Can anyone identify this structure please?

[Crystal]

Hello, I’m hoping someone can advise please.

We own a small piece of land opposite our 1920’s home.

When we bought the house we had a lot of top soil brought in to level it off a little bit, grassed it and now use it as a wildlife area.

There is a structure in the field, there are two square manhole covers and there was two concrete areas, one either side.

We never met the owners and there was no one to tell us what these structures are.

There has never been a property on the land.

We suspect they may be water cisterns?

We decided to put soil over the concrete areas, not the metal covers, as the the concrete was quite unsightly. We’ve managed to grow some mossy grass on there, it’s not great quality but hides the concrete.

I’m now wondering if we did the right thing or will the soil perish the concrete?

Are the tanks likely to go under the concrete or just the metal covers?

If the concrete deteriorates could it collapse into a void of sorts?

Thanks for any help.

 

[Flyfisher]

Could it be a septic tank? Ours is quite a long way from the house so absence of an adjacent property might not mean very much.

Have you removed the covers and had a look inside?

As for covering with grass, I would't worry too much about that affecting the concrete. Our septic tank is also covered with grass leaving only the covers visible and the only issue is that in very dry weather the grass above the concrete/brick tends to dry our and turn brown far quicker than the surrounding area because of the very thin layer of earth sustaining the grass, thus revealing the underlying structure.

 

[stuart45]

I think it could be a septic tank as well. The older ones were often brick built with a reinforced concrete slab on top.

 

[Kearn]

Water cisterns need to be fed from grey runoff or similar, and also usefully enough located to reuse. These don’t appear to tick either box.

Grass really shouldn’t be damaging concrete! But yes, the concrete will be the top of whatever void is under, the inspection hatches are just that.

The best person to answer your question is someone with a touch and camera, once the inspections hatches are lifted…

 

[Cubist]

I would suggest you don't bury those steel covers. It's not clear from the photos but the thinner pressed steel covers can rust rapidly while the cast iron/steel variety can fracture. Both, or rather whatever they hide, can become a hazard to animals and people.

 

[Flyfisher]

Agreed, especially if it is a septic tank and likely to be emptied by heavy machinery (eg large tractor & vacuum tanker) that might drive over and break a hidden cover. You can probably guess how I know about that risk and why I know that manhole covers have various weight-ratings depending on what traffic they're likely to encounter, from pedestrian only up to aircraft runways. A search for 'BS EN 124' will reveal all (and probably cure a bout of insomnia as well).

 

[paulc]

I think it could be a septic tank as well. The older ones were often brick built with a reinforced concrete slab on top.

Whilst it is most likely a septic tank, it is just possible there is a bunker under the covers.
Quite a few of the properties in this area have mystery concrete slabs in their gardens. Some cover old septic tanks, but a few are air raid shelters dating from WWII.

 

[Crystal]

Agreed, especially if it is a septic tank and likely to be emptied by heavy machinery (eg large tractor & vacuum tanker) that might drive over and break a hidden cover. You can probably guess how I know about that risk and why I know that manhole covers have various weight-ratings depending on what traffic they're likely to encounter, from pedestrian only up to aircraft runways. A search for 'BS EN 124' will reveal all (and probably cure a bout of insomnia as well).

Hello, thank you for your reply.

We haven’t and would never cover the metal manhole covers. We have covered the concrete parts with soil, in some places about an inch thick, some slightly more and put some grass seed on.

Do you think in your experience this will cause the concrete to perish and possible collapse?

This is completely fenced off private property, no vehicles drive on here.

And if it’s a septic tank, it’s unused and has likely never been used.

Thanks again for your help.

 

[Crystal]

I would suggest you don't bury those steel covers. It's not clear from the photos but the thinner pressed steel covers can rust rapidly while the cast iron/steel variety can fracture. Both, or rather whatever they hide, can become a hazard to animals and people.

Thank you for your reply.

The metal covers are not covered and we would never do this.

Just the concrete areas which are at either end have been covered with a thin layer of soil, around an inch thick and grass seed.

I was concerned about the concrete perishing under the soil and collapsing if it’s a void under there.

My husband thinks I’m overthink this.

 

[stuart45]

In general soils don't cause damage to concrete, otherwise concrete wouldn't be used for foundations.
However, in certain subsoils sulphate resisting cement is used where an extremely high content of sulphates are present.

 

[Crystal]

In general soils don't cause damage to concrete, otherwise concrete wouldn't be used for foundations.
However, in certain subsoils sulphate resisting cement is used where an extremely high content of sulphates are present.

Thank you, that’s reassuring to hear. I’m one of life’s over thinkers unfortunately. Not always a great combination with an older property.

 

[Gothichome]

I agree with the others, most probably a septic tank. Most have two sections the solids settle out in the infill section and the liquids flow into the second tank. Each will have a lid to allow the tanks to be cleaned out. You may also have (most probable) a weeping field in the general area of the tank. This allows liquids to be spread out into the surrounding soils. These fields are porous pipes emanating from the septic tank (usually a a couple feet below the lid) these can be damaged by heavy equipment driving over them or digger operators not being aware they are there.