What is typically the primary factor in determining the earth pressure against a retaining wall?

The primary factor in determining the earth pressure against a retaining wall is the friction angle of the soil behind the wall. The friction angle plays a crucial role in how the soil interacts with the wall and directly affects the lateral earth pressure exerted on it.

When considering the forces at play, earth pressure is influenced by both the weight of the soil and how the soil particles interlock and slide past each other, which is quantified by the friction angle. A higher friction angle can reduce the lateral pressure because the soil has a greater ability to resist movement, leading to a decrease in the horizontal force that the wall must withstand.

Other factors, such as the height of the wall and the moisture content of the soil, can indeed impact earth pressure but are secondary in this context. The height contributes to the total weight of the soil, and moisture content affects soil cohesion and weight, both of which are less directly related to the resistance provided by the friction angle. The weight of the soil directly above the wall is also a consideration in overall load calculations but does not describe how the soil pressure is calculated, which focuses more on the interaction angle rather than just the weight itself. Thus, the friction angle stands out as the primary determinant of the lateral pressures experienced by the