(Fetter p235, 2) A soil sample is collected and taken to the lab. The volume of the sample is 75 cm3. At the natural water content, the sample weighs 168.00 g. It is then saturated with water and reweighed. The saturated weight is 171.25 g. The sample is dried in an oven; the dry weight is 157.22 g. Assume the density of water is 1.00 g/cm3. Find each of the following.
(a). Volumetric water content
(b). Saturation
(c). Porosity
To find the answers to the given questions, we need to understand a few concepts related to soil properties.
(a) The volumetric water content (θ_v) is a measure of the amount of water present in a soil sample as a volume fraction. It can be calculated using the following formula:
θ_v = (V_w / V_s) * 100
where θ_v is the volumetric water content, V_w is the volume of water, and V_s is the total volume of the soil sample.
In this case, the volume of the soil sample (V_s) is given as 75 cm3. To find the volume of water (V_w), we need to calculate the difference between the saturated weight and dry weight in terms of water volume.
Step 1: Calculate the water volume:
V_w = (saturated weight - dry weight) / density of water
Substituting the given values:
V_w = (171.25 g - 157.22 g) / 1.00 g/cm3
Solve for V_w.
Step 2: Calculate the volumetric water content:
θ_v = (V_w / V_s) * 100
Substitute the calculated V_w and V_s values to find θ_v.
(b) Saturation (S) represents the degree to which the pores in the soil are filled with water. It can be calculated using the formula:
S = (θ_v / θ_s) * 100
where S is the saturation, θ_v is the volumetric water content, and θ_s is the volumetric saturation.
Volumetric saturation (θ_s) can be calculated by dividing the volume of water (V_w) by the total volume of the soil sample (V_s) and multiplying it by 100.
θ_s = (V_w / V_s) * 100
Substitute the values obtained in step 1 and step 2 to find θ_s.
Then, substitute the calculated values of θ_v and θ_s into the formula to find S.
(c) Porosity (n) is a measure of the void space available in a soil sample. It can be calculated using the formula:
n = (V_voids / V_s) * 100
where n is the porosity, V_voids is the volume of voids or air space, and V_s is the total volume of the soil sample.
The volume of voids can be calculated by subtracting the dry weight of the soil sample (which includes solids and water) from the total volume of the soil sample.
V_voids = V_s - dry weight
Substitute the given V_s value and the calculated V_voids value into the formula to find n.
By following these steps and performing the necessary calculations, you can find the values for (a) volumetric water content, (b) saturation, and (c) porosity.