Final answer:
Type C soil is rated below 0.5 TSF, which is the weakest and least stable soil classification used in trenching and excavation engineering.
Step-by-step explanation:
The rating of Type C soil in terms of Tons per Square Foot (TSF) is considered to be below 0.5 TSF. This classification is used in the field of engineering, specifically when assessing the safety and stability of trenches and excavations as per the standards set by the Occupational Safety and Health Administration (OSHA). Type C soil is rated below 0.5 TSF, which is the weakest and least stable soil classification used in trenching and excavation engineering.