What term refers to soil that has sunk on the horizontal surface of the excavation?

The term that describes soil that has sunk on the horizontal surface of the excavation is "subsidence." Subsidence refers to the gradual settling or sinking of the ground's surface, often resulting from the removal of water, the compaction of soil, or the collapse of underground structures. In the context of an excavation, if the soil around or beneath the area settles or sinks, it can lead to issues such as structural instability or surface cracking.

Understanding subsidence is crucial for contractors and engineers, as it can affect the foundation and overall integrity of any structures built on or near the affected area. Proper planning and assessment are necessary to mitigate the risks associated with subsidence during construction projects.