Totally Mystified

[Jim Gecz]

I have been in many crawl spaces but have never seen anything like this. 1959 split level home with two separate crawl spaces.

You enter the first crawl space under the raised living/dining rooms and kitchen area. Poured concrete foundation and wood framed floor structure. You can then crawl down a few feet into this world of wonder under the other half of the house and garage, which traditionally in a split would be a slab.

It is a slab, but it is a floating slab! No wood framing anywhere. All concrete and rebar raised on foundation walls and columns.

In the first and second photos you can see the remnants of the wood forms used along the footing of the foundation. Notice the aggregate bottom of the floor? It is uneven, so no forms were used there. How the heck??

In the second photo you can see the HUGE voids that have formed all around the crawl space under the foundation walls and the footings of the columns.

Obviously I called these voids out, but I am mystified as to what type construction this is, and how did they get those floors in place?? Some sections still had a thin clear plastic wrap on them, but by the uneven bottom there is no way any forms were once in place. Is there???

Any ideas how this was done?

321963219432195

[Steve Payson]

Typically a slab is poured over a 4" bed of gravel covered with plastic (undisturbed soil, then gravel, then plastic, then concrete). Look at the remnants of plastic, you see the impressions (or depressions) caused by the weight of the concrete against what was once the layer of gravel.

Looks as if someone excavated but seems like a lot of work just to run new utilities. Either way, there are some serious issues there.

[BARRY ADAIR]

appears to be similar to tilt wall construction...left in place

they probably had forms installed
laid the poly & gravel/aggregate atop so concrete wouldn't bond to the forms
removed what forms that hadn't bonded and left the rest for you to discover at a later date

[Jim Gecz]

Someone suggested it may have been hydro-blasted.

Felt like I was spelunking.

[Mark Reinmiller]

Its hard to tell from the photos, but I have seen similar issues before. In many cases soil fill below slabs will settle leaving voids. They are not usually that large. In the one case I have seen the soil did settle 3-4 feet below the slab. This was a case where houses were built over an old quarry. The foundations were on pilings, but not the slab. I have seen slabs with no reinforcing other that welded wire fabric span distance of 14 feet without failing (but did sag several inches).

If that is not the case and the bottom of the slab is very rough, then it is possible that someone excavated after the slab was poured.

I have concerns with the foundation photos, but could not see clearly enough. Post more photos if you have them.

[Jim Gecz]

...
I have concerns with the foundation photos, but could not see clearly enough. Post more photos if you have them.

Not sure if these are any better, but here goes. Thanks!

[Mark Reinmiller]

If anyone planned to do this ahead of time with the idea that they would excavate why would they bother with crushed stone?

I'm not sure what I am looking at in the third photo. That is the one that concerns me the most.

As to whether the unsupported slab is structurally sound, reinforced slabs are common, but not constructed this way. This looks more like a DIY mess.

[Raymond Wand]

Can't speak as to how or why as per the construction, but appears water has been the culprit in the subsidence/washouts and deterioration of remaining wood forms.

[Jim Gecz]

If anyone planned to do this ahead of time with the idea that they would excavate why would they bother with crushed stone?

I'm not sure what I am looking at in the third photo. That is the one that concerns me the most.

As to whether the unsupported slab is structurally sound, reinforced slabs are common, but not constructed this way. This looks more like a DIY mess.

The third photo shows the bottom of the foundation footing with some rotted woods forms. The black along the bottom are large voids, some with standing water.

[Jerry Peck]

Not sure if these are any better, but here goes. Thanks!

I see what looks to be a good sized crack at the right side of the 4th of 4 photos.

It almost looks like someone shot wet concrete with large aggregate on the slab and beams/girders - not sure why as that is not the typical gunite mix used to repair concrete beams and slabs ... the other logical explanation for the rough aggregate look is illogical (because the soil would have to subside all that distance, yet the sides of the grade beams do not look like the soil subsided down them over the years ... weird - definitely.

[Raymond Wand]

Are those insulated pipes potable water lines? Could they have frozen and leaked for sometime?
High water table, intermittent spring, house situated on side of hill?

What is the explanation from the vendor?

[Jim Gecz]

Are those insulated pipes potable water lines? Could they have frozen and leaked for sometime?
High water table, intermittent spring, house situated on side of hill?

What is the explanation from the vendor?

House is in foreclosure, but actively lived in, no leaks, and flat yard. High water table in the area, yes. Woman who owns it spoke broken English and had no clue about anything.

So that made two of us - well except I was smart enough to know big black holes with water were wrong when I saw it.

[Mark Reinmiller]

Where in NJ is the house located? I would bet that the footings are on pilings.

[Jim Gecz]

Where in NJ is the house located? I would bet that the footings are on pilings.

Wharton, NJ Never have seen pilings used anywhere in this area. Not like the Jersey shore area.
I may take a ride to the building department and see what i can dig up.

Thanks to everyone with their input!

[Jerry Peck]

I would bet that the footings are on pilings.

You mean such as grade beams and piling caps ... that would account for the soil subsidence without and settlement.

Many homes in South Florida which are built along the Intracoastal Waterway and along the beaches are built on pilings with grade beams and piling caps.

I have seen a foot or more soil subsidence at those, one I inspected had the concrete drive 8" lower than the entry to the garage ... kind of difficult to make it into the garage with the car ... :)

[wayne soper]

Seen it many times!! always the same. In my neck of the woods they took telephone poles and drove them into the mud, built up the ground level and poured the slab on top of the poles, excavating out after. Crawling into those mud pits was just wonderful and I am glad to say, not one of my clients bought one of those pieces of crap. Just ridculous building practices usually used in wetlands or filled areas so check out a wetlands map for more info.
It doen't matter what else is wrong down there. That is a POS

[Jerry Peck]

Seen it many times!! always the same. In my neck of the woods they took telephone poles and drove them into the mud, built up the ground level and poured the slab on top of the poles, excavating out after.

Wayne,

Do you know if those slabs were poured with reinforcing in them, or just as 'slabs on fill'?

If the slabs are structural with proper reinforcing in them, no problem regarding the slab no longer being on fill. If the slabs were not reinforced, then that would be a big problem as the slab was not designed to be self-supporting.

Just curious if you know or not.

That practice would account for the bottom of the slabs being the way they are (not smooth like they would be if poured on forms).

[Terry Beck]

I have seen one older home that was originally slab-on-grade where the dirt under the slab was later partially excavated to allow for some plumbing repairs (rather than tearing up the concrete floor). But the amount of excavation was NOwhere near this. I saw another home where an addition was built over a previous patio, leaving a void between the patio and sub floor (but that was not a concrete subfloor), and then plumbing lines added later. You have an amazing mystery here.

Does it look like the plumbing was added after the fact? The water supply and waste pipes do not look like there were previously buried. What does the slab look like where the plumbing lines pass up into the level above the floor? Does it look like the holes were drilled through after the slab was poured, possibly leaving rough beveled edges around the hole? What does the plumbing look like in other parts of the house?

[John Kogel]

Hopefully your clients are having second thoughts about that place.

[wayne soper]

Wayne,

Do you know if those slabs were poured with reinforcing in them, or just as 'slabs on fill'?

If the slabs are structural with proper reinforcing in them, no problem regarding the slab no longer being on fill. If the slabs were not reinforced, then that would be a big problem as the slab was not designed to be self-supporting.

Just curious if you know or not.

That practice would account for the bottom of the slabs being the way they are (not smooth like they would be if poured on forms).

Jerry ,I believe they were. I never saw one that had any type of cracking or breakage that would ocurr without. And yes, that why all the gravel at the bottom.
There were none thatwere left in the dirt.

[Thom Huggett]

It doesn't appear excavated after-the-fact to me. Are the floors above sagging or settling? If not I would say that the house was designed with an elevated slab floor on a pier and grade beam foundation. It may have been done that way due to the presence of expansive soils. I wouldn't be concerned unless there are signs of distress. The old wood form boards should be removed and an underfloor drainage system should be installed, however.

[Steve Payson]

It doesn't appear excavated after-the-fact to me. I would say that the house was designed with an elevated slab floor on a pier and grade beam foundation.

So how do you think the slab was poured?

[Rich Goeken]

Hopefully your clients are having second thoughts about that place.
Was this caused by a closed mine?

[Vern Heiler]

Looks like the house was relocated (moved) to me.

[Vern Heiler]

Hopefully your clients are having second thoughts about that place.
I'm amazed at how well the hole followed the paint line:D.

[ROBERT YOUNG]

Hopefully your clients are having second thoughts about that place.
Be positive.
Sell the hole as a start to an inground swimming pool.;)

[John Kogel]

Was this caused by a closed mine?That was just a pic I pulled off the net. Sink hole, usually due to a karst formation, limestone cave, that collapsed.


Looks like the house was relocated (moved) to me.Hey Vern, how's the sciatica now? Better, we hope.

The OP house - slab-on-grade with an attached garage slab, not something that can be jacked up and moved. If it was moved, I-beams would have been slipped under the slab. Look at the 3rd pic in the last batch Jim posted. It shows clearly that the ground has sunk away from under the foundation.