The specific gravity of organic soil is typically below 2.0, often ranging lower than that of mineral soils.
This lower specific gravity is due to the presence of organic matter, which is less dense than mineral components. Here's a breakdown:
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Specific Gravity Definition: Specific gravity is the ratio of the density of a substance to the density of a reference substance, typically water. For soils, it represents the ratio of the density of the soil solids to the density of water.
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Mineral Soil vs. Organic Soil: Mineral soils generally have specific gravity values ranging from 2.65 to 2.85. These values are influenced by the types of minerals present (e.g., quartz, feldspar). Organic soils, on the other hand, contain significant amounts of decomposed plant and animal matter, which has a lower density than most minerals.
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Factors Influencing Specific Gravity in Organic Soils:
- Organic Matter Content: The higher the organic matter content, the lower the specific gravity.
- Decomposition Stage: Partially decomposed organic matter might have a slightly higher specific gravity than highly decomposed organic matter.
- Mineral Contamination: Some organic soils may contain mineral particles, which can slightly increase the specific gravity.
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Why is Specific Gravity Important? Knowing the specific gravity is important for calculating other soil properties such as void ratio, porosity, and dry unit weight, which are used in geotechnical engineering and soil science for various applications, including:
- Soil classification: Helps in differentiating between different types of soil.
- Settlement analysis: Essential for predicting the settlement of structures built on soil.
- Compaction control: Used to determine the degree of compaction achieved during construction.
- Hydraulic conductivity estimation: Useful in assessing water flow through soils.
In summary, organic soils exhibit lower specific gravity values compared to mineral soils because of the presence of less dense organic material. This value is crucial in many geotechnical and environmental calculations.
