Trench collapses rarely give adequate warning — but they give some. Workers and supervisors who know what to look for can identify a deteriorating excavation before it fails. The first worker to recognize distress signs and call for evacuation is the worker who saves lives. These are signs you need to recognize before you ever enter a trench.

• Tension cracks: Vertical or diagonal cracks in the soil at the edge of the excavation — the soil is beginning to separate along a potential failure plane
• Fissures: Horizontal cracks in the trench wall, especially near the base — indicates stress relief and potential base heave
• Sloughing: Small amounts of material falling from trench walls — "small" sloughing precedes larger failure
• Boiling or heaving: Soil at the bottom of the trench bubbling or rising — groundwater pressure or base failure is occurring
• Seeping water: Water entering the trench walls or bottom — softens soil rapidly and adds weight pressure

• Rain: even light rain saturates soil and dramatically changes its stability classification
• Freeze/thaw cycles: thawing soil loses cohesion it appeared to have when frozen. NYC spring thaws cause collapses daily
• Heavy equipment near the trench edge: vibration and surcharge load accelerates failure
• Adjacent construction: nearby demolition, driving, or lifting creates vibration that triggers sloughing