What is the effect of moisture on moist unit weight during soil compaction?

• A. Decreases the moist unit weight
• B. Increases the moist unit weight
• C. Does not affect the moist unit weight
• D. Only affects the specific gravity

Answer: (B)

The moist unit weight of soil is influenced by the moisture content present in the soil, particularly during the compaction process. When water is added to soil, it plays a crucial role in the compaction process.

As moisture content increases, the water fills the voids between soil particles and helps to lubricate the particles, allowing them to move closer together under applied compactive effort. This leads to a denser arrangement of particles and consequently increases the moist unit weight of the soil. The presence of moisture effectively increases the weight of the soil per unit volume because the water adds additional mass.

Moreover, the increased moisture can enhance the soil's ability to achieve optimum level compaction, which typically occurs at a specific moisture content known as the optimum moisture content. At this optimal level, the maximum dry unit weight is achieved.

In essence, adding moisture facilitates the compaction process, resulting in an increased moist unit weight due to the added weight of the water and the denser packing of soil particles. This interplay of moisture and compaction creates the conditions necessary to enhance the overall density of the soil, thus validating the understanding that moisture increases the moist unit weight.