In what scenario would soil be classified as unstable during excavation?

Soil becomes classified as unstable particularly when it becomes waterlogged. When soil is saturated with water, it loses its cohesion and internal friction, which are critical attributes for maintaining stability. This can lead to an increased risk of landslides, collapse, or other hazards during excavation activities. The presence of excess water reduces the weight of the soil particles pressing against one another, thereby heightening the potential for shifting or sliding, especially under load.

In the context of excavation safety, recognizing waterlogged soil is essential for implementing proper safety measures. Guidelines may dictate that additional support systems, like shoring or bracing, be put in place to prevent cave-ins when such conditions are present. Thus, a waterlogged state is a clear indicator of instability and a vital consideration for safe excavation practices.