What can be said about a layer that is stable for unsaturated conditions?

A layer that is stable under unsaturated conditions can indeed become unstable when saturated. This phenomenon occurs because the introduction of water can alter the physical properties of the soil or material layers, such as pore pressure and cohesion, which are critical factors in determining stability. When a layer is unsaturated, the soil particles are held together effectively through capillarity, providing stability. However, when the soil becomes saturated, the water fills the pores and can reduce the effective stress acting on the soil particles, leading to potential failures like landslides or slope failures.

Recognizing that a stable layer in unsaturated conditions may not retain that stability once it becomes saturated is fundamental in fields such as geotechnical engineering and earth sciences. This understanding is crucial for assessing slope stability, designing retaining structures, and predicting landslide risks during rainy conditions.