Although sand is a solid, did you know it can behave like a liquid? Find out how by trying this activity.
You will need
- A brick
- A large plastic container
- A rolling pin
What to do
- Fill the container almost to the top with sand.
- Carefully push the end of the brick into the sand so that it stands up.
- Quickly and gently tap the side of the container with the rolling pin. What happens?
- Pour water into the container until it’s just below the surface of the sand.
- Tap the side of the container with the rolling pin again. What happens now?
The sand particles pack together closely but not completely: they leave gaps. When you add water it fills these gaps. The sand still behaves as a solid but it is said to be saturated.
When you tap the side of the container, the vibrations squeeze the sand particles together. The water doesn’t have enough time to move out of the way, so the water pressure increases. The water pressure pushes the sand particles away from each other. The sand particles no longer push together and instead start to float. The sand now acts as a liquid. This process is known as liquefaction.
This phenomenon can occur on a large scale. When an earthquake occurs, the tremors can cause liquefaction of soil. Buildings situated on top of this soil become highly unstable and may collapse or sink into the ground. Recent earthquakes in Christchurch caused widespread liquefaction which damaged many buildings.
Engineers and architects need to take the risk of liquefaction into account when they design buildings. The foundations of the building may need to be strengthened, or drainage systems put in place to prevent the soil becoming saturated.
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