For safety reasons, what must be done to walls of trenches deeper than 60 inches?

When dealing with trenches that exceed a depth of 60 inches, safety measures are crucial to prevent cave-ins, which can be extremely dangerous and even fatal. Shoring devices are specifically designed to provide structural support to the walls of a trench, preventing soil collapse while workers are present within or near the excavation.

Using shoring methods, such as trench boxes or other bracing systems, ensures that the trench walls remain stable even under the pressure of surrounding soil. This is particularly important for deeper trenches, as the risk of collapses increases with depth, especially in areas with loose or unstable soil conditions.

Other options do not effectively address the potential hazards associated with deep trenches. For instance, filling with gravel may not provide the required support to prevent soil movement. Covering with netting does not provide structural integrity and could still allow for dangerous conditions. Similarly, marking with warning signs, while helpful for public awareness, does not mitigate the actual risks posed by unstable trench walls. Therefore, the use of shoring devices is the most appropriate and effective safety measure for trenches deeper than 60 inches.