pore water measurements in fine soils under saturated-unsaturated transitions

[Hector]

Dear Community!

We are interested in any new developments of IN-SITU pore water
measurements in fine soils under varying water levels with
saturated-unsaturated transitions. Traditionally one would assemble a
tensiometer with a porous cup of a specific air entry value. However
tensiometers need accurate maintenance to avoid recording rubbish once
air has entered the porous cup. The field installation also can be
pretty demanding due to the fragile porous cup.

We want to insert our measurement device a couple of meters into the
loamy core of a levee. There rapid water level changes occur, which can
not be recorded accurately with traditional standpipe-technique due to
the small conductivity of the core material. We are not mainly
interested in recording the suction range when the water level drops
but to accurately determine the changes in pore pressure (i. e. below
the phreatic surface) during varying water levels in the levee. Even if
there was no porous cup (no suction measurements possible) entrapped
air bubbles could affect the transducer's recording of the water
pressure.

I Would really appreciate any reports on experiences in dealing with
IN-SITU pore water measurements in fine soils under varying water
levels with saturated-unsaturated transitions?

Regards

Hector

[maison.mousse]

Hector a écrit dans le message

Post by Hector
Dear Community!
We are interested in any new developments of IN-SITU pore water
measurements in fine soils under varying water levels with
saturated-unsaturated transitions. Traditionally one would assemble a
tensiometer with a porous cup of a specific air entry value. However
tensiometers need accurate maintenance to avoid recording rubbish once
air has entered the porous cup. The field installation also can be
pretty demanding due to the fragile porous cup.
We want to insert our measurement device a couple of meters into the
loamy core of a levee. There rapid water level changes occur, which can
not be recorded accurately with traditional standpipe-technique due to
the small conductivity of the core material. We are not mainly
interested in recording the suction range when the water level drops
but to accurately determine the changes in pore pressure (i. e. below
the phreatic surface) during varying water levels in the levee. Even if
there was no porous cup (no suction measurements possible) entrapped
air bubbles could affect the transducer's recording of the water
pressure.
I Would really appreciate any reports on experiences in dealing with
IN-SITU pore water measurements in fine soils under varying water
levels with saturated-unsaturated transitions?
Regards
Hector

I'm not sure what you want to do but here are some references that may or
may not
be helpful
ASTM D5126-90, Standard Guide for Comparison of Field Methods for
Determining Hydraulic Conductivity in the Vadose Zone (ASTM 1992n).
Amoozegar,A, and A. W. Warrick. 1986. Hydraulic conductivity of saturated
soils: field methods.
American Society of Agronomy. 1986. (9,pt.1) p. 735-770. ill.
Bouwer, H. 1986. Intake Rate: Cylinder Infiltrometer. American Society of
Agronomy. 1986.
Amoozegar, A. (1992) Compact Constant Head Permeameter: A convenient Device
for Measuring Hydraulic Conductivity. Soil Science Society of America.
Advances In Measurement of Soil Physical Properties: Bringing Theory into
Practice.
Herman, S., Mertens, J., Timmerman, A., and Feyen, J. 2003. Comparison of
tension infiltrometer, single-ring pressure infiltrometer and soil core Ksat
estimates on a sandy loam hill slope. Geophysical Research Abstracts, Vol.
5, 02662, 2003.
http://web.ead.anl.gov/resrad/datacoll/conuct.htm
http://soils.usda.gov/sqi/kit2.html
http://esce.ucr.edu/soilwater/news.htm#New%20Method
http://esce.ucr.edu/WU/CETRAIN.html
http://www.sdec-france.com/us/doubleanneaux.html
http://www.uswcl.ars.ag.gov/exper/mariotte.htm

Soil Quality USDA on the web somewhere
Test Kit Guide

JOL

[b***@gmail.com]

Sorry, probably my posting was a bit ambiguous. We are looking for
In-situ measurements of pore water PRESSURE in a soil of small
conductivity under varying water level and saturation conditions.

Regards

Hector

[Hector]

Sorry, probably my posting was ambiguous. We are looking for the pore
water PRESSURE in a soil of small conductivity with varying water level
and saturation conditions

Regards

Hector

What

Post by Hector
Dear Community!
We are interested in any new developments of IN-SITU pore water
measurements in fine soils under varying water levels with
saturated-unsaturated transitions. Traditionally one would assemble a
tensiometer with a porous cup of a specific air entry value. However
tensiometers need accurate maintenance to avoid recording rubbish once
air has entered the porous cup. The field installation also can be
pretty demanding due to the fragile porous cup.
We want to insert our measurement device a couple of meters into the
loamy core of a levee. There rapid water level changes occur, which can
not be recorded accurately with traditional standpipe-technique due to
the small conductivity of the core material. We are not mainly
interested in recording the suction range when the water level drops
but to accurately determine the changes in pore pressure (i. e. below
the phreatic surface) during varying water levels in the levee. Even if
there was no porous cup (no suction measurements possible) entrapped
air bubbles could affect the transducer's recording of the water
pressure.
I Would really appreciate any reports on experiences in dealing with
IN-SITU pore water measurements in fine soils under varying water
levels with saturated-unsaturated transitions?
Regards
Hector

[maison.mousse]

Hector a écrit dans le message

Post by Hector
Sorry, probably my posting was ambiguous. We are looking for the pore
water PRESSURE in a soil of small conductivity with varying water level
and saturation conditions
Regards
Hector
What

Post by Hector
Dear Community!
We are interested in any new developments of IN-SITU pore water
measurements in fine soils under varying water levels with
saturated-unsaturated transitions. Traditionally one would assemble a
tensiometer with a porous cup of a specific air entry value. However
tensiometers need accurate maintenance to avoid recording rubbish once
air has entered the porous cup. The field installation also can be
pretty demanding due to the fragile porous cup.
We want to insert our measurement device a couple of meters into the
loamy core of a levee. There rapid water level changes occur, which can
not be recorded accurately with traditional standpipe-technique due to
the small conductivity of the core material. We are not mainly
interested in recording the suction range when the water level drops
but to accurately determine the changes in pore pressure (i. e. below
the phreatic surface) during varying water levels in the levee. Even if
there was no porous cup (no suction measurements possible) entrapped
air bubbles could affect the transducer's recording of the water
pressure.
I Would really appreciate any reports on experiences in dealing with
IN-SITU pore water measurements in fine soils under varying water
levels with saturated-unsaturated transitions?
Regards
Hector

I'm not sure what your reason is for the determination. But you may want to
look at neutron scattering technique or if you just want to measure
variation you may want to use a recording dc resistivity device. For this
check with ABEM
or a geophysical contractor in your area.

JOL

[James McKelvey Jr]

Post by maison.mousse
Hector a écrit dans le message

Post by Hector
Sorry, probably my posting was ambiguous. We are looking for the pore
water PRESSURE in a soil of small conductivity with varying water level
and saturation conditions
Regards
Hector
What

Post by Hector
Dear Community!
We are interested in any new developments of IN-SITU pore water
measurements in fine soils under varying water levels with
saturated-unsaturated transitions. Traditionally one would assemble a
tensiometer with a porous cup of a specific air entry value. However
tensiometers need accurate maintenance to avoid recording rubbish once
air has entered the porous cup. The field installation also can be
pretty demanding due to the fragile porous cup.
We want to insert our measurement device a couple of meters into the
loamy core of a levee. There rapid water level changes occur, which can
not be recorded accurately with traditional standpipe-technique due to
the small conductivity of the core material. We are not mainly
interested in recording the suction range when the water level drops
but to accurately determine the changes in pore pressure (i. e. below
the phreatic surface) during varying water levels in the levee. Even if
there was no porous cup (no suction measurements possible) entrapped
air bubbles could affect the transducer's recording of the water
pressure.
I Would really appreciate any reports on experiences in dealing with
IN-SITU pore water measurements in fine soils under varying water
levels with saturated-unsaturated transitions?
Regards
Hector

I'm not sure what your reason is for the determination. But you may want to
look at neutron scattering technique or if you just want to measure
variation you may want to use a recording dc resistivity device. For this
check with ABEM
or a geophysical contractor in your area.
JOL

I too am a little confused. The pore pressure should be the same as the
exterior load. I once measured the pressure-porosity curve for the water
Bentonite system. The derived expression put the curve through 1 MPa (145
psi) at 60% porosity and 68.6 MPa (10,000 psi) at 34% porosity.

If this is any help..your welcome

gresham

[Don Baker]

You're asking for a tough one, to measure pore water pressure directly
without a porous cup. Everything else is indirect, say, using a water
content sensor (TDR, capacitance, thermal conductivity, nuclear, etc) in
conjunction with a head/content curve. If I remember correctly, all
pressure measuring devices depend upon deflection of a diaphram in
direct contact with the water. The time constant is directly dependent
upon the flow resistance of cup AND the soil, and the amount of water
needed to get the necessary sensor deflection, which is larger for
larger sensors. Likely, to get a faster time response the only thing you
can do is to make the instrument smaller.

I would suggest looking for micro-electromechanical sensors, with a very
small the porous cup or barrier placed directly upon an integrated
circuit or surface-mount electronics board. Although they are not very
accurate, and are subject to temperature effects, you might consider
adapting commercial/automotive silicon absolute pressure sensors to your
needs with very small porous barriers and conformal coatings to protect
the electronics. You would have to fill it by pulling a hard vacuum on
it and then letting water fill the vacuum container.

I'm not sure, but you might also look at soil water dew-point sensors.
Although I think that might be more of a measure of the effect of total
water energy potential on vapor pressure.

Regards,
Don Baker, Ph.D. Soil Physics
Tulsa, OK

Post by Hector
Sorry, probably my posting was ambiguous. We are looking for the pore
water PRESSURE in a soil of small conductivity with varying water level
and saturation conditions
Regards
Hector
What

Post by Hector
Dear Community!
We are interested in any new developments of IN-SITU pore water
measurements in fine soils under varying water levels with
saturated-unsaturated transitions. Traditionally one would assemble a
tensiometer with a porous cup of a specific air entry value. However
tensiometers need accurate maintenance to avoid recording rubbish once
air has entered the porous cup. The field installation also can be
pretty demanding due to the fragile porous cup.
We want to insert our measurement device a couple of meters into the
loamy core of a levee. There rapid water level changes occur, which can
not be recorded accurately with traditional standpipe-technique due to
the small conductivity of the core material. We are not mainly
interested in recording the suction range when the water level drops
but to accurately determine the changes in pore pressure (i. e. below
the phreatic surface) during varying water levels in the levee. Even if
there was no porous cup (no suction measurements possible) entrapped
air bubbles could affect the transducer's recording of the water
pressure.
I Would really appreciate any reports on experiences in dealing with
IN-SITU pore water measurements in fine soils under varying water
levels with saturated-unsaturated transitions?
Regards
Hector