What typically varies depending on the height and length of the wall in manholes?

The thickness of the manhole walls is determined by various factors, including the height and length of the wall. As the height increases, the walls must be thicker to withstand the additional pressure and weight from the soil above and any traffic loads that may occur on the surface. This is crucial for structural integrity and safety, ensuring that the manhole can sustain external forces without collapsing or failing. The design of manholes requires careful consideration of these variables to ensure they meet building codes and performance standards.

Other elements, such as the width of the manhole, the depth, and the type of cover used, are influenced more by the intended use, requirements for access, and specific site conditions rather than directly relating to the height and length of the wall. Thus, they do not typically vary in the same way that wall thickness does in relation to changes in wall dimensions.