How to build on "junk fill"?

Question

I recently purchased a vacant residential lot on which there was previously a single family home that was foreclosed on and then demolished. The house had "sinking" issues which rendered it unsafe. Supposedly about 100 years ago they dug a test pit looking for iron ore. When they didn't find any, the pit was then used as a dump for construction debris and then covered over.

I just got a hold of the geo-engineering report ordered by the Township, complete with borings, which basically says that there's uncompacted, junk fill down to 30 feet, with bedrock at 45-65 feet.

What is the best approach for building on a lot such as this? The geo report mentions replacing the fill and properly compacting it. The lot is 14,000sq/ft, so I'd imagine that would be a big to-do, unless only the soil under the house footprint would need replaced. I've been reading up on helical piers and am wondering if that may be an option.

I'll be talking to some experts in the coming weeks, but I'd like to get some education from BPers before I do.

Mark Beekman · Answer

Great minds think alike, Justin! I just started looking into mobile homes and possibly a "tiny house" that I can put on Air B&B. A mobile home can be put on the lot, but they still require a slab of sorts to tether it to.

Justin Fox · Answer

Is it restricted?  Could you slap a couple mobile homes one it?  I know that's probably less desirable but you'd make some money.

Justin

Mark Beekman · Answer

I'd have to write a book to answer that question. The VERY short version is that I didn't know about the issues, despite attempted due diligence. The Township wouldn't answer my questions and claimed to not have any documentation pertaining to the previous house demo or soil/fill issues. I was then informed by neighbors and threatened legal action and then all of a sudden they "found" records.

It was also so cheap that I couldn't resist.

Wayne Brooks · Answer

Helical piers need to be installed in sound soils.  As far as I know, you can't install in rock though.  Here there would be either excavate and replace, yes a big to do, or drilling/installing concrete pilings (square 8-12") but then that means "beam" foundation construction, on the piers.

Justin Fox · Answer

@Mark Beekman

I wonder if you could get away with doing a load of slag or crushed concrete instead.  I know they use mobile home tie-downs on carports and those don't typically have slabs.

Justin

Manolo D. · Answer

@Mark Beekman Too expensive, yes. Imagine putting a pencil on a sandbox and remove the sides on it, one side sand is 6" and another 1-2", it will eventually fail. The only process where piers work is if they have the same pressure on all sides. Right now, I would imagine your sandbox at 2" of sand with a pencil sticking up. It depends on how good your structural engineer is, you might need more than 1 opinion as different people have different solutions, and what you're going to do might cost a lot, it may vary a couple of thousand, if not tens.

Jay Hinrichs · Answer

@Mark Beekman  I just had this happen to me in Portland.. we were going through land planning and it was announced that the neighboring lot had some old fill issues so now we want you to do borings etc.  hopefully its nothing that can't be mitigated reasonably.. but like you are in the dirt right so really no matter the fix it pencils.. but had we paid the full price crazy market prices that PDX is now enjoying this would be a super bummer... its not normal for us to have a geo look at flat lots here in PDX ... hillsides with 20 to 40 degree slopes sure.. but not flat lots in the inner city.

Mark Beekman · Answer

And would the replacement of fill option require replacement of fill for the whole lot, or just the building area?

Mark Beekman · Answer

Why don't you think piles to bedrock won't work? Too expensive for this application?

What do you think about a mat foundation?

Manolo D. · Answer

@Mark Beekman There's a bottom line to what you are trying to do, it will be too expensive. 10 yards x 1500 sq yards equates to 15k cubic yards, thats too many dumptrucks to count. Helical piers won't work. some kind of spread footing with pier to bed rock might work but I do not believe it's feasible, it's something we use for bridges.

How to build on "junk fill"?

Most Popular Reply