Q1: The design of a retaining wall assumes that the retained earth

ANS:E - all the above.

1. Is dry: While the moisture content of the retained earth can influence its properties, such as its weight and shear strength, it's uncommon for soil to remain completely dry, especially in regions with variable climates or where the water table is relatively high. Moisture content can vary due to factors such as rainfall, groundwater seepage, or nearby bodies of water. Additionally, retaining walls often encounter moisture from precipitation or irrigation, which can affect the stability and behavior of the soil behind the wall. Therefore, assuming that the retained earth is always dry may not reflect real-world conditions and could lead to underestimation of potential stability issues related to changes in moisture content.
2. Is free from moisture: Similar to the previous point, it's rare for soil to be entirely free from moisture, especially in outdoor environments. Even in arid regions, soil retains some level of moisture, either from intermittent rainfall, groundwater, or atmospheric humidity. Moisture content plays a significant role in soil behavior, affecting parameters such as cohesion, internal friction angle, and shear strength. Ignoring the presence of moisture in the retained earth could lead to inaccurate assumptions about its stability and could compromise the design of the retaining wall.
3. Is not cohesive: Cohesive soils, such as clays, exhibit cohesive properties due to the presence of fine particles that can stick together. Cohesion contributes to the shear strength of cohesive soils, making them behave differently from granular soils under load. Retaining walls constructed in cohesive soils must account for factors such as shear strength, settlement, and potential for swelling or shrinking due to changes in moisture content. Assuming that the retained earth is entirely non-cohesive overlooks the potential presence of cohesive soils, which could lead to inadequate design provisions for stability and performance.
4. Consists of granular particles: Granular soils, such as sand and gravel, are composed of individual particles that do not stick together and typically have high permeability. While granular soils may be easier to work with in retaining wall construction compared to cohesive soils, not all retained earth consists solely of granular particles. Many locations have soil profiles that contain a mixture of granular and cohesive materials, known as silty or sandy clays. These soils exhibit properties of both granular and cohesive soils and require careful consideration in retaining wall design to address factors such as drainage, shear strength, and settlement. Assuming that the retained earth consists only of granular particles may oversimplify the design process and neglect the potential challenges posed by mixed soil types.

Given these considerations, it's important for retaining wall designs to account for the specific characteristics of the retained earth, including its moisture content, cohesion, and particle composition. Ignoring these factors could lead to inadequate designs, compromised stability, and potential failure of the retaining wall. Therefore, while simplifying assumptions may be made in preliminary design stages, detailed analysis and site-specific considerations are essential for ensuring the safety and effectiveness of retaining wall structures.