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Soil moisture determination method
Soil Moisture Determination Method
1. Scope of Application
This standard is applicable for determining the moisture content in all types of soil, excluding gypsum soil and organic soil that contains more than 20% organic matter. It is widely used in geotechnical engineering, agricultural research, and environmental monitoring to assess soil properties accurately.
2. Principle of Measurement
The method is based on the principle that the weight loss of a soil sample after being dried at 105°C until it reaches a constant weight corresponds to the moisture content. This approach ensures accurate and reliable results by eliminating all free water from the soil sample.
3. Instruments and Equipment
- Soil corer: For collecting undisturbed soil samples.
- Sieve: With a mesh size of 1 mm to ensure uniform particle size.
- Aluminum containers: Two sizes are available—small (diameter ~40 mm, height ~20 mm) and large (diameter ~55 mm, height ~28 mm).
- Analytical balance: Capable of measuring with precision up to 0.001 g and 0.01 g.
- Electric oven: A small, constant-temperature oven for drying samples.
- Desiccator: Filled with silica gel or anhydrous calcium chloride to keep samples dry during cooling.
4. Sample Selection and Preparation
- Air-dried soil: Collect representative samples, crush them, pass through a 1 mm sieve, and mix thoroughly before use.
- Fresh soil: Take a representative sample from the field, remove surface debris, and collect approximately 20 g from the middle layer. Place it in a pre-weighed aluminum container, seal it, and transport it to the lab. Clean the container's exterior, weigh it immediately, and proceed with moisture analysis as soon as possible.
5. Measurement Procedure
- Air-dried soil: Preheat the oven to 105°C, dry the aluminum box for about 2 hours, cool it in a desiccator, and weigh it. Add about 5 g of soil, reweigh, then dry in the oven for 6 hours. Cool and reweigh. Perform two parallel tests for accuracy.
- Fresh soil: Weigh the aluminum container with fresh soil to the nearest 0.01 g. Dry it in the oven for 12 hours, cool in a desiccator, and reweigh. Conduct three replicates for better precision.
Note: Once the sample reaches a constant weight after drying, further drying will not significantly affect the results.
6. Calculation of Results
- Moisture content (on a wet basis): % = [(m₠- m₂) / (m₠- m₀)] × 100
- Moisture content (on a dry basis): % = [(m₠- m₂) / (m₂ - m₀)] × 100
Where:
- mâ‚€ = mass of the empty aluminum container (g)
- mâ‚ = mass of the container plus soil before drying (g)
- mâ‚‚ = mass of the container plus soil after drying (g)
7. Data Reporting
Results from parallel determinations should be reported as the average value, rounded to one decimal place. The acceptable difference between parallel results is:
- Less than 0.2% for air-dried soils with less than 5% moisture.
- Less than 0.3% for moist soils with 5–25% moisture.
- Less than 0.7% for coarse-grained soils with moisture content over 15%.
This method provides a standardized and repeatable approach for soil moisture analysis, ensuring consistency and accuracy in various scientific and engineering applications.