geophone in borehole?

[John Beale]

Just thinking, as that's much easier than doing... Right now with the sensor on the concrete slab floor of my garage, I get a good bit of noise from the street out front (60 feet away) and the next street over which is 200 feet away.  I don't imagine it would be easy to do, but let's just say I was willing to consider drilling a geophone-diameter hole in the backyard to locate the sensor underground.  I believe the water table in my location is 40 feet down so I wouldn't go that far. Let's say I could somehow drill a 20 foot deep hole.  Would I see significantly less street noise at that depth? If the noise level is strictly proportional to distance, I would guess not, as the distance down is much less than the horizontal distance to the source.  I believe the soil in this area is just sandy clay (USGS map says "Alluvium"), no bedrock to be found.

[Eigil Haugen]

I believe this is a good idea and I think you would see less noise at 20 feet depth, because the traffic noise is surface waves. The amplitude of the surface waves are inverse proportional to distance. Body waves however are inverse proportional to distance-squared, so the surface waves travels much longer than the body waves underground. The surface waves also decay in depth quite fast. So putting the geophone "below" the surface waves should work. Although how deep waves decays in depth depends on the stiffness of the ground where you live and will also vary with frequency. I guess alluvium soil is relatively soft so perhaps it wont be too bad. You can look up Rayleigh waves if you want to investigate more about this.

 I have been thinking on doing something similar when my shake arrives and if background noise is too high. I live on soft clay with some traffic nearby. But the borehole seems difficult to make to me. I guess the hole would need some sort of casing to not cave in and I think I the water table is high.

[John Beale]

Ok, if I can avoid the surface waves, it might be worth while. I would also need to decide how to waterproof the sensor. I probably need some kind of casing, but then wouldn't the rigid casing pipe just conduct the surface noise that I don't want directly down to the sensor?  Or just backfill the hole again and abandon all hope of ever retrieving the sensor if it fails due to water ingress, etc.

Making a 2" diameter hole in clay soil seems possible: 

from http://www.drillyourownwell.com/

The DIY technique involves water pumped down the center of a PVC schedule 40 pipe used as both a drill stem and a drill bit.  At the bottom end of the PVC pipe a "drill bit" is fashioned by cutting teeth into the end of the PVC pipe.  The pipe is rotated back and forth as the PVC pipe is slowly worked into the ground while the cuttings are brought to the surface by the upward flow of water in the annular space around the pipe.

[chris...@aol.com]

Hi Eigil, 

    Download http://psn.quake.net/info/analysis.pdf

    At low frequencies, Surface Waves decrease in amplitude with the SQUARE of the distance 

between the source and the observer - assuming straight line transmission. The higher the frequency, 

the more the sound energy is absorbed. The amplitude decreases roughly exponentially with depth.  

    At low frequencies, the P and S Body Waves decrease in amplitude with the CUBE of the distance 

between the source and the observer - assuming straight line transmission. Again, the higher the 

frequency, the more the sound energy is absorbed along it's path. 

    Mounting a seismometer ~6 ft down will decrease the surface noise. Borehole seismometers may 

be 90 ft underground.                    

    

    Regards, 

    Chris

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[Eigil Haugen]

Hi Chris,

This confuses me. What I wrote I got from this text http://rses.anu.edu.au/~nick/teachdoc/lecture5.pdf
It say energy disperses as 1/r for surface waves and 1/r^2 for body waves. This is purely geometrical dispersion though. No material damping. Then I also read displacement decay proportional to  1/r^0,5 for surface waves from point loads at the surface. (https://pdfs.semanticscholar.org/8191/3736778978605b856225faf76f549f4cd1f1.pdf) Interior body waves in this case proportional to 1/r^2 and body waves along the surface as 1/r. And for line loads (like a train) there is no geometrical dispersion at all for Rayleigh waves.

Is the difference between what I wrote and what you wrote the material damping?

[John Beale]

Thanks for the comments. I don't know seismology, but I'm very confident the perimeter of a circle is proportional to r, and the surface area of a sphere (or half-sphere) is proportional to r^2, so signal energy vs. distance would be 1/r in 2D and 1/r^2 in 3D if it was just geometry. I assume any other power relationship has to be factoring in material-dependent properties like absorption, scattering and/or dispersion, that's what I'm not familiar with.

[chris...@aol.com]

Hi John, Fairbanks_Shake,

   Try using a small glass jar with a 'screw on' metal lid. Mount a suitable waterproof (Amphenol) cable 

gland in the center of the lid. Use a q-max hole cutter. Use audio coaxial cable with a woven Copper 

screen layer - this is far better than Cat5 cable. Push the cable through the gland and solder it to the 

geophone. Put it inside the jar and fill the jar with molten candle wax. After it has solidified, screw the 

lid on, tighten the gland to seal the cable entry and cover the lid with PVC tape.  

    Alternatively, seal the geophone + cable in the end of a long piece of PVC pipe and dig a suitable 

hole. You can buy post hole diggers - a ~4 ft T rod with a digging disk on the bottom end. Dig out 6" 

and pull the soil out. Dig another 6", etc. 

    You can also buy soil augers which are a tube with a bottom cutting edge mounted on a rod, or 

rods, attached to a T handle. The one that I used was about 2" OD and you could dig down to about 

12 ft. Check http://www.vanwalt.com/pdf/general/Hand-Augers-van-walt.pdf  and similar manufacturers. 

Also check Post Hole Borer - beg, borrow or hire one ? You can get motorized petrol augers which 

should be OK for making holes in frozen ground. 

    Regards 

    Chris
From: John Beale <beale...@gmail.com>
To: RaspberryShake <raspber...@googlegroups.com>
Sent: Tue, Dec 13, 2016 9:10 pm

Subject: [Raspberry Shake Community Forum] Re: geophone in borehole?

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[Ron H]

In my basement on the tile I am getting good signal with nice earthquakes in the 2.5 to 3.0 range however to minimize the noise from the basement floor I would like to place the geophone down a bore hole about 2 meters.

I started testing putting the geophone in a 1" PVC pipe sealing and burying it 1 meter down, but was not picking up any signal.  I put the geophone back on the floor with 1 meter wire leads to the shake board and still had no signal.  Then I cut the wire leads back to 6 inches and started getting signal again.  I was originally planning to bury the geophone 2 meter down and have 2 meters of wire back to the surface to the shake board above ground.  However when I increase the length of wires connecting the geophone to the shake board I am losing signal.

Below is a Swarm Image of the geophone placed on the basement floor in the same place.  The upper part 12/19 09:00- 20:00 is with 1 meter wire leads connecting geophone to shakeboard,   The bottom part 12/19 21:00 - 08:00 is with 6 inch wire leads connecting geophone to shakeboard. You can see in the image below that with the short leads I am getting great signal with three earthquake displayed, but the upper part I an just getting noise.   Do the length of the leads make that big of difference in the signal?  Is the wire picking up EMT noise?   Has anyone else used longer leads than the manual shows?  Would using the shielded coaxial cable be better that standard gage wire for the geophone leads? 

I would like to just bury the geophone and have long leads to the surface shakeboard Pi .  Or do I have to bury both the geophone and Pi with short leads?

Ron 

[Branden Christensen]

Hi Ron:

Is this a geophone we shipped or one you bought apart?

Branden

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[Ron H]

I have a  few strings of 30Hz and 10Hz geophones that we used for oil & gas seismic acquisition.

This is one of my 10hz geophones.

[chris...@aol.com]

Hi Ron, 

    You need a 4.5 Hz geophone. The RP has a x10 period extension circuit, which is probably 

oscillating with the longer leads. The geophone resistance needs to be 395 Ohm - what is the 

resistance of your geophone ? If it is less than this, try adding a resistor to make up the difference.

    Regards, 

    Chris

From: Ron H <rb.ha...@gmail.com>
To: RaspberryShake <raspber...@googlegroups.com>
CC: branden.christensen <branden.c...@osop.com.pa>
Sent: Wed, 21 Dec 2016 18:55
Subject: Re: [Raspberry Shake Community Forum] Re: geophone in borehole?

I have a  few strings of 30 Hz and 10 Hz geophones that we used for oil & gas seismic acquisition.
This is one of my 10 Hz geophones.

[Branden Christensen]

Thanks Chris.

Ron, I encourage you to keep playing with your setup to make things work but I cannot guarantee anything for your special setup. Our analog front end was tailored tightly to our Racotech 4.5 Hz 395 Ohm geophones. And we only tested these with the short twisted pairs you see in the youtube videos.

Best, Branden

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[John Stuart]

I achieved a significant reduction in noise level when I moved my RShake to a small 2'x2' concrete pad not in contact with my house, driveway, or street foundations & curbs (see "building a Seismic Vault" thread.)

I would still like to reduce the street traffic vibrations, so a borehole might work.  I do have an old soil bore analysis, so I expect the 'bedrock' sandstone is about 10 to 12 ft deep.  But first, I'd like to experiment with going down just a few feet.  Here's an idea I had for something simple.

The RShake's geophone can slip right down inside a 1" Sch.40 PVC pipe.  A 3/4" PVC slip plug is a press-fit inside the 1" pipe, but if you heat the pipe in boiling water, it will slip in and make a dandy end cap with flush sides.  

      

So by moving the geophone a few feet underground, I would hope to eliminate the thermal expansion popping I am recording from the plastic case exposed to the ambient temperature swings, and maybe some of the vehicle traffic noise.

But how to drill a hole?

If I can water-jet and pound a hole deep enough with a round wooded tree stake (and then pull it out), the above capped 1" PVC would fit down the hole.  Or I could drill a deeper and larger hole, to fit a 1-1/4" PVC pipe with end-cap, then cement it in place like a well casing for the 1"PVC geophone pipe. There's also YouTube's numerous water well drilling videos. But,,, will the seismic coupling between the soil and a small 1" pipe be as good as between the soil and a 2' x 2' concrete slab??  If I get down to the sandstone rock, will the street traffic become stronger?  

John Stuart (RFD2F)

Lafayette, CA

  .

[Angel Rodriguez]

Hi John,

Merry Christmas!

There are lots of youtube video on how to drill a hole by hand.  Try something like "drilling for water by hand"  I have a small borehole that goes down about 10 meters.  I have been giving this some thought.  I think that I am gong to gimble mine.  Who know when I will have time.

Keep us informed

Regards,

Angel

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[chris...@aol.com]

Hi John, Fairbanks_Shake, 

   Try using a small glass jar with a 'screw on' metal lid to house a geophone. Mount a suitable waterproof (Amphenol) cable gland in the center of the lid. Use a q-max hole cutter. Use audio coaxial cable with a woven Copper screen layer - this is far better than Cat5 cable. Push the cable through the gland and solder it to the geophone. Put it inside the jar and fill the jar with molten candle wax. After it has solidified, screw the lid on, tighten the gland to seal the cable entry and cover the lid with PVC tape.  

    Alternatively, seal the geophone + cable in the end of a long piece of PVC pipe and dig a suitable 

hole. You can buy post hole diggers - a ~4 ft T rod with a digging disk on the bottom end. Dig out 6" 

and pull the soil out. Dig another 6", etc. 

    You can also buy soil augers which are a tube with a bottom cutting edge mounted on a rod, or 

rods, attached to a T handle. The one that I used was about 2" OD and you could dig down to about 

12 ft. Check http://www.vanwalt.com/pdf/general/Hand-Augers-van-walt.pdf  and similar manufacturers. 

Also check Post Hole Borer - beg, borrow or hire one ? You can get motorized petrol augers which 

should be OK for making holes even in frozen ground. 

    However, before doing ANYTHING like this, CHECK that the geophone is electronically stable and operates OK with that length of extension cable ! ! ! The input circuit to the RS has a negative impedance and it may be prone to oscillations with added cable capacitance.

    If the ground is dry, you can backfill the ring between the tube and the soil with dry sand, otherwise wash wet sand down the gap with a watering can / hose pipe / etc. This can take several attempts.  Remember that a tube which has been in the ground for some time may be very difficult to remove ! In time, the soil slowly compacts around the tube and grips it ~ proportional to the mass of the soil between the sensor and the surface of the ground ! 

   To get rid of surface noise seismologists drill down 100 ft or more. It is an advantage to use a mounting ~6ft below ground level - but you need to seal the hole at several levels to prevent convection.

    Regards 

    Chris
From: John Beale <beale...@gmail.com>
To: RaspberryShake <raspber...@googlegroups.com>
Sent: Tue, Dec 13, 2016 9:10 pm
Subject: [Raspberry Shake Community Forum] Re: geophone in borehole?

Ok, if I can avoid the surface waves, it might be worth while. I would also need to decide how to waterproof the sensor. I probably need some kind of casing, but then wouldn't the rigid casing pipe just conduct the surface noise that I don't want directly down to the sensor?  Or just backfill the hole again and abandon all hope of ever retrieving the sensor if it fails due to water ingress, etc.

Making a 2" diameter hole in clay soil seems possible: 

from http://www.drillyourownwell.com/

The DIY technique involves water pumped down the center of a PVC schedule 40 pipe used as both a drill stem and a drill bit.  At the bottom end of the PVC pipe a "drill bit" is fashioned by cutting teeth into the end of the PVC pipe.  The pipe is rotated back and forth as the PVC pipe is slowly worked into the ground while the cuttings are brought to the surface by the upward flow of water in the annular space around the pipe.

On Tuesday, December 13, 2016 at 12:08:52 PM UTC-8, Eigil Haugen wrote:

I believe this is a good idea and I think you would see less noise at 20 feet depth, because the traffic noise is surface waves. The amplitude of the surface waves are inverse proportional to distance. Body waves however are inverse proportional to distance-squared, so the surface waves travels much longer than the body waves underground. The surface waves also decay in depth quite fast. So putting the geophone "below" the surface waves should work. Although how deep waves decays in depth depends on the stiffness of the ground where you live and will also vary with frequency. I guess alluvium soil is relatively soft so perhaps it wont be too bad. You can look up Rayleigh waves if you want to investigate more about this. 

 I have been thinking on doing something similar when my shake arrives and if background noise is too high. I live on soft clay with some traffic nearby. But the borehole seems difficult to make to me. I guess the hole would need some sort of casing to not cave in and I think I the water table is high. 



tirsdag 13. desember 2016 01.56.09 UTC+1 skrev John Beale følgende:

Just thinking, as that's much easier than doing... Right now with the sensor on the concrete slab floor of my garage, I get a good bit of noise from the street out front (60 feet away) and the next street over which is 200 feet away.  I don't imagine it would be easy to do, but let's just say I was willing to consider drilling a geophone-diameter hole in the backyard to locate the sensor underground.  I believe the water table in my location is 40 feet down so I wouldn't go that far. Let's say I could somehow drill a 20 foot deep hole.  Would I see significantly less street noise at that depth? If the noise level is strictly proportional to distance, I would guess not, as the distance down is much less than the horizontal distance to the source.  I believe the soil in this area is just sandy clay (USGS map says "Alluvium"), no bedrock to be found.

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From: John Stuart <qxst...@gmail.com>
To: RaspberryShake <raspber...@googlegroups.com>
Sent: Sat, Dec 24, 2016 11:32 pm
Subject: [Raspberry Shake Community Forum] Re: geophone in borehole?

I achieved a significant reduction in noise level when I moved my RShake to a small 2'x2' concrete pad not in contact with my house, driveway, or street foundations & curbs (see "building a Seismic Vault" thread.)

I would still like to reduce the street traffic vibrations, so a borehole might work.  I do have an old soil bore analysis, so I expect the 'bedrock' sandstone is about 10 to 12 ft deep.  But first, I'd like to experiment with going down just a few feet.  Here's an idea I had for something simple.

The RShake's geophone can slip right down inside a 1" Sch.40 PVC pipe.  A 3/4" PVC slip plug is a press-fit inside the 1" pipe, but if you heat the pipe in boiling water, it will slip in and make a dandy end cap with flush sides.  

      

So by moving the geophone a few feet underground, I would hope to eliminate the thermal expansion popping I am recording from the plastic case exposed to the ambient temperature swings, and maybe some of the vehicle traffic noise.

But how to drill a hole?

If I can water-jet and pound a hole deep enough with a round wooded tree stake (and then pull it out), the above capped 1" PVC would fit down the hole.  Or I could drill a deeper and larger hole, to fit a 1-1/4" PVC pipe with end-cap, then cement it in place like a well casing for the 1"PVC geophone pipe. There's also YouTube's numerous water well drilling videos. But,,, will the seismic coupling between the soil and a small 1" pipe be as good as between the soil and a 2' x 2' concrete slab??  If I get down to the sandstone rock, will the street traffic become stronger?  

John Stuart (RFD2F)

Lafayette, CA

  .

On Monday, December 12, 2016 at 4:56:09 PM UTC-8, John Beale wrote:

Just thinking, as that's much easier than doing... Right now with the sensor on the concrete slab floor of my garage, I get a good bit of noise from the street out front (60 feet away) and the next street over which is 200 feet away.  I don't imagine it would be easy to do, but let's just say I was willing to consider drilling a geophone-diameter hole in the backyard to locate the sensor underground.  I believe the water table in my location is 40 feet down so I wouldn't go that far. Let's say I could somehow drill a 20 foot deep hole.  Would I see significantly less street noise at that depth? If the noise level is strictly proportional to distance, I would guess not, as the distance down is much less than the horizontal distance to the source.  I believe the soil in this area is just sandy clay (USGS map says "Alluvium"), no bedrock to be found.

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[Eigil Haugen]

This is a very interesting discussion and I might try something similar when my Shake arrives (currently in Norwegian customs for toll declarations).

At my place there is about half meter of gravel/sand fill and lots of soft marine clay underneath. I was thinking to use 10-15 cm diameter casing for the gravel part and then 5 cm for the entire length after that. Hopefully this prevents the tubes from transmitting noise. Then finally some sort of container with the geophone placed at the bottom.

Do you have any hints on how to ensure that the geophone is installed no inclination? How does one test it? The hole may be a bit off and placing the geophone container exactly right could be tricky too. I can probably borrow hand augers, rods and a rod jack for making this hole.

[John Stuart]

I bored a 4 ft. deep test hole today using a homemade 1.6" diameter PVC drilling tool.  Tomorrow I'll lower the RShake sensor down the 1" PVC sensor tube and see if my street traffic is attenuated.

      

     

That's my Son who stopped by at just the right time to play with Pops.  PVC 'drill bit' did cut through some 1/4" roots, but making a metal version would have been much better.

After boring the hole, I inserted a  5 ft. long, 1" PVC sensor tube down the hole, then back-filled with sand. See my earlier post for photos of sensor tube.

 Tomorrow I'll use some  Belden 9841 #24 shielded pair cable to lower the geophone down this 1" PVC pipe and connect to the RShake board.

That's my home in the background, 100' away, and my street is 100' further away.

I found lots of good hole drilling ideas on this website: http://www.drillyourownwell.com/index.htm 

John Stuart

Lafayette CA

[Eigil Haugen]

That looks great! I look forward to hear about how it supresses the surface noise. What sort of soils did you encounter from the boring? One could probably try to estimate vertical decay of Rayleigh waves but that depends on wavelength (soil propagation velocity).

By the way, I am home from holidays now and can finally pick my Shake from the post office. Hopefully it is up and running next week.

Best regards
Eigil

[John Stuart]

Yesterday I moved my backyard RShake (RFD2F) to a location 75 feet from my house, and lowered the sensor down a 1" PVC pipe, 4 feet down.

The sensor pipe was inserted into a hole drilled into sandy clay (no bedrock) then back-filled with sand displacing the water left in the hole from drilling.

I have a 2nd RShake (RFE6E) sitting on my concrete basement floor.

Attached is a Swarm image showing both RShakes, side-by-side, for easy comparison. 

Observations:

1. In the middle of the night, both locations had almost identical RMS count levels. At my location, at night, the RMS amplitude is dependent on Pacific Ocean wave heights as they approach the San Francisco Coast. 
   http://www.ndbc.noaa.gov/show_plot.php?station=46026&meas=sght&uom=E&time_diff=-8&time_label=PST  
   
   
2. Street traffic is only slightly attenuated (10 - 20%) for the buried sensor, probably due to being further away from the street (200 ft. vs. 100 ft.)
3. House 'cultural'  noise is almost totally attenuated to below the background noise. Distance from house probably more important than being buried 4 ft.
   
4. Eliminated thermal 'pops' I was seeing when backyard RShake was outdoors in the orange drybox.  I think these occasional, single shot, bi-directional, "pops' were due to the acrylic strap that holds the geophone in place, when the ambient temperature changes causes the acrylic to expand and contract.
5. Deer footsteps easy to identify, as they take a few steps, stop and look around, then take some more steps.  I think the two I saw yesterday were out celebrating New Year's at 3:30 AM local.
6. Still waiting for a verifiable earthquake to compare sensitivity. 

Conclusions:

1. Moving further from house probably did more good than burying the sensor.
   
2. Burying may have eliminate air-bore nose from neighbor's pool pumps and HVAC.
3. Street traffic vibration is conducted through the earth, so burying sensor had little effect. (However, I had previously found street traffic was being conducted down my concrete driveway to my house foundation / basement.)

John Stuart

Lafayette, CA
.  

[Angel Rodriguez]

Hi John,

Thanks for sharing.  

I find your traffic noise to be an important bit quiter, every little bit helps.  I just moved mine to a quieter place and I plan to put one a shallow hole sometime soon.  all I need is a bit of time.

Regards,

Angel

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[John Stuart]

Earthquakes Recorded by Buried Sensor

Attached are three examples of earthquakes recently recorded by the RShake geophone I installed 4 ft. underground, down a 1" PVC pipe. (see my earlier post in this thread.)

In two cases, the sensitivity was identical to another RShake sitting on my concrete basement floor, 100 ft. away.  In the third case (M1.2), the buried sensor was a little bit better (about 100 more counts) than the basement sensor.

A big surprise was how much better the RShake detected the M1.2 compared to a professional seismometer (4th attached file) over in Berkeley, 10km further from the quake.

FYI, I used the Berkeley "Make Your Own Seismogram" application  to make the last attachment:  http://quake.geo.berkeley.edu/bdsn/seismograms.html

John Stuart

Lafayette CA 

[Branden Christensen]

Why so surprised? RShake is the real deal ;)

Thanks John!

Branden

Director, OSOP

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[chris...@aol.com]

Hi John, 

      What was the distance between you and the epicenter of that M 1.2 quake, please ? The signals from local quakes fall off quite rapidly with distance, so a  further 10 Km range could be significant - you are talking about body waves, not surface waves.   

    Regards, 

    Chris

From: John Stuart <qxst...@gmail.com>
To: RaspberryShake <raspber...@googlegroups.com>
Sent: Mon, Jan 2, 2017 3:59 pm
Subject: [Raspberry Shake Community Forum] Re: geophone in borehole?

[John Stuart]

Chris,

The M1.2 was 17km from me, as I noted in red text below.

John Stuart

[F5HNK Patrick]

Hmm, John, you shouldn't blame the Berkeley seismic station, it is a Broadband sensor. Would you high-pass-filter out the signal from the BKS station, you would see the high frequency components of the local quake standing out of a flat waveform...

The Shake is a short period sensor, perfectly designed for local earthquakes. The expensive broadband station can also do this, and more...

Does it make sense ?

Patrick

PS: Branden should have mentionned that point  ;-)

[John Beale]

@John S: Very interesting to see this borehole experiment, thanks for doing it and posting about it!  Maybe 4' down isn't very far, but I still wonder about the PVC casing of your borehole. If there was a difference in vertically-oriented noise between surface and some depth, I wonder if the relatively rigid pipe would efficiently channel any surface noise down to the sensor, unless there is some gap between sensor and pipe filled with sand etc.

[John Stuart]

John B.

The 5ft. length of 1" PVC is empty, except for the sensor and cable. The sensor is sitting on the shoulder made by the 3/4" plug pushed up inside the 1" PVC.  I stuffed a little bit of extra Belden cable down the pipe to make sure the sensor stays in full contact with the bottom plug shoulder.  I didn't want to fill the pipe with sand for fear of not being able to pull the sensor out (when I drill a deeper borehole).

 So I consider the entire length of PVC pipe to be part of the vibration coupling path, be it seismic coming up from the ground, or raindrops hitting the top (until I put a little roof over it).  Also, the closed piece of PVC may have had a few sudden length changes yesterday as air pressure equalized, in and out, via the pipe threads containing rain water droplets, until I sealed the threads with PTFE thread sealant.

Surrounding the outside length of buried PVC pipe (about 4 ft.), there is about 1/2" of sand I poured in around the pipe, while wiggling the pipe and displacing the water still in the hole. So it has set-up fairly firm.  Next time I may mix in some cement, but I think the sand 'slurry' is drying out to be stiff enough not to attenuate 23 Hz vibrations, the sensor's max. range.  Attached is some proof of that, comparing 18 to 25 Hz vibrations coming from our bed.  (No, I'm not that young! Our bed frame has multiple variable speed motors. 

John S.

[John Beale]

All very interesting data. Looks like the sensor on the concrete is seeing more signal above 25 Hz being aliased down (folded over), but the relative levels below 25 Hz look quite similar between the two. Actually, it's impressive how that signal travels so well to the buried sensor 75' away.

On Wednesday, January 4, 2017 at 4:32:37 PM UTC-8, John Stuart wrote:

... Attached is some proof of that, comparing 18 to 25 Hz vibrations coming from our bed.  (No, I'm not that young! Our bed frame has multiple variable speed motors. 

[Skip]

Hmmm... this bad boy (see attached picture) that has graced our back yard for almost 100 years has about 140 feet of 6" diameter cased hole below it. The tubing, rod, and pump were removed last summer, and the casing seems sound. The surface equipment is just a lawn ornament now and covers the still-open hole. Water level is about 40' below the surface. 

I oughta be able to use that borehole for *something*.

Skip - AM.R3AA7

[Angel Rodriguez]

Hi Skip,

If I had a borehole like that I would 100% be trying to put a sensor down.  How high is the column of water in that well?

If you decide to do it let's talk!

Angel

Shake forum on google.groupsSome useful links:

 
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[Kelly Gann]

So, if you were to say.. fill the pipe up past the waterline with a grout solution or concrete, would placing the sensor on top of that emulate bedrock in stability and conduction? 

-Kelly

On Thursday, January 5, 2017 at 3:33:35 PM UTC-8, Angel Rodriguez wrote:

Hi Skip,

If I had a borehole like that I would 100% be trying to put a sensor down.  How high is the column of water in that well?

If you decide to do it let's talk!

Angel

Shake forum on google.groupsSome useful links:

 
Manual: http://manual.raspberryshake.org/
Shop: https://shop.raspberryshake.org/
Website: http://raspberryshake.org/
Do It YourSelf Page: http://raspberryshake.org/do-it-yourself

On Thu, Jan 5, 2017 at 5:15 PM, Skip <sandfwh...@gmail.com> wrote:

Hmmm... this bad boy (see attached picture) that has graced our back yard for almost 100 years has about 140 feet of 6" diameter cased hole below it. The tubing, rod, and pump were removed last summer, and the casing seems sound. The surface equipment is just a lawn ornament now and covers the still-open hole. Water level is about 40' below the surface. 

I oughta be able to use that borehole for *something*.

Skip - AM.R3AA7

On Monday, December 12, 2016 at 6:56:09 PM UTC-6, John Beale wrote:

Just thinking, as that's much easier than doing... Right now with the sensor on the concrete slab floor of my garage, I get a good bit of noise from the street out front (60 feet away) and the next street over which is 200 feet away.  I don't imagine it would be easy to do, but let's just say I was willing to consider drilling a geophone-diameter hole in the backyard to locate the sensor underground.  I believe the water table in my location is 40 feet down so I wouldn't go that far. Let's say I could somehow drill a 20 foot deep hole.  Would I see significantly less street noise at that depth? If the noise level is strictly proportional to distance, I would guess not, as the distance down is much less than the horizontal distance to the source.  I believe the soil in this area is just sandy clay (USGS map says "Alluvium"), no bedrock to be found.

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[Angel Rodriguez]

I would put the Shake all the way down and then fill a bit with sand to couple the sensor to the pipe.  The reason I asked for the hight of the water column was to determine what pressures I would be dealing with when I made the water proof case,.

Angel

On Thu, Jan 5, 2017 at 7:11 PM, Kelly Gann <kelly....@gmail.com> wrote:

So, if you were to say.. fill the pipe up past the waterline with a grout solution or concrete, would placing the sensor on top of that emulate bedrock in stability and conduction? 

-Kelly

On Thursday, January 5, 2017 at 3:33:35 PM UTC-8, Angel Rodriguez wrote:

Hi Skip,

If I had a borehole like that I would 100% be trying to put a sensor down.  How high is the column of water in that well?

If you decide to do it let's talk!

Angel

On Thu, Jan 5, 2017 at 5:15 PM, Skip <sandfwh...@gmail.com> wrote:

Hmmm... this bad boy (see attached picture) that has graced our back yard for almost 100 years has about 140 feet of 6" diameter cased hole below it. The tubing, rod, and pump were removed last summer, and the casing seems sound. The surface equipment is just a lawn ornament now and covers the still-open hole. Water level is about 40' below the surface. 

I oughta be able to use that borehole for *something*.

Skip - AM.R3AA7

On Monday, December 12, 2016 at 6:56:09 PM UTC-6, John Beale wrote:

Just thinking, as that's much easier than doing... Right now with the sensor on the concrete slab floor of my garage, I get a good bit of noise from the street out front (60 feet away) and the next street over which is 200 feet away.  I don't imagine it would be easy to do, but let's just say I was willing to consider drilling a geophone-diameter hole in the backyard to locate the sensor underground.  I believe the water table in my location is 40 feet down so I wouldn't go that far. Let's say I could somehow drill a 20 foot deep hole.  Would I see significantly less street noise at that depth? If the noise level is strictly proportional to distance, I would guess not, as the distance down is much less than the horizontal distance to the source.  I believe the soil in this area is just sandy clay (USGS map says "Alluvium"), no bedrock to be found.

--

-- 

[John Stuart]

and Speaking of Water in a Bore Hole, , ,

my buried sensor started going nuts at 20:31:33 today  (see RFD2F).

As I suspected, enough water had seeped into the 1" PVC bore pipe to 'short' out the sensor's terminals. After removing the water the sensor is working fine now.

I found that my heat shrink tubing was not making a watertight seal against the Belden cable, and rain water had wicked right down into the bore pipe.

Since this first photo was taken, I have added a very classy rain shield, and added PFTE paste to the plastic pipe threads.

 

John Stuart

Lafayette, CA

[Skip]

We pulled about 138' of tubing and downhole equipment from the well. The water level was about 40' below the surface (estimated by timing the fall of small rocks) before we covered it with the equipment at the surface in early October, so, call it up to about 100' (30m). 

The bottom hole is probably silted up (the bottom-most tubing was discolored in a muddy shade), so it may not be possible to easily reach the TD of the well without cleaning it out. A weighted line would probably give a realistic answer to the effective depth of the hole and how deep the water is.

Skip - AM.R3AA7

On Thursday, January 5, 2017 at 5:33:35 PM UTC-6, Angel Rodriguez wrote:

Hi Skip,

If I had a borehole like that I would 100% be trying to put a sensor down.  How high is the column of water in that well?

If you decide to do it let's talk!

Angel

Shake forum on google.groupsSome useful links:

 
Manual: http://manual.raspberryshake.org/
Shop: https://shop.raspberryshake.org/
Website: http://raspberryshake.org/
Do It YourSelf Page: http://raspberryshake.org/do-it-yourself

On Thu, Jan 5, 2017 at 5:15 PM, Skip <sandfwh...@gmail.com> wrote:

Hmmm... this bad boy (see attached picture) that has graced our back yard for almost 100 years has about 140 feet of 6" diameter cased hole below it. The tubing, rod, and pump were removed last summer, and the casing seems sound. The surface equipment is just a lawn ornament now and covers the still-open hole. Water level is about 40' below the surface. 

I oughta be able to use that borehole for *something*.

Skip - AM.R3AA7

On Monday, December 12, 2016 at 6:56:09 PM UTC-6, John Beale wrote:

Just thinking, as that's much easier than doing... Right now with the sensor on the concrete slab floor of my garage, I get a good bit of noise from the street out front (60 feet away) and the next street over which is 200 feet away.  I don't imagine it would be easy to do, but let's just say I was willing to consider drilling a geophone-diameter hole in the backyard to locate the sensor underground.  I believe the water table in my location is 40 feet down so I wouldn't go that far. Let's say I could somehow drill a 20 foot deep hole.  Would I see significantly less street noise at that depth? If the noise level is strictly proportional to distance, I would guess not, as the distance down is much less than the horizontal distance to the source.  I believe the soil in this area is just sandy clay (USGS map says "Alluvium"), no bedrock to be found.

--
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Manual: http://manual.raspberryshake.org/
Shop: https://shop.raspberryshake.org/
Website: http://raspberryshake.org/
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[Kelly Gann]

Ahh, understood..  

[chris...@aol.com]

Hi John, 

    Suggestion !
    Solder the cable onto the geophene. Drop the geophone and cable into a suitable length of 1" PVC tube. Wedge the geophone in the bottom. Stick on a PVC end cap and give it a day to harden. Put chips of candle wax down the tube sufficient to easily cover the geophone and the end of the cable. Dip the tube in ~70 C water to liquefy the wax. Allow it to cool solid, locking the geophone in place and sealing the cable. Drill another end cap for a suitable Cambion cable gland and install the gland. Pass the cable through the gland and glue the cap to the tube. Tighten the gland to seal the cable into the tube. Feed the tube into a suitable hole in the ground. Add sand to fill the gap between the tube and the ground. Cover over the tube and connect the cable to the RShake electronics.

    Regards, 

    Chris

From: John Stuart <qxst...@gmail.com>
To: RaspberryShake <raspber...@googlegroups.com>
Sent: Fri, Jan 6, 2017 12:55 am
Subject: [Raspberry Shake Community Forum] Re: geophone in borehole?

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[Eddy]

Hello,

@John Stuart, any plans to deepen the existing borehole which is 4ft deep now? Just wondering whether going deeper would reduce further traffic noises and by how much. Maybe other things are keeping you busy too...

I plan to get a shake and it seems placing the geophone into a borehole is the better option to reduce cultural noises. Thinking of going about 10ft deep, and the data available for now from here is 4ft. Anyone else has done this and willing to share? 

Many thanks.

Eddy

On Sunday, December 25, 2016 at 7:32:54 AM UTC+8, John Stuart wrote:

I achieved a significant reduction in noise level when I moved my RShake to a small 2'x2' concrete pad not in contact with my house, driveway, or street foundations & curbs (see "building a Seismic Vault" thread.)

I would still like to reduce the street traffic vibrations, so a borehole might work.  I do have an old soil bore analysis, so I expect the 'bedrock' sandstone is about 10 to 12 ft deep.  But first, I'd like to experiment with going down just a few feet.  Here's an idea I had for something simple.

The RShake's geophone can slip right down inside a 1" Sch.40 PVC pipe.  A 3/4" PVC slip plug is a press-fit inside the 1" pipe, but if you heat the pipe in boiling water, it will slip in and make a dandy end cap with flush sides.  

[dave d]

I'm going to play around with some options. The 1 inch PVC vs 4 inch PVC casing with 1 inch PVC centered in the annulas. Watched a video clip on reducing pile driving noise transmission 90 percent by isolating pile in an outer casing with air gap.

[paul denton]

David

did you ever go ahead  and try this borehole installation  ?

cheers paul denton (pde...@bgs.ac.uk) 

[Jim Skinner K6BPT]

You might just want to build a simple seismic instrument pier.  My geophone pier is a round cardboard tube inside of a hole dug into my yard that is filled with 275 pounds of concrete.

The bottom 2 feet of this pier is in direct contact with the ground and the top foot is surrounded with fine grained sand.  The "sides of the "hole" are approx 4 to 6 inches away from

the pier.  Mount your seismic gear (shake or geophones) on top using a single anchor.  This instrument pier is only 75 feet from the street and does a good job of isolation local traffic.

If you are a glutton for punishment you can go with a larger instrument pier such as the 9600 Lb + shown that is inside of my "seismo vault".

Jim Skinner, K6BPT  

[Ben7230, (R9F34)]

Hi Jim,

Could you provide some more details on the cardboard tube pier. How deep does it go and does the depth help with isolating local traffic or does more weight help? I have my Raspberry Shake around 200 meters away from the road and I can still see a motorbike on the road from a 300 to 400 meter away. Granted, it is a gravel or stone road. I think that they used 3'' material, so It is rough and will show up more. I live in Costa Rica and that is how the rural roads are here. What does the sand do? Is it necessary? I would have to have mine above ground because in the rainy season our ground gets saturated with water and even a very shallow hole will fill with water. I thought about doing a bore hole but this looks simpler.

Benjamin

[John Beale]

I am curious about the seismic sensor difference between a small pier 3' deep, and the concrete slab of a garage which is 6" deep, at roughly the same distance from the road. I would not have expected a huge difference with the added 2.5 feet of depth but maybe there is? I'm sure there would be more attenuation at the higher frequencies as you go further below the surface, but don't have a feeling for how much.  I assume the sand around the top is to avoid strongly coupling the topmost (most noisy) ground surface directly to the pier.

[Jim Skinner K6BPT]

- Benjamin -

The cardboard tube is around three feet long and centered on a "pool" of poured concrete that is about 2 feet below the top of the sand layer so that there is about 1 foot of concrete pier above

the top of the sand.  You can move the whole thing up so that the top of the pier is above local ground level and cover it with a sprinkler housing that pokes above ground level.  The important

thing is to make sure there is loose medium/fine sand between the pier and the hole in the ground as the layer of sand attenuates local vibrations.  More weight does help and the deeper that you can make it (within reason of course), the better.  The ground that mine is installed in is Sun baked hard pan and we needed to use a jack hammer to dig the hole.  Then I lined the hole with concrete bricks and poured in the sand.  I suspect that in your area, you will have many feet of topsoil that will be pretty easy to dig in.  Of course, if you can get to bedrock, so much the better !

Jim, K6BPT 

[Jim Skinner K6BPT]

- John -

The biggest difference is the torquing moment that the garage will impart to the slab, even with good footers around the perimeter of the garage.  A separate pier, relatively low to the ground doesn't have the wind modulation that a building does.  Exactly the reason for the top level of sand, it affords a very loose coupling to the ground around it.  My "main" instrument pier has a 2 inch buffer of sheet Styrofoam all the way around the 9600 Lb pier from top to bottom and is only "coupled" to the ground at the very bottom of the pier.

Jim, K6BPT 

[Ben7230, (R9F34)]

-Jim-

Thanks for the explanation. 

Bedrock! I don't even know how deep I would need to go. I have a 55 meter well and we hit sand! The ground here is very little top soil maybe about 6 inches then it is red/orange dirt which is fairly hard. We need to use a pick to dig a hole. 

I will have to see what I can do.

Thanks Benjamin

[James Skinner]

- Benjamin -

That's the sort of dirt that I had to dig thru for my geophone pit as well as the main instrument pier where the hole was dug to 48" x 48" x 72" and took three months to dig out.  Not a project for the faint of heart or anyone older than 40.  We didn't have the advantage of 6 inches of top soil though.  This stuff is even hard to drive a 40d nail into with a hammer. 

Jim, K6BPT

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[Kristi Fink]

My raspberry Shake has been working just fine inside of our house which is on a 6-foot slab of concrete for a foundation. It's not ideal 4 it to be inside the house, on the wood floor, tucked away in a corner. I have two small children and they are very boisterous active loud and everywhere in the house. However, I have found that I can usually filter out their noise pretty easily. My other seismograph, which is an eq1 vertical seismometer, is out in a somewhat quieter place in the garage sitting on the concrete slab itself. It to receives a lot of background noise. I think that's simply due too as we live immediately adjacent to the ExxonMobil campus and there is, as you can imagine, a ton of traffic. You can actually see every time I open my garage door on the seismograph because it creates a huge Peak. Let me log on to my computer and I will show you the steps on how to enable other features on the Helocorder

Kristi Fink
817-300-2695

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