Why might ground conditions appear stable but not be so?

Ground conditions may seem stable due to previous excavation work because this type of activity can alter the structural integrity of the soil. When excavation occurs, it often disturbs the natural layers of the earth, which can lead to issues like loose soil, voids, or changes in drainage patterns. As a result, even if the ground looks solid on the surface, it may not have the necessary support or cohesion beneath it, making it unstable and prone to collapse or shifting when subjected to loads or movement.

In contrast, other factors like rainwater accumulation or surface vegetation may affect ground stability but in different ways. Rain can saturate soil, increasing the risk of instability, while vegetation may mask underlying issues without truly stabilizing the ground. Chemical treatments can also alter soil properties, but these changes differ significantly from those caused by excavation. Overall, past excavation work directly impacts the underlying soil structure, highlighting why this option is particularly relevant in assessing ground stability.