Embed Size (px)
Citation preview
Soil Physics 2010
Outline
• Web page updated
• The lab (AGRON 578)
• Wikipedia stuff
• Where were we?
• Porous medium basics
Soil Physics 2010
Date TopicReading in
official Hillel Textbook
Reading in alternate Hillel text
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 M. L. K. jr. Holiday
Web page updated
Soil Physics 2010
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”?
• Strong: self-supporting & load-bearing
• Permeable to air and water
• Conduct water fast to prevent erosion
• Lots of surface area for reactions, microbes, etc.
• Low thermal conductivity (moderate temps. at depth)
• Weak enough for roots to penetrate
• Retaining both air and water
• Prevent water from leaving, so plants don’t wilt
• Too much surface area lowers the permeability
• High thermal conductivity (moderate depth of extremes)
These But also these
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 ().
Note: Hillel uses f for porosity. is the Greek f.
What solids are not porous?(few if any)
= 0 = 1purefluid
puresolid
suspension
impermeableporous
medium
permeableporous
medium
In permeable media (like soils), both the
solid and fluid are continuous
Continuous solid
Continuous fluid
Soil Physics 2010
The continuum Caution!Porosity isn’t the only
thing affecting continuity!There can be fluid
continuity at just 0.1% porosity!
The continuumat work
= 0
= 1
Soil Physics 2010
What does tell us?
Not as much as we like to think: there are many kinds of
Dead EndsFlowing part
Isolated Porosity Connected Porosity
How you measure determines what you measure.Soil Physics 2010
Total Porosity
How do you measure ?
Saturate, dry, calculate
- =
Problems:Miss the isolated poresCan’t be sure all pores saturateCan’t be sure all pores dry
Other methods?CrushingImage analysis
Soil Physics 2010
Fibrous:Fiberglass insulationWoodPaperHay baleTextiles
Granular:SoilPacking peanutsGrain in a siloSand & gravelApple
Foam (open-cell & closed-cell both):StyrofoamExpanding foam (like Great Stuff ™)PumiceSoapSwiss cheese
Fractured:Fractured rockSoil with drying cracks
Dual-porosity:(practically all granular)(practically all fractured)
Different types of porous media
Soil Physics 2010
Filter paperFibrous:
Soil Physics 2010
Fibrous:
Soil Physics 2010
Micro-computed tomographic section through a titanium implant in a sheep femur.
Fibrous:
Soil Physics 2010
Fibrous (?): capillary network
Soil Physics 2010
Soil Physics 2010
Foam – both open-cell & closed-cell
Lung alveola
Soil Physics 2010
Open cell aluminum foam
Dry sponge swab
Open-cell foams
Soil Physics 2010
A 2.5 kg brick supported by 2 g of aerogel, which can
have porosity up to 99.9%
Open-cell foams
Soil Physics 2010
Closed cell foam(Voronoi tessellation)
Soil Physics 2010
Closed cell foam (aluminum)
Soil Physics 2010
http://australianmuseum.net.au/image/Pumice
http://www.swisseduc.ch/stromboli/glossary/pumice-en.html
Pumice
Soil Physics 2010
Fractured rock
Soil Physics 2010
Most porosity is not from fractures, but almost all flow is in fractures.
Soil with drying cracks
Soil Physics 2010
Dual-porosity:Big pores (cracks)Little pores (soil matrix)Nothing in between
Granular: porous concrete
Soil Physics 2010
Granular: sintered metal
Soil Physics 2010
Copyright ©2008 American Society of Plant Biologists
Verboven, P., et al. Plant Physiol. 2008;147:518-527
A to D, Tomographic images of the cortex of apple (A and C) and pear (B and D)
Granular: pome fruit
Soil Physics 2010
Copyright ©2008 American Society of Plant Biologists
Verboven, P., et al. Plant Physiol. 2008;147:518-527
3-D rendering of the void network of apple cortex
Soil Physics 2010
Slice through a 3D packing model with 4 sphere sizes
Virtual(Granular)
Soil Physics 2010
2D lattice Boltzmann
model
Virtual
Soil Physics 2010
Virtual
Soil Physics 2010
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.
Soils are porous media
• Porosity varies widely (60% > > 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
Brian WoodOregon State
Multiple scales
Soil Physics 2010
We concentrate here,but sometimes it’s useful to think about here
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
Soil Physics 2010
How do we model soil physical processes?
