soil physics 2010 outline quiz 2 answers finishing up particle sizes particle size distributions...
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Soil Physics 2010
Outline
• Quiz 2 answers
• Finishing up particle sizes
• Particle size distributions
• Clay
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Soil Physics 2010
Quiz 2 answers
Water rises higher in a capillary tube with a (larger / smaller) interior diameter.
Water is (more / less) viscous when it is hot.
A mineral salt (e.g., NaCl) will dissolve more readily in a liquid with a (low / high) dielectric permittivity.
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Soil Physics 2010
Measuring soil particle sizes: Sedimentation
9
2 2grv ws
Assumptions:
Particles are smooth spheres
Particles fall slowly (laminar flow)
All particles have the same density
Dilute: particles don’t affect each other
Fluid is otherwise at rest
Terminal velocity is reached instantly
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Soil Physics 2010
Volume?Surface area?Projected area?Longest transect?Largest inscribed sphere?Smallest circumscribed sphere?Largest circle inscribed in projection?Smallest circle circumscribing projection?…?
What is the “equivalent sphere” in Stokes settling?
Measuring soil particle sizes: Sedimentation
90%
70%
40%
After Matthews, 1991
Settling velocity, % of sphere
Oblate(lentil)
Prolate(rice)
What are the effects of roughness & shape?
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Measuring soil particle sizes: Laser diffraction
Small particle Large particle
Soil Physics 2010
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Measuring soil particle sizes: Laser diffraction
Soil Physics 2010
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Measuring soil particle sizes: Laser diffraction
Soil Physics 2010
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Measuring soil particle sizes: Laser diffraction
FastNo calibrationWide size rangeGood repeatabilityExpensive equipment
Soil Physics 2010
Equivalent radius?
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Soil Physics 2010
Measuring soil particle sizes: Image analysis
Volume?Surface area?Projected area?Longest transect?Feret diameter?Sauter mean diameter?Largest inscribed sphere?Smallest circumscribed sphere?Largest circle inscribed in projection?Smallest circle circumscribing projection?…?
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Soil Physics 2010
Particle size distributions
Sand Silt Clay
Start with a continuum of sizes…
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Soil Physics 2010
Particle size distributions
Break it in half * and bend it over…
Sand Silt
Clay
* about halfway on a log scale
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Soil Physics 2010
Particle size distributions
…and you have the “texture triangle”
Quick and easy, but not really a
distribution
Sand
Silt
Clay
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About size distributions
Soil Physics 2010
Calculated by: Mass?
Volume? Number?
Do we assume some mathematical model?
What use is this distribution?PedologyFert/ChemHydrology
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Soil Physics 2010
Distributions?
?!?
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Cumulative distributions
0.0
0.2
0.4
0.6
0.8
1.0
0 2 4 6 8
Cumul., 0.5
0.5
Cumul., 1.0
1
Soil Physics 2010
% depends on bin size
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Soil Physics 2010
0
0.005
0.01
0.015
0.02
0.025
0.0
0.2
0.4
0.6
0.8
1.0
1 10 100 1000 10000
Series1
Series2
0.0001
0.001
0.01
0.0
0.2
0.4
0.6
0.8
1.0
1 10 100 1000 10000
Series1
Series2
0
0.001
0.002
0.003
0.004
0.005
0.0
0.2
0.4
0.6
0.8
1.0
1 10 100 1000 10000
Series1
Series2
0.000001
0.00001
0.0001
0.001
0.01
0.1
0.0
0.2
0.4
0.6
0.8
1.0
1 10 100 1000 10000
Series1
Series2
equal spacing in linear space≠
equal spacing in log space
Cumulative graph stays the same
Cumulative distributions
Variable bin size?!
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Displaying particle size distributionsCumulative distribution must be
Continuous & Monotonic
Usually shown as:Log x-axis (size)
Linear y-axis (%)
?
Soil Physics 2010
SievingSt
okes
set
tling ?
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10110010-110-210-310-4
More particle size distributions
Soil Physics 2010
GradualAbruptPoorly graded
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Clay
Soil Physics 2010
Kaolin:“china clay” from Chinese Kao-ling, transliteration of the name of a mountain in Jiangxi, China (near which it was originally dug up), from Chinese gao “high” + ling “mountain, hill.”
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Soil Physics 2010
Key things about clay
Small< 2 m
Secondary mineralplaty shape
Large surface area
Soil strength & structurePorosity & permeability