Presentation on theme: "Soil Physics 2010 Outline Web page updated The lab (AGRON 578) Wikipedia stuff Where were we? Porous medium basics."— Presentation transcript:
Soil Physics 2010 Outline Web page updated The lab (AGRON 578) Wikipedia stuff Where were we? Porous medium basics
Soil Physics 2010 DateTopic Reading in official Hillel Textbook Reading in alternate Hillel text Jan. 11Introduction Jan. 13Soil as a porous medium xiii – xv, 3 – 11 xix – xxv, 3 – 9 Jan. 15Mass and volume relationships 12 – 1710 – 17 Jan. 18M. 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 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 = 1 pure fluid pure solid suspension impermeable porous medium permeable porous 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 continuum at work = 0 = 1 Soil Physics 2010
What does tell us? Not as much as we like to think: there are many kinds of Dead Ends Flowing part Isolated PorosityConnected Porosity How you measure determines what you measure. Soil Physics 2010 Total Porosity
How do you measure ? Saturate, dry, calculate - = Problems: Miss the isolated pores Can’t be sure all pores saturate Can’t be sure all pores dry Other methods? Crushing Image analysis Soil Physics 2010
Fibrous: Fiberglass insulation Wood Paper Hay bale Textiles Granular: Soil Packing peanuts Grain in a silo Sand & gravel Apple Foam (open-cell & closed-cell both): Styrofoam Expanding foam (like Great Stuff ™) Pumice Soap Swiss cheese Fractured: Fractured rock Soil with drying cracks Dual-porosity: (practically all granular) (practically all fractured) Different types of porous media 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 Wood Oregon 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