Heaving or boiling at the bottom of an excavation is an indication of imminent _______.

• A. failure
• B. stability
• C. settlement
• D. drainage

Answer: (A)

Heaving or boiling at the bottom of an excavation shows the soil mass is losing its ability to support the loads, meaning the shear strength has been exceeded and a cave-in is imminent. It’s a direct indicator of instability in the trench, not a gradual process like settlement, nor primarily a drainage issue. So the best fit is failure.