PSN-L Email List Message

Subject: Re: crawl space under house
From: tchannel1@............
Date: Sat, 30 Aug 2008 15:39:05 -0600


Re: crawl space under houseHi Bob,  Thanks for =
sharing...........Presently my sensors are in the basement on a concrete =
floor.   Yes I do see people walking upstairs, but mostly if I place the =
sensor close to a vertical wall.
My new house set on a new foundation, so as you point out I may get a =
lot of noise as the house settles.   We shall see.   All your =
information is good to know.

Ted
  ----- Original Message -----=20
  From: Bob Hancock=20
  To: psn-l@.................
  Sent: Saturday, August 30, 2008 12:40 PM
  Subject: Re: crawl space under house


  Hi Ted -

  When we lived in NJ, I operated a 3 channel MET seismometer in the =
crawl space under my apartment.   I had the instrument sitting on a =
hexagonal cement block of 12 inches across and 2 inches thick, all =
covered with a Styrofoam bucket.  The building design included =
foundation walls that were placed several feet in the soil, including =
individual foundations walls between each apartment.  Although I had the =
instrument more or less in the middle of the area, I found that as I =
walked on the floor above, I could see that motion on the instrument.  =
Depending upon your foundation, you may find that walking around your =
house will cause deflections of the instruments.  I have heard similar =
comments from individuals who have placed instruments in basements or on =
garage floors.

  When we moved to Arizona, I tried a variety of locations including =
under my house, in a nearby storage shed and in my workshop.  None were =
adequate.  I finally placed the instrument in the ground, first about 75 =
feet away and I could always tell when the washing machine when into the =
spin cycle.  I finally moved the instrument about 250 feet from the =
house where I get a minimum of wind and cultural noise.  The road is =
about 400 feet from the instrument and I can see vehicles striking =
potholes in the road.  I find that if I drive my garden tractor within =
50 feet of my vault, I can see movement on the instrument. =20

  Depending upon your yard size, you might consider a subsurface vault =
in a quiet area, away from trees and any buildings.  It is very =
difficult to remove cultural noise as I have found.  However, you should =
be careful and do not disturb any more dirt than you need.  Dirt once =
disturbed is difficult to re-compact and will be a source of noise for a =
long time to come as it settles.  I have found that after 1 1/2 years, I =
still get occasional ground noise from settling dirt.

  Another thought to consider is insulating your instrument from wind =
currents.  Seismometers are extremely sensitive to any wind flow and =
temperature change.  In my setup, I first covered my instrument with =
sand bags, and that did a good job of insulating the instrument from =
thermal variation and wind flow.  However, they were hard to remove from =
the hole, and I settled on a large bucket lined with fiberglass which =
sits on top of the instrument and covers it down to its base.  I have =
found this to be very effective and the bucket protects the instrument =
from both wind flow and thermal variations.  Even in a sealed seismic =
vault you need to protect against errant wind currents caused by uneven =
thermal heating of the vault as the sun moves across the sky.

  The key for a quiet instrument is reduction of cultural noise and wind =
noise.  Things to consider is under a house you will most likely pick up =
movement of people in the house, and tilt from the house in times of =
high and possibly even moderate winds.  You proximity to trees is =
another consideration as the root structure causes ground tilt for a =
considerable distance.  Railroad tracks can transmit vibrations for =
miles.  The worst rail noise comes from diamonds where one set tracks =
crosses another set of tracks.  Major roads that are in poor repair with =
potholes and lots of semi-trailers are another source of cultural =
noise.......Just some thoughts to consider.

  Good luck on your location wherever you choose it.

  Bob Hancock




      ----- Original Message -----=20
      =20
      From:  Gary  Lindgren  =20
      =20
      To: psn-l@.................
      =20
      Sent: Thursday, August 28, 2008 9:59  AM
      =20
      Subject: craw space under house

      Hi All,    I am building a new house.   This house has no =
basement, but has a  24"? crawlspace under the house.   I have lots of =
time, to create a  space for my three sensors, under the house.   I =
could also place  them in the garage on the concrete floor.   My thought =
was to enter  the crawlspace, and dig a small pit large enough to allow =
for elbow room, then  line the pit with concrete blocks to keep dirt =
away.  Perhaps  covering the floor area similarly.  Concrete may not be =
the best  material.   I could also pour a pad or small footing using  =
cement.

      =20

      Please any thoughts  on preparing this space?

      =20

      =20
      =20
      =20

      Thanks,  Ted





Re: crawl space under house





Hi Bob,  Thanks for=20 sharing...........Presently my sensors are in the basement on a concrete = floor.   Yes I do see people walking upstairs, but mostly if I = place=20 the sensor close to a vertical wall.
My new house set on a new foundation, = so as you=20 point out I may get a lot of noise as the house settles.   We = shall=20 see.   All your information is good to know.
 
Ted
----- Original Message -----
From:=20 Bob=20 Hancock
To: psn-l@..............
Sent: Saturday, August 30, 2008 = 12:40=20 PM
Subject: Re: crawl space under=20 house

Hi Ted -

When we lived in NJ, I = operated a 3=20 channel MET seismometer in the crawl space under my apartment. =   I=20 had the instrument sitting on a hexagonal cement block of 12 inches = across and=20 2 inches thick, all covered with a Styrofoam bucket.  The = building design=20 included foundation walls that were placed several feet in the soil, = including=20 individual foundations walls between each apartment.  Although I = had the=20 instrument more or less in the middle of the area, I found that as I = walked on=20 the floor above, I could see that motion on the instrument. =  Depending=20 upon your foundation, you may find that walking around your house will = cause=20 deflections of the instruments.  I have heard similar comments = from=20 individuals who have placed instruments in basements or on garage=20 floors.

When we moved to Arizona, I tried a variety of = locations=20 including under my house, in a nearby storage shed and in my workshop. =  None were adequate.  I finally placed the instrument in the = ground,=20 first about 75 feet away and I could always tell when the washing = machine when=20 into the spin cycle.  I finally moved the instrument about 250 = feet from=20 the house where I get a minimum of wind and cultural noise.  The = road is=20 about 400 feet from the instrument and I can see vehicles striking = potholes in=20 the road.  I find that if I drive my garden tractor within 50 = feet of my=20 vault, I can see movement on the instrument.  

Depending = upon your=20 yard size, you might consider a subsurface vault in a quiet area, away = from=20 trees and any buildings.  It is very difficult to remove cultural = noise=20 as I have found.  However, you should be careful and do not = disturb any=20 more dirt than you need.  Dirt once disturbed is difficult to = re-compact=20 and will be a source of noise for a long time to come as it settles. =  I=20 have found that after 1 1/2 years, I still get occasional ground noise = from=20 settling dirt.

Another thought to consider is insulating your=20 instrument from wind currents.  Seismometers are extremely = sensitive to=20 any wind flow and temperature change.  In my setup, I first = covered my=20 instrument with sand bags, and that did a good job of insulating the=20 instrument from thermal variation and wind flow.  However, they = were hard=20 to remove from the hole, and I settled on a large bucket lined with = fiberglass=20 which sits on top of the instrument and covers it down to its base. =  I=20 have found this to be very effective and the bucket protects the = instrument=20 from both wind flow and thermal variations.  Even in a sealed = seismic=20 vault you need to protect against errant wind currents caused by = uneven=20 thermal heating of the vault as the sun moves across the = sky.

The key=20 for a quiet instrument is reduction of cultural noise and wind noise.=20  Things to consider is under a house you will most likely pick up = movement of people in the house, and tilt from the house in times of = high and=20 possibly even moderate winds.  You proximity to trees is another=20 consideration as the root structure causes ground tilt for a = considerable=20 distance.  Railroad tracks can transmit vibrations for miles. =  The=20 worst rail noise comes from diamonds where one set tracks crosses = another set=20 of tracks.  Major roads that are in poor repair with potholes and = lots of=20 semi-trailers are another source of cultural noise.......Just some = thoughts to=20 consider.

Good luck on your location wherever you choose = it.

Bob=20 Hancock


----- Original Message -----=20
 
From:  Gary  Lindgren <mailto:gel@.................>= ;=20  
 
To: psn-l@.................
 
Sent: Thursday, August 28, 2008 9:59=20  AM
 
Subject: craw space under=20 house

Hi All,=20    I am building a new house.   This = house has no=20 basement, but has a  24"? crawlspace under the house. =   I=20 have lots of time, to create a  space for my three sensors, = under the=20 house.   I could also place  them in the garage on = the=20 concrete floor.   My thought was to enter  the = crawlspace,=20 and dig a small pit large enough to allow for elbow room, then =  line=20 the pit with concrete blocks to keep dirt away.  Perhaps=20  covering the floor area similarly.  Concrete may not be = the=20 best  material.   I could also pour a pad or small = footing=20 using  cement.

 

Please any thoughts  on preparing = this=20 space?

 

 
 
 

Thanks,=20  Ted



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