house pad question for the general populous

[GeorgeG.]

Seems like forever but I've been working on getting enough dirt to build up my house pad. I just spoke with a soils engineer and he suggested something that I haven't done.

To give a little info about the site... the length of the pad is 110ft x 80ft. At the front, it's level on undisturbed soil. The rear has almost 5 feet of back fill that's been run over with a skid steer to build up the first 13 loads of dirt, then I had another 30 loads dumped on top of it, ran over with a skid steer, then end dumps ran over it while dropping another 40 loads, then a bull dozer ran over it to spread the rest. I'm planning to add piers, provided I'm not sitting on water, which I don't think I am.

Long story short, while speaking with the soil engineer, he said they usually recommend digging out the pad site and then building it all back up evenly so that if the soil does settle once the house is built, it's likely to settle evenly.

I've been told that piers is a good investment, especially with the backfill I have. My question is which is better... going with piers or digging it all up and building it up evenly? At this point, I don't know if digging it all up and starting over would be cost effective. The pad is essentially done but the question still remains.

If anyone has any feedback, it would be greatly appreciated.

[8mpg]

I would go with what the engineer recommends. Your concrete guy should have their own engineer who will engineer the slab. The soil engineer should have recommendations of the soil strata from drilling core samples. Whether you need piers or just regular slab on grade will depend the engineer reports

[GeorgeG.]

The soil engineer will get that info. I did ask and he said they get two borings on opposite sides and go 20-25 feet. I told him about the slope and amount of back fill and he said we'll definitely need piers since we didn't dig it out and build it up evenly.

[Baron Von Crowder]

My buddy's house was build 15 years back, and he didnt want to have issues with foundation shift on the black dirt his house is on. The engineer told him to put in piers, and he doubled the amount they required. His house hasnt moved a bit, even though his pool and decking have quite a bit. He only had to drill about 20 feet to bedrock.

[mustang1200]

They dug our pad down then back filled it a 6 to 12 inches at a time while watering and compacting all the way up to the height required. Additionally we have piers every 10 feet under the trenched concrete beams. The piers were drilled to 25 feet for bedrock. Which ever came first.

Here you can see the build up

[ceyko]

I can only speak about my experience so far.

My foundation is post tension with what I consider a lot of piers. (52 or 54, can't remember) The house is 17ish years old and no foundation issues that I can detect, to include doors. That's not to say there is not a hairline here and there, but it's simply hairline - not even "minor" - you have to look for them.

I just got a new neighbor who is a builder for Tony Miller and he opted for piers as well. Additionally a couple other homes have piers with no foundation issues around me. Another neighbor does not have piers and he has moderate foundation issues (in the grand scheme of things, when it's your house - they are huge problems).

Now it may be worth a core sample of sorts, because some places around here have shale not too far under. While other places it's way deep. If you were to have shale under you, you could opt to forego the piers and probably be fine...but likely you should get piers.

Just my experiences/observations - I'm not an expert or trained.

[Blackpony]

We are almost ready to start building in Van alstyne and our builder said he will not build in the area without piers. We asked why. He said that the dirt in the area has such a huge swing in expansion and contraction that not doing piers, will almost guarantee you to have major foundation issues. My neighbor just bought their house about a year and a half ago. It is around 30 years old, they spent over 40k getting the foundation straight and level. The house was not built with piers. This past year all the rain we got completely ruined their foundation again costing them another 18k to fix it all over again. They said the foundation repair company said that this area is terrible when it comes to ground shift and such.

[ceyko]

We are almost ready to start building in Van alstyne and our builder said he will not build in the area without piers. We asked why. He said that the dirt in the area has such a huge swing in expansion and contraction that not doing piers, will almost guarantee you to have major foundation issues. My neighbor just bought their house about a year and a half ago. It is around 30 years old, they spent over 40k getting the foundation straight and level. The house was not built with piers. This past year all the rain we got completely ruined their foundation again costing them another 18k to fix it all over again. They said the foundation repair company said that this area is terrible when it comes to ground shift and such.

The cracks in the ground get back enough you can stick your foot down in them - that's on developed land...etc..etc.

[8mpg]

I think the $1000 in core samples is worth it...

My property where Im hoping to build has already been core sampled. The geotech's report said we have a PVR of 1.5". We have mostly sandy soils between 2 and 8 feet down. Its a blessing. He said I shouldnt ever have foundation problems

[TexasPyro]

By the way, running it over with the skid steer doesn't pack anything down. If that's their typical practice, you might not want them doing your dirt work.

Not necessarily, if the lifts are small enough, compaction is no big deal. If he had tandem dump trucks driving all over his pad that will compact it as well. Most geo's actually call for the lifts to be driven over by a fully loaded tandem dump truck.

The big problem that I see is that they didn't add any water to the lifts as they went up with it. Its impossible to get proper compaction without water. Its impossible to know how much water to add without a geo report. This is probably why the engineer is recommending pulling it out and moisture conditioning it all back in.

Sounds like you already have, but paying for a lab to do soil samples is a must in my opinion, they will tell you the plasticity index of the soil and what your target moisture content should be.

[lowfast]

Get the geotech borings done, worth the cost to know your subsurface conditions. If you can afford the piers go that route, once on piers, if designed correctly, it should not move period.

[Blackpony]

The cracks in the ground get back enough you can stick your foot down in them - that's on developed land...etc..etc.

Yup exactly. And after a small amount of rain, my land is so soft that just stepping leaves about 3-4" deep prints. It's crazy how that stuff works.

[lowfast]

Texas soil pretty much sucks as far as foundations are concerned. We are also building a house out in Grapevine. I went so far as to look into doing a suspended slab on void forms/piers. Try around $23 a square foot, not in the budget, not gonna fly. So now we are looking at slab on grade on piers. If the pad is properly drained, ie water runs away from the slab and you do not have plumbing leaks then most of your foundation issues will stem from the shrinkage from drying. This is where the piers come in, they support he slab if the dirt recedes. At least this is my logic.

Do you know what the PVR of the soil is on your site?

[TexasPyro]

We do have pretty bad soil around here, I recently read a geo for a proposed building in Lewisville that had a PVR of 7"+. That's some expansive stuff!

[lowfast]

Had an Arlington project with a PVR of 16+ Some places here the clay is just crazy. My lot we are getting ready to build on have a PVR between 2 & 3 depending on the boring location.