Soil Physics 2010 Outline Web page updated The lab (AGRON 578) Wikipedia stuff Where were we? Porous medium basics.

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?