What is one of the assumptions of Rankine's theory regarding soil-wall interaction?

One of the key assumptions of Rankine's theory concerning soil-wall interaction is that there is no friction between the wall and the soil. This means that the soil can exert its lateral pressure on the wall without any resistance caused by friction between the two materials. This assumption simplifies the calculations associated with lateral earth pressure because the analysis can focus solely on the pressure from the soil without accounting for additional forces due to friction.

Rankine's theory is designed to calculate lateral earth pressures under conditions where it assumes a retaining wall is either vertical or slightly inclined, and it operates under the premise that any wall is smooth enough to avoid friction effects. This is crucial for determining the active and passive earth pressures acting on the wall.

Understanding this assumption allows engineers to derive fundamental equations governing soil pressures, facilitating more effective design and analysis of structures such as retaining walls. The lack of friction consideration helps delineate between active earth pressure states from passive pressure states, leading to clearer insights in geotechnical engineering applications.