Why do excavation cave-in situations necessitate the use of additional backfill?

Fallen materials from a cave-in often cannot be reused as backfilling due to contamination or disruption of their structure, making them unsuitable for stabilizing the excavation site. When a cave-in occurs, the materials that collapse into the excavation typically lose their integrity and may have been contaminated by fuels, chemicals, or other hazardous substances present in the soil or from the excavated materials themselves. Therefore, additional backfill is often required to fill in the space left by the cave-in and to ensure the excavation remains safe for workers.

While other factors, such as stabilizing surrounding soil and preventing water accumulation, play significant roles in managing excavation sites, the condition of the fallen materials is critical in determining whether existing soil can be reused. Thus, using additional backfill is essential for maintaining site safety and integrity, especially after an incident of cave-in.