Outline
• Web page updated
• The lab (AGRON 578)
• Wikipedia stuff
• Where were we?
• Porous medium basics
Soil Physics 2010
Web page updated
Date
Reading in Reading in
official Hillel alternate
Textbook
Hillel text
Topic
Jan. 11 Introduction
Jan. 13 Soil as a porous medium
xiii – xv,
3 – 11
xix – xxv,
3–9
Jan. 15 Mass and volume relationships
12 – 17
10 – 17
Jan. 18
Soil Physics 2010
M. L. K. jr. Holiday
The lab (AGRON 578)
• Lab moved to Friday, 1:10–4:10 pm
• There is still time to enroll!
Soil Physics 2010
Wikipedia stuff
• There is a WikiProject Soil:
http://en.wikipedia.org/wiki/Wikipedia:WikiProject_Soil
• Links from the project page include:
• Article templates
• Suggested topics
• Articles needing attention
• Articles & enhancements requested by
Ecology
Soil Physics 2010
Where were we?
• What do soils do?
• What physical properties make
this possible?
• What physical processes must
occur in soils to make this
possible?
Soil Physics 2010
What physical properties are required for soil to “work”?
These
But also these
• Strong: self-supporting &
load-bearing
• Weak enough for roots to
penetrate
• Permeable to air and water
• Retaining both air and water
• Conduct water fast to
prevent erosion
• Prevent water from leaving, so
plants don’t wilt
• Lots of surface area for
reactions, microbes, etc.
• Too much surface area lowers
the permeability
• Low thermal conductivity
(moderate temps. at depth)
• High thermal conductivity
(moderate depth of extremes)
Soils don’t decide to have certain properties.
Their transport properties emerge from other properties.
Soil Physics 2010
What are the big issues in soil physics today?
My top 5:
• Heterogeneity, randomness and structure
• Scale, upscaling, downscaling, and scale
integration
• Coupled processes
• Integration with meteorology, hydrology, etc.
• Legacy of empirical, non-physical concepts
Soil Physics 2010
Porous medium basics
What is a porous medium?
A composite of solid and fluid
(liquid and/or gas)
The volume fraction of non-solid
is called the porosity (f).
Note: Hillel uses f for porosity. f is the Greek f.
Soil Physics 2010
What solids are not porous?
(few if any)
The f continuum
f=0
pure
solid
Continuous solid
impermeable
porous
medium
Caution!
Porosity isn’t the only thing
affecting continuity!
There can be fluid continuity
at just 0.1% porosity!
permeable
porous
medium
pure
fluid
suspension
Continuous fluid
In permeable media
(like soils), both the
solid and fluid are
Soil Physics 2010
f=1
continuous
The f continuum
at work
f=1
f=0
Soil Physics 2010
What does f tell us?
Not as much as we like to think: there are many kinds of f
Total Porosity
Isolated Porosity
Connected Porosity
Flowing part
Dead Ends
How you measure f determines what you measure.
Soil Physics 2010
How do you measure f?
Saturate, dry, calculate
-
=
Problems:
Miss the isolated pores
Can’t be sure all pores saturate
Can’t be sure all pores dry
Soil Physics 2010
Other methods?
Crushing
Image analysis
Different types of porous media
Fibrous:
Fiberglass insulation
Wood
Paper
Hay bale
Textiles
Foam (open-cell & closed-cell both):
Styrofoam
Expanding foam (like Great Stuff ™)
Pumice
Soap
Swiss cheese
Soil Physics 2010
Granular:
Soil
Packing peanuts
Grain in a silo
Sand & gravel
Apple
Fractured:
Fractured rock
Soil with drying cracks
Dual-porosity:
(practically all granular)
(practically all fractured)
Fibrous:
Soil Physics 2010
Filter paper
Fibrous:
Soil Physics 2010
Fibrous:
Micro-computed tomographic section through a
titanium implant in a sheep femur.
Soil Physics 2010
Fibrous (?): capillary network
Soil Physics 2010
Foam – both open-cell & closed-cell
Soil Physics 2010
Lung alveola
Soil Physics 2010
Open-cell foams
Open cell aluminum foam
Soil Physics 2010
Dry sponge swab
Open-cell foams
A 2.5 kg brick supported by
2 g of aerogel, which can
have porosity up to 99.9%
Soil Physics 2010
Closed cell foam
(Voronoi tessellation)
Soil Physics 2010
Closed cell foam (aluminum)
Soil Physics 2010
Pumice
http://www.swisseduc.ch/stromboli/glossary/
pumice-en.html
http://australianmuseum.net.au/image/Pumice
Soil Physics 2010
Fractured rock
Most porosity is not from
fractures, but almost all flow
is in fractures.
Soil Physics 2010
Soil with drying cracks
Dual-porosity:
Big pores (cracks)
Little pores (soil matrix)
Nothing in between
Soil Physics 2010
Granular: porous concrete
Soil Physics 2010
Granular: sintered metal
Soil Physics 2010
Granular: pome fruit
A to D, Tomographic images of the cortex of apple (A and C) and pear (B and D)
Verboven, P., et al. Plant
Physiol. 2008;147:518-527
Copyright ©2008 American Society of
Plant Biologists
Soil Physics 2010
3-D rendering of the void network of apple cortex
Verboven, P., et al. Plant Physiol.
2008;147:518-527
Copyright ©2008 American Society of Plant
Biologists
Soil Physics 2010
Virtual
(Granular)
Slice through
a 3D packing
model with 4
sphere sizes
Soil Physics 2010
Virtual
2D lattice
Boltzmann
model
Soil Physics 2010
Virtual
We won’t study all these strange media in this class.
But seeing a bigger range of kinds of media can keep
our thinking from getting too narrow.
Notice that porespace has both geometrical (size)
and topological (connection) components.
Soil Physics 2010
Soils are porous media
• Porosity varies widely (60% > f > 30%)
• Particle sizes vary widely (sand, clay)
• Geological and/or organic materials of varying
mineralogy and composition
• Permeability varies widely
• Granular, fractured, and/or amorphous
• Vary spatially & temporally
• Most complex & widespread biomaterial on the
planet
so it is hard to generalize!
Soil Physics 2010
Multiple scales
We concentrate here,
but sometimes it’s
useful to think about
here
Soil Physics 2010
Brian Wood
Oregon State
Irwin Fatt asked (Petr. Trans. AIME, 1956):
What are the available models for porous media?
Capillary tubes are too simplistic.
Glass beads are intractable, and they’re still too
simple.
Real porous media have multiply connected
pores (topology & connections again).
Soil Physics 2010
How do we model soil physical processes?
Soil Physics 2010