Book 24, Question 142
Why can a deep hole in the sand cave in?
Dry or wet sand has no glue to hold the grains together, so the walls of a hole can slump. Sand is also heavy, and a collapse can trap a person. Keep holes at the beach or sandbox small, no deeper than your knees, and never dig tunnels. Always fill your hole in before you leave, so others and animals can't trip.
More fun facts
- Cave-ins are the greatest danger to the lives of people working in trenches.
- Sand is a granular soil, which means it has no real strength to stick together.
- Granular soil crumbles easily when dry and cannot be molded when moist.
- Some moist sand only seems to stick together, which safety rules call apparent cohesion.
- Clay soil is cohesive, so it can often be dug with straight up and down sides.
- Safety rules put sand and gravel in Type C soil, the same class as soil with water freely seeping out of it.
- In Type C soil, a sloped wall can be no steeper than 1.5 feet across for every 1 foot down.
Questions kids ask
Is wet sand safer to dig in than dry sand?
Not really. Sand has no true sticking strength, and soil with water seeping out of it is put in the same risky Type C class.