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I see these things at construction sites pretty often and have no idea what they are for.
It’s about 5 feet tall, 2 feet wide, 2 feet deep, 3-inch wall thickness and hollow. Big circular indents on each side. They’re usually empty, sometimes with random litter inside.
What is its purpose?
Maybe a distribution pit? https://www.frankstonconcrete.com.au/product/300x300-distribution-pit/
The holes aren't always pre-cut because it depends on the construction / building which ones will be used, and it is easier to cut holes into those blocks as needed instead of sealing off holes that are already present.