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Mine Exploration Forum

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Author Finding a buried manhole.
stuey

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Joined: 15/08/2007

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Finding a buried manhole.
Posted: 21/07/2010 17:51:50
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Totally off topic, I am looking for a buried manhole. It is under up to 40cm of rock/mud/dirt.

My crappy metal detector cannot get further than 6" and faced with a similar situation, I wonder what you lot would do.

Digging the whole garden up is not an option.

IP: 87.114.16.231
lawsonium

Joined: 30/12/2007
Location: Wales - generally (poor house)

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Finding a buried manhole.
Posted: 21/07/2010 18:09:14
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Any documents with the deeds to the property detailing the run of service mains? Might narrow your search down and make a dig more productive.

Failing that, search for manholes in the area which could link up and try to work out the line of the pipes/drains to see if you can zero in on it. Using drain rods can help you work out distances though this is difficult if the pipes have any bends in them.

Drastic measure could be:
Split area you think it is in into a metre squared grid.
Get a long thin (inch maximum) but blunt metal bar and 'tap' it through the debris 3 or 4 times in each square until you hit metal. This is risky especially if you are dealing with terracotta pipes.

You have probably thought of these already so I'll keep thinking.

Good luck, let us know how you get on.

--

Nom nom nom.
IP: 92.16.223.119 Edited: 21/07/2010 18:10:46 by lawsonium
stuey

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Finding a buried manhole.
Posted: 21/07/2010 18:11:28
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There aren't any pipes or plans. Just a manhole over a stone pipe. I also can't get up the stone pipe or even get a camera up it.

Edit, I know the manhole is a big piece of iron.

IP: 87.114.16.231 Edited: 21/07/2010 18:12:02 by stuey
Tamarmole

Joined: 20/05/2009
Location: Tamar Valley

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Finding a buried manhole.
Posted: 21/07/2010 18:11:52
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Dowsing??? IP: 86.148.14.98
stuey

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Finding a buried manhole.
Posted: 21/07/2010 18:22:01
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Dowsing isn't something I have tried or am any good at. IP: 87.114.16.231
Gwyn

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Joined: 23/10/2007
Location: Bethesda.

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Finding a buried manhole.
Posted: 21/07/2010 18:23:11
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Compass deflection? IP: 92.8.205.49
stuey

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Finding a buried manhole.
Posted: 21/07/2010 18:24:25
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Gwyn wrote:

Compass deflection?


Elaborate........

Would this be a significant with such a small chunk of "stuff"
IP: 87.114.16.231
lawsonium

Joined: 30/12/2007
Location: Wales - generally (poor house)

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Finding a buried manhole.
Posted: 21/07/2010 18:41:45
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Dowsing isn't going to work.

The only efficient way to dig (it's only 40cm right?) is like archaeologists do, in narrow trenches that intersect the area in question.
Hopefully you will intersect a pipe or other clue and you can zero in on it.

It might be a bit of a pain but you're almost sure certain to find it (If it is indeed there at all!!! lol)

Other than that, hire a powerful metal detector.

--

Nom nom nom.
IP: 92.16.223.119 Edited: 21/07/2010 18:43:09 by lawsonium
Tezarchaeon

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Finding a buried manhole.
Posted: 21/07/2010 18:57:24
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Have you not got a long pointy ended pole you can jab around with in the ground? Something like a spade handle with a pointed end prehaps. You'd feel the bang soon enough. Also look for slight depressions in the ground or grass decolouration. IP: 95.149.154.74
Gwyn

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Finding a buried manhole.
Posted: 21/07/2010 19:12:14
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A man hole lid is quite a significant magnetic anomaly lump!
I've just been trying the technique, on a cast iron man hole assembly, with Suunto M3 and a Glausner Mk.4 and getting significant deflection from about 25cms. Not sure if it'll work with a lump of cast iron buried at 40cms. but it might be worth a try using two compasses on transects.
Just an idea!
IP: 92.8.205.49
Peter Burgess

Joined: 01/07/2008
Location: Merstham. Or is it Godstone ...... ?

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Finding a buried manhole.
Posted: 21/07/2010 20:26:05
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If it is a cast iron lid and not a flimsy thin steel cover, then a Suunto compass will be deflected by it. Perhaps by only a degree or so, so you would need to know what you were doing. It would take a long time as well, as the deflection will only be significant when you are really close, and probably on the ground to boot. When surveying the mines in Surrey we had to be conscious of manhole covers, and buried plate rails. The effect was noticed by the difference between fore and back bearings. Of course we knew where the lids/rails were and you don't. So how you go about detecting the lid is a challenge. But I think the lid will affect a compass and therefore you may have a way forward. If you want to see what effect to expect, go and find an exposed cover and experiment. But be aware that there MIGHT be more iron or steel below any cover you experiment on which would increase the deflection a bit.


--

Hé ! Ki kapcsolva le a villanyt ?
IP: 92.0.32.102
ian S

Joined: 20/11/2007
Location: just outside of Consett

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Finding a buried manhole.
Posted: 21/07/2010 20:35:17
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I drive a 2 meter roadplaning machine for a living and i find the damn things all the time Cursing

--

I am a mole and i live in a hole !
IP: 89.240.96.90
stuey

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Finding a buried manhole.
Posted: 21/07/2010 20:47:10
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Banging spikes in isn't an option due to rocks (and hard rocks) packed with gravel.

We've tried picking it, but it's just too much of an area and there are no indications whatsoever which single out any piece of ground.

It has to be some sort of metal detector or pipe finder.

Digging everything up is not an option.
IP: 87.112.143.147
lawsonium

Joined: 30/12/2007
Location: Wales - generally (poor house)

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Finding a buried manhole.
Posted: 21/07/2010 20:49:56
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I think you've answered your own question there. Get on the blower tomorrow to some hire shops.
The service guys use those big yellow hand held cable and pipe finders and I think they work down to depths of several feet and through tarmac.

--

Nom nom nom.
IP: 217.171.129.70 Edited: 21/07/2010 20:51:44 by lawsonium
stuey

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Finding a buried manhole.
Posted: 21/07/2010 21:12:14
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This sounds good. I was wondering whether they only worked for electricity.

Question 2.

Has anyone used a pipe finder?


IP: 87.112.143.147
lawsonium

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Location: Wales - generally (poor house)

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Finding a buried manhole.
Posted: 21/07/2010 21:14:25
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Turn the dial to 'metal', point it at the ground and walk back and forth till it beeps Smile

--

Nom nom nom.
IP: 217.171.129.70
Gwyn

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Joined: 23/10/2007
Location: Bethesda.

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Finding a buried manhole.
Posted: 21/07/2010 21:34:48
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I suspect that Lawsonium has the answer!
I've been hunting high and low for my stud/cable/rebar detector so I could test it on some man holes...but I've been unable to locate it!
What are the big, yellow, hand-held cable and pipe finders called?
Please let us know how you get on Stuey. Good luck!
IP: 92.8.205.49
loomis

Joined: 27/10/2009

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Finding a buried manhole.
Posted: 21/07/2010 21:48:32
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It's called a CAT and JENNY. The CAT stands for Cable Avoiding Tool. I first used one around years ago while working for British Gas. They locate metal covers, electricity cables, and telecom equipment etc. and by using the induction setting can follow any metallic cable or pipe IP: 86.16.11.51
Morlock

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Joined: 31/07/2008

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Finding a buried manhole.
Posted: 21/07/2010 22:59:26
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loomis wrote:

It's called a CAT and JENNY. The CAT stands for Cable Avoiding Tool. I first used one around years ago while working for British Gas. They locate metal covers, electricity cables, and telecom equipment etc. and by using the induction setting can follow any metallic cable or pipe


Yep, great bit of kit. Whilst checking for a new build house I found a buried manhole (heavy cast iron) and a 6 inch steel methane pipe from the local pit to the gas grid, found the pipe on the radio frequency setting!
IP: 86.27.3.13 Edited: 21/07/2010 23:00:11 by Morlock
Digit

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Joined: 29/07/2009
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Finding a buried manhole.
Posted: 22/07/2010 07:22:26
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If the ground is soft enough probing with an iron (or iron tiipped) rod should work. The 'feel' and sound of iron hitting iron is different to iron hitting rock orthe odd half brick. Rod needs to be about 3/8" - 1/2" diameter. Cheep, siimple and effective.

--

If you keep your eyes open you may see something interesting. If you don't something interesting will find you.
IP: 81.178.3.180
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