Assignment:
1) Define or describe the following;
a) Reference state for soil water potential
b) Diffuse double layer
c) Soil bulk density
d) Soil water potential equilibrium
e) Cohesion
f) Soil water hysteresis
g) Porosity
h) Matric potential
i) Total soil water potential
j) Specific surface
k) Contact angle
l) Air entry matric potential
m) Volumetric water content
n) Time Domain Reflectometry
o) Gravimetric water content
p) Shrink-swell
q) Adhesion
r) Solute potential
s) Head units
t) Isomorphous substitution
u) Water characteristic function
2) Short answera.
a. If water exist in soil as films only (that is, water is only coating particle surfaces), explain why you would expect more water in a clay soil than in a sand.
b. As a soil drains, is it true that small diameter pores drain before larger diameter pores? Explain.
c. For a given soil, is the bulk density a constant? Explain.
d. Explain why soil water would move from a drier to a wetter soil. Or could it?
e. Does water drip from unsaturated soil? Explain based on interfacial curvature.
f. It is often said that water always flow downhill. Is this true? Explain.
g. Why do we need a reference state for the soil water potential? List the properties of the reference state.
h. Can an unsaturated sand pull water from an unsaturated clay? Briefly explain.
i. Why does free water move against gravity into narrow diameter pores?
3) Concise essay
a. Briefly describe the forces in soil which reduce the potential energy of water relative to the reference state.
b. Explain the purpose and basic operation of the pressure plate.
c. Briefly describe the principle of operation of Neutron Attenuation (neutron probe) and Time Domain Reflectometry. What do these measure and how?
d. Concisely discuss the key physical and chemical characteristics of the soil solid phase involved with the adsorption and retention of water.
e. Briefly explain why some soils change dimension (swell) upon wetting while others do not.
f. A friend suggests that you use a tensiometer for the indirect measurement of soil water content. Briefly discuss the operation of the tensiometer, what it measures, and list pros and cons of using it for measuring soil water content.
g. A certain soil is known to change dimensions with changing water content if the dominant cation in the soil is calcium but not if the dominant cation is potassium. Why?
4) Using a sketch, compare and contrast θ(h) for a fine and a coarse textured soil. Explain the similarities and differences (if any) between the curves.
5) A volume of soil (Vtotal) is the sum of the volume of pores (Vpores) and the volume of solids (Vsolids). Derive in a few steps the porosity φ expression ?? = 1 - ????/????
where ρb is the soil bulk density and ρs is the particle density.