second floor of the house is built on top of the garage, so the garage footer is pretty important. Our builder says that he can't compact the fill appropriately because it's too "spongey." The fill he is using is mostly red clay. He is now saying that he may have to dig down under the clay (even though he spent the past 2 days putting this in in 6" lifts) and lay in a footer, lay some block up to the 1st floor level, and then fill this in with compacted gravel.

This sounds a bit overkill to me (not to mention a bit costly), but I want it done right. Would a different type of fill work? Has anyone had this problem come up? I've seen house seats being built up with fill, but haven't ever seen a footer poured and then the entire house built up 8 or 9 feet on block before!

Does it sound like this guy is on the ball or should I start looking for another contractor? /forums/images/graemlins/confused.gif /forums/images/graemlins/confused.gif /forums/images/graemlins/confused.gif /forums/images/graemlins/confused.gif /forums/images/graemlins/confused.gif

 

[dltimmons]

It may not be the type of fill being used, but the underlaying soils that are the problem.
Do yourself, and your contractor a favor, and hire a proffesional, licensed, structural engineer, to do a set of engineered foundation plans. First thing to get is a soils test, this will tell the engineer the bearing capacity of the soil, and allow him/her to design the appropriate foundation.

A foundation should always rest on undisturbed soil, with a sufficient bearing capacity. It is never a good idea to build any foundation over fill. If fill is required, structural fill, compacted in no more than 6 - 10" lifts is normally used, and then a soils test should be performed before pouring any footings.

When the existing soil is either unfit for a normal foundation, or has expansive properties, usually caisons are drilled down to soil with good bearing, and the foundation is poured over the top of these caisons.

The last thing you want is to get your new house done, and a year or two later, have doors that wont close, cracks in the walls, and your garage breaking away from the house.

Find an independant engineer to look at this. It should only cost $500.00 - 1,000.00 and it could save you a whole lot more.

If you have a walk out basement and your garage is on the first floor, the rear wall of the garage must act as a retaining wall for all of the fill inside the garage plus the load of the concrete floor, plus the weight of any autos etc. inside the garage. This wall may or may not be exposed at the rear of the house, but construction of it needs to consider all of the above.

I can't give you any better advice without a lot more detail on your building site and home design.

Good luck,

DT

 

[neilly2]

The fact that this moron put clay material under a structural element (even a slab) during a two year rain, makes me cringe.

I hope this guy is on a lump sum contract. If he's trying to get you to pay for this mistake tell him to get bent. Or give me his number and I'll call him. (i'm not kidding I have unlimited long distance). It drives me crazy when people screw over other people that don't know the particulars of the business.

I recently put a building up back on the East Coast over wet silts and clays (this was the virgin material). If we put more poor soil over it, the soils engineer would have flipped. We dealt with it by putting a layer 3-4' of stone. We started with 4" stone and pounded it into the poor soil then came up with 3/4'' clean and DGA(road mix). What this does is bridge the poor soils. Then we came up to bottom of footing elevation with structural fill.

I can get a lot more detailed with your project if I get a few more particulars.

Some questions-

Who designed the house? The builder should be consulting them.
Not many Non-mansion homes have to be concerned with soil bearing capacaties, so doing a test of the soils would be a waste of time. Just make sure there are no sink holes in the area.

You need to worry about compaction which if you do not have you will get differential settlement as the cause of cracks. Compaction is a function of soil type, moisture content, and density.

If you are concerned get a geotechnical engineer. However, this sounds like a fairly straightforward issue that the Architect or knowledgable builder can handle.

By the way, the moron builder is on the right track with the gravel, but his idea of putting a footing down to virgin soil could actually do more damage even though it may seem stronger.(in fact if I am picturing the issue right he's definitely going down the wrong road) I can give you more detail on this if you wish.

Virigin soil is not necessarily buildable, it can have adequate bearing capacity but if not properly compacted and stable will be useless

If your desinger has your plans on AutoCAD send them to me and I'll take a good look.

Sorry for the disjointed thoughts but I can barely keep my eyes open.

 

[herdfan]

Thanks for the replies, guys.
I don't have the plans on the computer, but the plan is this one online House Plan
The basement is essentially the same as the first floor with the garage area being unexcavated earth on the plan.
I'm thinking the problem may be the soils in the creek be, because the soil for the rest of the basement (away from the creek) has just a little clay in it and it contains quite a bit of shale. The contractor dug down beside the culvert pipe to a solid base (although it was clay) about 5 feet below grade and then compacted in the fill (predominately clay) in 6" lifts with a vibratory roller.
He did say that he was waiting on a call from some guy to let him know what to do (but I think this "guy" was the one who told him to lay down the footer on the clay and then go from there). I'm trying to find out who this "guy" is, exactly.
The bigger issue is, obviously, does this contractor know enough to do this job correctly? I surely don't want a detached garage in a few years! /forums/images/graemlins/blush.gif

 

[DiskDoctr]

Herdfan,

Nice house plan, sharp looking.

I am more from the world of "yeah I shoulda done this ahead of time, but now what can I do to alleviate the problem."

First, let me warn you that I am not an expert in this area. Anything I say should be discussed with your contractor(s) or engineers as "would it help to ..." then go with what they say.

Could you use sonatubes to make a pier type foundation? Basically, dig some deep holes to solid material, place these forms in ground and fill with concrete to make pillars. Then your floor structure could use these.

I've seen people use these for partial support (floor still rests on ground and these pillars act as anchors), and as complete support (beams and support structures don't touch ground anywhere except on the piers).

I've also seen a commercial building put up where it was necessary to dig out all the earth to at least 5 feet deep and replace it with different material (shell, I think). This was a large manufacturing facility with a bunch of CNC machines and such.

If it's any consolation, these builders (very experienced and well respected) didn't know this until they started excavating and weren't satisfied with the results from the compacting efforts.

Whatever you do, don't take chances with your new home. If you skimp now and you have troubles later, you'll never forgive yourself. Also, don't try to rush it and compromise because you are anxious to move in.

Of course, this is just my opinion and some suggestions. Really hope it works out quickly for you.

Let us know what you work out.

-JC

 

[johnday]

Herdfan; look at your PM's and talk to me. /forums/images/graemlins/cool.gif

Also go on line to JLCOnline.com and go to building science, we even let layman ask questions /forums/images/graemlins/smile.gif

 

[EddieWalker]

When I was in California, one of the residential developers I new put in a tract of spec homes on the side of a hill. He had earthquakes to deal with, so the footings had to go down 20 feet or more in places. I don't remember the specs, but the total foundation, per house was in the neighborhood of 140 yards of concrete for 2,000 sq ft of living area. These homes sold for $500K and he said he didn't make 10% on them.

Good luck,
Eddie

 

[Darren]

There's more involved here than just compacting the soil in 6" lifts and doing a compaction test. For one thing soil mositure is critical. If it's not within a certain range, you won't get the compaction needed no matter what. I've seen high clay content soils actually sink under a load and then spring back after the load passes. Depending on the type of clay you could also have shrink and swell problems.

Clay is absolutely the worse material your idiot contractor could have chosen. You're guaranteed to have problems with the basement walls you've backfilled with clay.

The other potential problem is the creek. Given the increase in flash flooding in West Virginia we've seen, you've got a problem sooner or later. You're building in a floodplain. I'm not sure how you got a permit, if the county you're building in enacted an ordinance based on the FEMA requirements to enable residents to buy flood insurance.

WV has a lot of problems with the way the permit process is being conducted in some counties. If you're in one of those, the county isn't doing it's job and they just haven't been nailed by FEMA yet. FWIW, that comes from the state flood insurance coordinator.

BTW, were you required to get an elevation certificate to apply for the permit?

 

[herdfan]

I talked with the builder again today and he is arranging some soils testing.
The creek shouldn't be a problem. It is basically a collection of 2 smaller creeks from the hollars at the back of our property (mostly runoff, but some springs too). We put in 4' poly pipes, which are well above what is needed to handle the volume of water.
As far as the flood plain, we are outside of the 500 year floodplain, although I do understand that this does not mean that we will not get flooded or get a mudslide come in on us. If that does happen, though, then there will be a bunch of other folks in a far worse condition than us since they are about 25 feet lower in elevation than we are!

 

[herdfan]

</font><font color="blue" class="small">( total foundation, per house was in the neighborhood of 140 yards of concrete for 2,000 sq ft of living area. )</font>

I hope I don't need that much concrete! /forums/images/graemlins/blush.gif /forums/images/graemlins/blush.gif /forums/images/graemlins/blush.gif
That would kinda ruin my foundation budget /forums/images/graemlins/crazy.gif