Chapter 3

Particle Density

weighted average density of the mineral grains making up a soil ps = ms/ vs (mass and volume of mineral grains)

Does bulk density increase with compaction and depth?

yes

Methods for measuring bulk density

Excavation Method In this method, a hole is dug and all of the removed soil is retained and weighed. The volume of the hole is determined by placing a plastic bag/balloon in the hole and filling it with water/air until it is flush with the surface. Clod Method In this method, a soil sample is taken and coated with a substance such as paraffin that prevents water from entering the clod. This clod is then weighed and the amount of water displaced by the clod is equal to its volume. Radiation Method In this method, gamma radiation is emitted at a known rate and the rate at which this radiation is transmitted through or reflected is related to the density of the surrounding soil.

Particle density

mass over volume Assumed at constant value of 2650 kg m-3

Porosity

proportion of pore spaces in a soil; p = va + vw / vt Fine soils have higher porosities than course soils. Clay has higher porosity than sand

soil water content and degree of saturation or wetness

soil water content = vw / vt proportion of the pores filled with water (saturation) = vw / va + vw

hydraulic conductivity

the rate at which water moves through a soil or porous medium

soil water field capacity

water content once a soil is fully saturated and has been allowed to drain

How do you measure soil water content?

1) neutron moisture meter 2) time-domain reflectometry probe 3) Microwave remote sensing -- active sensors or passive sensors

Bulk Density

Bulk density tells us the mass of the solid relative to the total volume of the soil.

What are the three means for measuring bulk density?

Excavation, clod and radiation Excavation Method In this method, a hole is dug and all of the removed soil is retained and weighed. The volume of the hole is determined by placing a plastic bag/balloon in the hole and filling it with water/air until it is flush with thesurface. Clod Method In this method, a soil sample is taken and coated with a substance such as paraffin that prevents water from entering the clod. This clod is then weighed and the amount of water displaced by the clod is equal to its volume. Radiation Method In this method, gamma radiation is emitted at a known rate and the rate at which this radiation is transmitted through or reflected is related to the density of the surrounding soil.

Describe the relationship between bulk density and pore space/porosity

Increased bulk density = lower porosity, less capacity for air and water to travel through soil. Decreased bulk density = higher porosity and capacity for air and water to travel through soil

Determining volumetric soil water content, as a fraction

To determine the solution to this problem, we can use the following formula: 0v = S n S = degree of saturation - 80% n = porosity = 0.45 cc/cc 0v = 80% * 0.45 = 0.36

Bulk Density

Weight of soil in a given volume

Explain the relationship between gravity and tension in soil water movement

When water movies into a pore, gravity and tension forces work together. Gravity pushes water into the pore, and tension pulls it into the pore. When a pore drains, gravity and tension forces oppose one another.

hysteresis

an observable effect between soil water and soil suction during drying and wetting; water content in soil is controlled by the widest point between pores, smallest pores fill first b/c they exert tension

darcy's law

describes flow of water in an unsaturated porous material