Soil Physics 2010

Outline • Announcements • Aeration • Permeability • Relative permeability • Air permeability Soil Physics 2010

Announcements • Review session Friday, 11:00 – 1:00 • Homework 5 due now • Exam II on Friday, April 2 • Remember I’ll be gone most of next week Soil Physics 2010

And now Delise, on the topic of Aeration Soil Physics 2010

Aeration mechanisms • Advection (also called convection, mass movement, mass flow) • Diffusion • We’ll look at advection today, and start diffusion on Friday. Soil Physics 2010

Advection Darcy’s law is about advection (or mass flow): Mass moved (flux density) Potential gradient Proportionality coefficient Soil Physics 2010

Now replace the water with molasses (keep the same soil, same potential gradient) Same flux? Same potential gradient Same proportionality coefficient? • Ks has 2 parts: • Soil properties • Fluid properties Soil Physics 2010

Parts of Darcy’s Ks Soil property: Permeability k L2 Fluid property: Fluidity f L-1 T-1 Fluidity is often given as r g/h: r fluid density g gravitational acceleration h fluid viscosity Soil Physics 2010

What’s with the L2? Permeability k L2 The actual length L that is squared for a soil’s permeability is quite small. It is usually interpreted as the soil’s effective pore diameter. Soil Physics 2010

Back to water, molasses, etc. Soil permeability fluidity The soil’s permeability does not depend on the fluid’s properties. So permeability can also describe the flow of air Soil Physics 2010

Relative permeability kr Big pores Little pores 1 Air permeability of dry soil = Water permeability of saturated soil kr 0 0 Sw 1 1 Sa 0 Soil Physics 2010

Relative permeability 1 Petroleum engineers, and some geologists, use these “relperm” plots kr 0 0 Sw 1 1 Sa 0 Soil Physics 2010

Air permeability ka air entry value h 0 1 No air flow until soil has dried to the air entry value. This is like qr for hydraulic conductivity: K(qr) = 0 ka 0 0 Sw 1 1 Sa 0 Soil Physics 2010

Measuring air permeability Soil Physics 2010

Soil Physics 2010