How many inches of cover must be above the top of a pipe in a trench?

The correct answer is based on commonly accepted engineering practices regarding pipe installation. A cover of 24 inches above the top of a pipe in a trench is typically required to provide adequate protection against external loads, prevent damage from equipment traffic, and ensure proper soil stability. This depth helps distribute the weight from above and minimizes the risk of soil collapse into the trench, which could potentially damage the pipe or create safety hazards.

Moreover, this cover depth is particularly relevant in areas where the ground may be disturbed or where there is a high likelihood of vehicular or pedestrian traffic. Covering the pipe sufficiently helps to prolong its lifespan and maintain infrastructure integrity.

The incorrect options suggest lesser covers, which may not provide the necessary protection under typical conditions encountered in trenching for pipes. Insufficient cover could expose pipes to risks that the 24-inch requirement is designed to mitigate.