Diagnose a sink hole ?

[Externet]

Hi.

Bought a property. It has a 1m diameter, 1m deep sinkhole by the front yard, 5m from the house. The concrete block foundation shows zero signs from being affected, not even a hairline crack anywhere.

Neighbors from the area say it has always been like that. That when filled by previous owners, very slowly soil caves in. Do not know what 'very slowly' means. Guessing, takes a year or two to need refilling with dirt.

 

There is a confirmed no relation with a mains water leak. Sewer lines are distant and PVC. No foul smells emanate.

Terrain is very high in relation with the rest of the neighborhood. Could be said there is very little higher terrain around, but there is some.

 

Bottom of pit shows smoothed gravelish look, like water flowed. There is never water every time I checked. Previous owners are not available. Municipality has no maps, clues, reports, build permits blueprints nor help.

 

There is a chance a roof downspout into ground PVC piping with no discernible underground path has something to do with it, by my suspicion. The downspout enters the soil 7 metres away into a pipe. There is no signs of any pipe in the pit. There is no signs of that pipe exiting/surfacing anywhere.

 

What would you suggest to do ?

 

What would be a method to trace at the surface the path of the downspout drain ?

What would happen if someone pours Portland cement in the sink hole ?

 

Thanks.

 

Edited - added: Just thought of... ¿would it make sense to pour water in the downspout pipe entering the soil and monitor the bottom of the pit ? Have not inspected such while raining... Or, any clever action on your mind ?

Edited December 2, 2016 by Externet

[DrKrettin]

My first step would be to excavate around where the downpipe drain goes underground. It shouldn't be too difficult to find the elbow which tells you which direction it runs off at. I would be tempted to dig a trench along the line of that drain and find out what provision there is to lose the water. Until you've done that, I can't see much point in suggesting anything else.

[dimreepr]

You could get a ground-penetrating radar survey.

[Endy0816]

How common are sinkholes in the area?

[Externet]

Thanks, gentlemen.

Not a common ocurrence in the area. Ground is concrete paved at the area that excavation would be convenient to inspect.

[michel123456]

Maybe it is an ancient unused cesspit. https://en.wikipedia.org/wiki/Cesspit

[John Cuthber]

"Hi.

Bought a property. It has a 1m diameter, 1m deep sinkhole by the front yard, 5m from the house. "

Why?

[arc]

I've got a few questions;

 

1. How far is the sink hole from the street.

2. Does the street have curbs and storm drains.

3. Is this neighborhood older than thirty years.

 

Years ago I purchased a fixer-upper built in 1920 that had been hooked up to the district sewer in the late 1950's or early 60's. The line ran down the side of the house from the street. The surface above it had been a graveled driveway before and after the installation of the line. The driveway had been slowly raised with added fill material over the years by the previous owner and I had assumed it was to prevent the surface water from the street coming onto the driveway. In preparation for paving the driveway I remove around 30 cm of material and continued to drive on the area.

 

One day I pulled onto the driveway in my Toyota Corolla, pressed on the brakes and felt the whole left side of the car drop to the ground as if the wheels had fallen off. I had collapsed the surface into the old ditch. I had just enough clearance to back out and examine the results. I could see where the original fill material had settled approximately 30cm, leaving a dome shaped cavity running the entire length.

 

Some properties have easements that the local water dept use. Some of these service lines are quite large. The ditches are usually back filled with crushed rock to inhibit corrosion and prevent post burial settling of the over laying and under laying fill material. Fill material will settle even after the compaction done during the installation work. Older lines did not get as good of compaction as the more recent installations do. Mechanical and hydraulic machinery have greatly improved the process.

 

Its possible these cavities could provide a place for surface materials to migrate into over extended periods of time. I think its time to do some testing of the site. Can you probe the area with a small diameter rod to see if a hollow area exists there or adjacent to it?

[Externet]

Thanks, arc.

I've got a few questions;

 

1. How far is the sink hole from the street.

2. Does the street have curbs and storm drains.

3. Is this neighborhood older than thirty years.

 

...Can you probe the area with a small diameter rod to see if a hollow area exists there or adjacent to it?

1. 8 metres from the paved street.

2. Curbs, yes. Being not flat terrain, there is no storm drains nearby until a couple of blocks downslope as rain does not puddle at all.

3. Neighborhood is from the seventies, house was built in 1996 (20 years new)

 

Sinkhole terrain is 0.7m above the street level. Water at the street does not enter the yard. Its the reverse.

 

Not a soft enough soil to probe. County topographical maps show no sink holes in the area. In three days I will have utilities demarked and a friend will come with digging equipment to explore. Will try to add a picture later.

Edited December 3, 2016 by Externet

[arc]

Thanks, arc.

 

Not a soft enough soil to probe. County topographical maps show no sink holes in the area. In three days I will have utilities demarked and a friend will come with digging equipment to explore. Will try to add a picture later.

 

Your welcome. I look forward to seeing what you find. Digging a hole in the ground and looking at the night sky with a telescope are the only two "Time Machines" that anyone can own and operate.

[Externet]

The nearest corner of the house has the suspect downspout; there is another at the corner in front of the vehicle, inspected its pipe inside and that one on front of the vehicle bends/aims towards the one by the back of the vehicle;

The broom shows in the hole. The snake did not do it.

I just disconnected both downspout bottoms to let it flow onto the paved driveway/soil surface to evaluate the hole after rain...

 

 

 

Edited December 3, 2016 by Externet