What is NOT a common cause of trench and excavation cave-ins?

Sloping the sides to the angle of repose is not a common cause of trench and excavation cave-ins; rather, it is a method employed to prevent them. The angle of repose is the steepest angle at which a sloped surface is stable, and sloping the sides of an excavation at or below this angle can significantly reduce the risk of a cave-in. This technique allows the earth to support itself more effectively compared to vertical walls, thereby enhancing safety for workers in and around the excavation site.

In contrast, factors such as soil type, water accumulation, and equipment weight can all contribute to the instability of trench walls, increasing the likelihood of cave-ins. For instance, certain soil types are more prone to collapse, water can saturate the soil and reduce its strength, and the weight of heavy equipment can exert additional pressure on trench walls. Sloping, on the other hand, mitigates these risks rather than being a cause for them.