Which type of soil is defined as having an unconfined compressive strength of 0.5 tsf or less?

The correct classification for soil with an unconfined compressive strength of 0.5 tsf or less is indeed Type C. This type of soil is typically characterized as having low strength, which can influence how excavation and construction are approached to ensure worker safety.

Type C soils include materials such as silty sand, sandy silt, and clayey sand, amongst others. Their properties often lead to a greater risk of cave-ins or soil collapse if proper protective measures, such as trenching and shoring, are not enforced in construction sites.

In contrast, Type A and Type B soils have higher compressive strengths and do not possess the same level of risk associated with excavation work. Type A soils, for example, can support higher loads and resist collapse better than Type C. Type B soils, while also stronger than C, still have a compressive strength between Type A and Type C, indicating more stability than Type C but less than Type A.

It’s vital for construction professionals to understand these classifications to implement appropriate safety protocols and ensure a safe work environment on job sites.