What specific characteristic of a soil sample indicates that it is Type C soil, according to OSHA excavation standards?

According to OSHA (Occupational Safety and Health Administration) excavation standards (29 CFR 1926 Subpart P), a specific characteristic of a soil sample that indicates it is Type C soil is that it is cohesive soil with an unconfined compressive strength of 0.5 tons per square foot (tsf) or less, or it is granular soil (including gravel, sand, and loamy sand), or it is submerged soil, or it is soil from which water is freely seeping, or it is unstable rock. Type C soil is the least stable type of soil and requires the most protective measures in excavation work. The unconfined compressive strength is a measure of the soil's ability to withstand pressure without collapsing. A low compressive strength indicates that the soil is weak and prone to cave-ins. Granular soils, such as sand and gravel, lack cohesion and are therefore classified as Type C. Submerged soil or soil with freely seeping water is also considered Type C because the water reduces the soil's strength and stability. Unstable rock is also classified as type C. OSHA regulations require specific sloping or shoring systems for excavations in Type C soil to prevent cave-ins. For example, if a soil sample crumbles easily and has a compressive strength less than 0.5 tsf, it is likely Type C soil, and the excavation must be sloped at a flatter angle (typically 1.5H:1V or 34 degrees from the horizontal) or shored to protect workers. Properly identifying soil type is crucial for ensuring worker safety in excavation operations.