Under what circumstances is over-excavation warranted and how is it treated?

• A. When subgrade is suitable and uncontaminated; leave as-is
• B. When the project requires more fill; do nothing to subgrade
• C. When subgrade is unsuitable or contaminated; remove and replace with stable material and compact to spec, sometimes with a deeper subgrade
• D. Over-excavation is never warranted; always fills are placed on top

Answer: (C)