Locating a man made tunnel

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Kknq
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Locating a man made tunnel

Post by Kknq »

Hello everyone,

First and foremost, I am sorry if this is categorized as Off Topic, but while I was searching through this forum, I saw several similiar questions so it seems that its not against the rules?

Anyway, while you are already here heres a little of backstory on my matter. My great-grandfather used to be a Hajduk during the first world war in Serbia. He led a small group of men during the uprising and first world war. Fast forward he died in 1999 leaving me with a few clues that he actually hid something on his property. A tunnel made with brick walls, leading to a larger room to be exact. For years I've been trying to locate the tunnel and the entrance with several different devices, unfortunately without any luck.

Over the years and through different clues (old house maps) we were able to locate the tunnel to an area of about 10m x 10m or 30 foot by 30 foot. The entrance measures about 3ft by 3ft and stairs lead further down. The tunnel itself should be about 2.5 foot wide and about 6 foot deep. The main room measures about 7ft x 7ft and is about 6 to 9 foot deep. The soil conditions are 3-5 ft normal soil and everything underneath it, is bedrock(gabbro) with some quartz, so relatively mineralized.

Me and my dad are one step away from actually purchasing a Ground Penetrating Radar since we could use the device in some way anyway (my dad owns a construction company). But after reading alot of reviews on the device I figured that operating such a system is very complicated and could leave me with images with alot of noise and no results. But on the other hand, such features in said conditions should be very clear on the collected data.

So I am asking you guys, is there any better approach at this or would you stick to actually purchasing the GPR and attending courses to get a hang on how to use it? Renting is no option since I searched for months a company with a GPR and there are literally zero companies nearby. The next one would inclued a 10h drive.

Further I researched for months which device would suite me the best for my budget and I found the following devices:

MALA 3XM with a 350MHz antenna
IDS Opera DUO
LMX200 (Sensor and software)
GSSI 3000 with a 400MHz antenna
RD1500

So what do you guys suggest me to do?

TLDR; Trying to locate a manmade tunne with brick walls. Its 6ft deep and measures 2.5ft wide. The ground consists of a 3-5ft deep layer of soil (earth) and everything underneath it, is gabbro with quartz.

Any help would mean alot to us, even if its only shared experiences using the GPR in same conditions or recommondation on the listed devices.

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Re: Locating a man made tunnel

Post by geophix »

Since you are looking for a relatively large target, I would suggest you choose a GPR with lowest frequency to achieve maximum penetration depth. The GPRs you listed are very similar to each other and I don't think you need worry too much about the resolution for your target. So just choose the one with the lowest frequency. There are even better ones available now using fast stacking technology, but I guess they might be a little more expensive.

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Re: Locating a man made tunnel

Post by GuyM »

Maybe think about a high resolution gravity survey?

You are dealing with a shallow "anomaly" and the density contrast between rock and air is pretty big. A friend who did geophysics at Imperial Collge London told me they used to map the boundary of an underground carpark (under a park) in London this way as a field exercise.

A 7' x 7' x 9' void is 441 cubic feet of "missing" rock. If you don't mind being a bit public with this you may be able to get the local University to turn out with their gear and do a few high resolution profile lines....

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Re: Locating a man made tunnel

Post by geophix »

Electromagnetic mapping (measuring ground conductivity) could be another way to find what you are looking for depending on the soil conditions.

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Re: Locating a man made tunnel

Post by Kknq »

geophix wrote:
Mon Mar 02, 2020 12:03 pm
Since you are looking for a relatively large target, I would suggest you choose a GPR with lowest frequency to achieve maximum penetration depth. The GPRs you listed are very similar to each other and I don't think you need worry too much about the resolution for your target. So just choose the one with the lowest frequency. There are even better ones available now using fast stacking technology, but I guess they might be a little more expensive.
Thank you for the sincere respond, do you think it would be "easy" for someone without much experience to read the data? I analyzed nearly all of Data thats available on the net of similiar targets but again thats not comparable to real life experience. I am just scared that I wont interpret the data right.

A good thing is the conditions are somehow good, the ground is flat and there are no objects around it to cause noise. Its literally in the middle of nowhere on a field.

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Re: Locating a man made tunnel

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GuyM wrote:
Mon Mar 02, 2020 4:54 pm
Maybe think about a high resolution gravity survey?

You are dealing with a shallow "anomaly" and the density contrast between rock and air is pretty big. A friend who did geophysics at Imperial Collge London told me they used to map the boundary of an underground carpark (under a park) in London this way as a field exercise.

A 7' x 7' x 9' void is 441 cubic feet of "missing" rock. If you don't mind being a bit public with this you may be able to get the local University to turn out with their gear and do a few high resolution profile lines....
Thank you for the answer, I ll have a look at this method since I am not familiar with it. But it seems that this would also be a really good approach to locate the target.

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Re: Locating a man made tunnel

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geophix wrote:
Tue Mar 03, 2020 5:25 pm
Electromagnetic mapping (measuring ground conductivity) could be another way to find what you are looking for depending on the soil conditions.
We are actually also considering this method, just looking for a good device.

Thanks for the response!

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Re: Locating a man made tunnel

Post by Kknq »

Has anyone ever worked with RD1500? Would you rather choose the Easy Locator PRO HDR or RD1500? Thanks for any help in advance!

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Re: Locating a man made tunnel

Post by jalfer »

Hi,

Recently I did a project where we located basements extents underneath the pavement. Some of them had a "convex" ceiling and was easy to find it (see picture Image) but the ones with flat ceiling were more difficult.

As somebody said, an electromagnetical survey might work as well. We have also located a culvert using that technique. To have more chances, we introduced 2 utility sondes from the outlet so the EM catches the cable easier (the outlet was visible but inside the culvert, there were even roots from trees near to the culvert). The problem with this technique is that you can not know the depth.

Keep us up to date with your plan/site work

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Re: Locating a man made tunnel

Post by geophix »

Kknq wrote:
Thu Mar 05, 2020 6:23 pm
Has anyone ever worked with RD1500? Would you rather choose the Easy Locator PRO HDR or RD1500? Thanks for any help in advance!
I would expect the penetration depths of RD1500 and Mala Easy Locator Pro HDR are very similar. The antenna frequency of RD1500 is 250MHz, lower than Mala's GPR; but Mala's GPR has the HDR technology (fast stacking as I mentioned before) to improve the signal/noise ratio, hence increase the penetration depth. I think the Mala WideRange HDR might be a better choice, it has better penetration depth (and resolution) and it's good for locating underground utilities if you want to keep it for your construction business. It has two antennas with 160 MHz and 670 MHz center frequencies, and it has the HDR technology, too.

Also, if you worry about data interpretation, you can post the data here and we might be able to help you to understand it.

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Re: Locating a man made tunnel

Post by 99thpercentile »

Since it appears that you have more time than money, the target is relatively shallow, and relatively large versus the depth I would suggest electrical resistivity tomography. The DUOYI DY4300B 4-Terminal Earth Ground Resistance and Soil Resistivity Meter costs just over $300 USD for a kit with a resistivity meter, cables, and four electrodes. I would lay out a measuring tape perpendicular to the expected tunnel path and somewhere in the middle of search area. The electrode spacing will be 1 m, so put flags at each m mark along the tape. Since this will be an electrical resistivity tomography (ERT), which is a combination of a resistivity profile and a resistivity sounding, it will take a little while to collect each line. You will be using a dipole-dipole array for this particular data collection.

https://www.dyinstrument.com/duoyi/?q=e ... er/DY4300B

For the first profile you will use a 1 m “a” spacing. Put the electrodes at 0, 1, 2, and 3 m. Make a measurement and record the value. Then move the second two electrodes from 2 and 3 to 3 and 4 m, and make the next measurement. The first two electrodes are current electrodes (A & B), while the last two electrodes are the voltage potential electrodes (M & N). You will repeat this process until you get to the line.

All of your data will be entered into a spreadsheet for analysis. The tunnel may show up in just the pseudo section (plot of apparent resistivity versus approximate depth). If it doesn’t then the next step would be geophysical inversion. The standard software for this is RES2DINV, which is probably out of your budget, so you might have to use something free like boundless electrical resistivity tomography (BERT).

http://resistivity.net/bert/

I have only done this approach once to map out an escape tunnel from the world’s largest prison in Iraq. It was painfully slow, but it worked. The only reason I did it was that a former colleague insisted that I didn’t need the switching resistivity system, but once on site the base commander really wanted us to verify the tunnel location. It took three days to do a survey that would have taken a few hours with an automatic switching system.

Good luck, let me know if you have any questions.
Attachments
Image of manual ERT survey for tunnel detection.
Image of manual ERT survey for tunnel detection.
Ryan E. North, PhD, RPG, GISP
Principal Geophysicist
ISC Geoscience
ryan.e.north@iscgeoscience.com

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Re: Locating a man made tunnel

Post by cheybi »

I advise you to use GPR with 200Hz antenna, I used it many times for such project, it is good enough to detect your tunnel, the 400Hz antenna can't go that deep especially if soil is wet or contain clay.
Tomography is better for deeper and bigger target, also manipulating GPR is much easier... But you still need some help in that

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Re: Locating a man made tunnel

Post by Kknq »

geophix wrote:
Sat Mar 07, 2020 9:03 am
Kknq wrote:
Thu Mar 05, 2020 6:23 pm
Has anyone ever worked with RD1500? Would you rather choose the Easy Locator PRO HDR or RD1500? Thanks for any help in advance!
I would expect the penetration depths of RD1500 and Mala Easy Locator Pro HDR are very similar. The antenna frequency of RD1500 is 250MHz, lower than Mala's GPR; but Mala's GPR has the HDR technology (fast stacking as I mentioned before) to improve the signal/noise ratio, hence increase the penetration depth. I think the Mala WideRange HDR might be a better choice, it has better penetration depth (and resolution) and it's good for locating underground utilities if you want to keep it for your construction business. It has two antennas with 160 MHz and 670 MHz center frequencies, and it has the HDR technology, too.

Also, if you worry about data interpretation, you can post the data here and we might be able to help you to understand it.

Thanks for the indepth information! Sorry I have been quiet busy lately with the whole corona epidemy going on. Well, it looks like that we have decided to actually purchase the WideRange with the dual frequencies, even thought it will put me a bit more back I still think I got a good deal for 14'000 USD with the rough terrain cart, what do you think? It was a demo unit for a big company.

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Re: Locating a man made tunnel

Post by Kknq »

99thpercentile wrote:
Sat Mar 07, 2020 5:31 pm
Since it appears that you have more time than money, the target is relatively shallow, and relatively large versus the depth I would suggest electrical resistivity tomography. The DUOYI DY4300B 4-Terminal Earth Ground Resistance and Soil Resistivity Meter costs just over $300 USD for a kit with a resistivity meter, cables, and four electrodes. I would lay out a measuring tape perpendicular to the expected tunnel path and somewhere in the middle of search area. The electrode spacing will be 1 m, so put flags at each m mark along the tape. Since this will be an electrical resistivity tomography (ERT), which is a combination of a resistivity profile and a resistivity sounding, it will take a little while to collect each line. You will be using a dipole-dipole array for this particular data collection.

https://www.dyinstrument.com/duoyi/?q=e ... er/DY4300B

For the first profile you will use a 1 m “a” spacing. Put the electrodes at 0, 1, 2, and 3 m. Make a measurement and record the value. Then move the second two electrodes from 2 and 3 to 3 and 4 m, and make the next measurement. The first two electrodes are current electrodes (A & B), while the last two electrodes are the voltage potential electrodes (M & N). You will repeat this process until you get to the line.

All of your data will be entered into a spreadsheet for analysis. The tunnel may show up in just the pseudo section (plot of apparent resistivity versus approximate depth). If it doesn’t then the next step would be geophysical inversion. The standard software for this is RES2DINV, which is probably out of your budget, so you might have to use something free like boundless electrical resistivity tomography (BERT).

http://resistivity.net/bert/

I have only done this approach once to map out an escape tunnel from the world’s largest prison in Iraq. It was painfully slow, but it worked. The only reason I did it was that a former colleague insisted that I didn’t need the switching resistivity system, but once on site the base commander really wanted us to verify the tunnel location. It took three days to do a survey that would have taken a few hours with an automatic switching system.

Good luck, let me know if you have any questions.
Sorry for the late response, I am in the middle of my studies and balancing between two jobs so I dont have that much time coming back here. Well yes, it is true that I have more time on my hands than actually money :-) But Ill actually be able to purchase a used GPR after saving for over a year now.

I want to thank you for taking your time describing to me the process of the soil resitivity method. I ll keep this one in mind if we happen to be unlucky to find the tunnel with the GPR. But as mentioned before, I think with the measures of the tunnel, GPR should be able to quiet easily identify it.

Once again thanks for the info and Ill keep you all updated, as soon as Serbia takes away the travel ban Ill be able to travel back.

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Re: Locating a man made tunnel

Post by Kknq »

Hello everyone,

If you remember me I was actually able to conduct several survey on the said matter.
Ill attach you some images and I would be more then happy if someone could tell me, if this actually is what I am looking for!





Also I would be more than happy if someone could analize some of my data. I wanted to purchase GPR Slice, but due to financial problems I wont be able to purchase any soon. If someones able to analize my data, Id be more then happy to actually pay for it.

Thanks for reading

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Re: Locating a man made tunnel

Post by gmradar »

From the data above I’m not sure there is a tunnel anywhere.
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Re: Locating a man made tunnel

Post by geophix »

At least you can see some anomalies. If the anomalies were caused by a tunnel, the tunnel might have collapsed. I think the more important question is, how large the area have you scanned. If you see this kind of anomalies everywhere, it's probably not a tunnel. If it's the only anomaly area you see in a relatively large area, you might be on something.

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Re: Locating a man made tunnel

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geophix wrote:
Mon Sep 07, 2020 1:31 pm
At least you can see some anomalies. If the anomalies were caused by a tunnel, the tunnel might have collapsed. I think the more important question is, how large the area have you scanned. If you see this kind of anomalies everywhere, it's probably not a tunnel. If it's the only anomaly area you see in a relatively large area, you might be on something.
Hey! Thanks for your respond. Yes I have surveyed a very large area and this was the only area I got these anomlies. Could the anomlies be caused by anything else, have you ever seen a similare transect? Side note would be that the area is in the middle of nowhere and we know that for the last 300 years atleast, nothing was build upon this area.

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Re: Locating a man made tunnel

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gmradar wrote:
Mon Sep 07, 2020 12:37 pm
From the data above I’m not sure there is a tunnel anywhere.
What could cause such anomalies? I have surveyed the wholel area and this was the only area that showed anomalies. The contrast has been turned down all the way and it still shows a strong signal.

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Re: Locating a man made tunnel

Post by geophix »

To be honest, the anomalies do look like voids. I just realize that your tunnel might not be in a regular shape. I mean the top and walls of the tunnel might not be smooth at all. The GPR signals will bounce around inside the tunnel and show the signatures like the anomalies shown in your GPR profiles, especially the second one - which looks like it's crossing the tunnel.

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Re: Locating a man made tunnel

Post by gmradar »

Kknq wrote:
Tue Sep 08, 2020 3:32 am
gmradar wrote:
Mon Sep 07, 2020 12:37 pm
From the data above I’m not sure there is a tunnel anywhere.
What could cause such anomalies? I have surveyed the wholel area and this was the only area that showed anomalies. The contrast has been turned down all the way and it still shows a strong signal.
The only data that could be a void is the second one. The others look to me like a strong reflector from the ground, high contrast in dielectric between layers.
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Re: Locating a man made tunnel

Post by geophix »

Kknq, please see a void model and its gpr data simulation below. You can see there are apparent different responses between the two sides and the middle of the void. When the void spacing (depth wise) is small, you can easily get the "ringing" effect as shown at the two sides due waves bouncing between top and bottom of the void. There are much less ringing effect in the middle where the void is big. It's a similar situation where you have narrow underground passes. When you collect data across the underground pass (i.e. tunnel), the wave can easily bounce between two sides, showing the ringing effect. However, if you happen to collect the GPR data along the underground pass or over a large underground chamber, you will get less or no ringing effect. So I think your second GPR profile might be across the tunnel, and your first and 3r GPR profiles might be along the tunnel or over an underground chamber. But keep in mind that GPR or other geophysical data interpretation is an educated guess. You'll never know for sure what's underground until you dig to find out.
GPR data simulation model.jpg
simulated GPR data.jpg

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