What is the definition of moisture content in soil?

Moisture content in soil is defined as the ratio of the weight of water present in the soil to the weight of the solid particles. This measurement helps determine how much water is held by the soil compared to its dry weight, providing insight into the soil's physical properties, behavior, and suitability for various engineering applications. The moisture content is usually expressed as a percentage, allowing engineers and geotechnicians to assess the water-retention capability of the soil, which is crucial for understanding drainage, compaction, and other hydrological aspects.

The other options do not accurately define moisture content, as they refer to different soil characteristics. The volume of air in the soil relates to void space but does not incorporate water measurement. The volume of water to the volume of voids indicates porosity rather than moisture content. The degree of soil compaction pertains to the arrangement of soil particles and their density, which is not directly about the presence of moisture. Understanding these distinctions is vital for properly assessing soil behavior in various engineering contexts.