Final answer:
The spoil pile should be placed 8 diameters side-to-side and 15 diameters deep away from the edge of the trench for safety and stability.
Step-by-step explanation:
When it comes to trench excavation, the distance between the edge of the trench and the spoil pile is determined by guidelines to ensure safety and stability. According to newer recommendations, the spoil pile should be placed as much as 8 diameters side-to-side (the width of the trench) and 15 diameters deep (the depth of the trench) away from the edge of the trench. This helps prevent the spoil pile from collapsing into the trench and causing potential hazards.