Step-by-step explanation:
(a) Effect of Water Content on Dry Unit Weight during Compaction:
1. Optimum Moisture Content (OMC): The dry unit weight of soil during compaction is influenced by its water content. When compacting a soil, the water content is adjusted to achieve the maximum dry unit weight, which occurs at a specific moisture content known as the Optimum Moisture Content (OMC). At OMC, the soil particles are well lubricated, allowing for better compaction and densification.
2. Dry of Optimum: When the water content is less than the OMC, the soil is said to be "dry of optimum." In this range, the soil is relatively dry and lacks sufficient water to promote effective particle rearrangement during compaction. As a result, the dry unit weight is lower compared to the maximum dry unit weight achieved at OMC.
3. Wet of Optimum: When the water content exceeds the OMC, the soil is considered "wet of optimum." In this range, the excess water creates a lubricating effect that reduces friction between particles. While this makes compaction easier, the excess water also creates voids, resulting in a decrease in the dry unit weight compared to the maximum value at OMC.
4. Influence on Soil Engineering Properties: The water content significantly impacts the engineering properties of compacted soil, such as its strength, permeability, and settlement characteristics. Therefore, it is crucial to determine the OMC during compaction to achieve the desired density and stability of the soil.
(b) Effect of Compaction Effort on Dry Unit Weight:
1. Increased Compaction Effort: Applying higher compaction effort, such as using heavier rollers or repeated passes during compaction, leads to increased dry unit weight. The increased effort results in greater particle rearrangement and closer packing of soil particles, reducing void spaces and increasing the overall density.
2. Optimal Compaction Effort: There is an optimum level of compaction effort beyond which additional effort may yield diminishing returns in terms of increased dry unit weight. This optimal level varies depending on soil type and gradation. It is essential to achieve compaction within this range to ensure cost-effectiveness and avoid potential damage to the soil structure.
3. Influence on Soil Properties: Higher dry unit weight achieved through increased compaction effort results in improved soil strength and stability. It also reduces permeability, making the soil less susceptible to water infiltration and potential erosion. These properties are crucial for supporting structures, minimizing settlement, and providing adequate load-bearing capacity.
4. Limitations: Extremely high compaction effort may lead to excessive compaction, causing soil particles to become overcompressed and reducing the soil's ability to drain water. Additionally, some soils, such as certain clayey soils, have a maximum achievable dry unit weight due to their inherent properties, regardless of the compaction effort applied. Therefore, it is essential to balance compaction effort with soil type and engineering requirements to achieve optimal results.