Practical & calculations

Question 1

How do you calculate

Volumetric water content

Answer 1

θ_v = V_water/V_total

Question 2

True or False?

Expressing soil water content as volumetric water content is the best. Explain.

Answer 2

False.

The volumetric water content varies with soil compaction, making it unsuitable for lab measurement and especially for swelling soils because the volume of soil varies with water content. (Using the ratio of volume of water to soil mass is better for such soils).

Question 3

Convert a volumetric water content of 0.21 (21%) to a depth equivalent

Answer 3

21% = 210mm/m

Generally expressed in mm.

e.g. if a topsoil is 10 cm thick and has a volumetric water content 0.21, then the soil contains an equivalent depth of 21mm

Question 4

How do you calculate

Bulk density

Answer 4

ρ_b = m_{dry soil} / V_total

Question 5

True or False?

Expressing soil water content as gravimetric water content is the best. Explain.

Answer 5

True.

• Easier to determine accurately in a lab
• Independant of bulk density

Question 6

Explain the relationship between density and volume (in terms of calculations)

Answer 6

density = mass / volume

volume = mass / density

Question 7

How do you calculate

Porosity

Answer 7

Porosity, ℇ

= V_pores / V_total
= (V_total - V_solids) / V_total
= 1 - (V_solids / V_total)
= 1 - ρ_b / ρ_s