Why Are Beach Holes So Deadly?

Summary by Krater

This video explains the geotechnical engineering science of slope stability, exploring why sand holes on beaches can be dangerously unstable due to shear strength, moisture, and capillary action.

From the video

Answers: Why are sand holes on the beach dangerous and how do they collapse?

• slope stability
• geotechnical engineering
• shear strength
• angle of repose
• capillary action in sand
• soil dilatancy
• trench safety guidelines

What it concludes

• Sand holes on beaches pose a fatal hazard that claims on average two to three lives per year in the United States.
• Dry sand on a flat surface is stable, but adding a slope creates shear stress that can trigger a shear failure along a circular arc.
• Moisture creates capillary action in sand, generating negative pressure that pulls particles together and increases shear strength, but this effect has limits.
• Well-packed sand undergoes dilatancy when sheared, expanding in volume and increasing strength temporarily until particles lose interlock.
• OSHA guidelines recommend sloping trench walls to 1 1/2 to 1 (about 34 degrees above horizontal) for safety in deep excavations.