You mean packed-dirt. If it's not packed, it's useless. It's a matter of atoms with heavy nuclei.
When I say effective, I mean overall. A product of cost/shielding.
That's why water is more effective overall. It's much easier to produce 7 inches of water than 3 inches of packed-dirt to halve radiation.
If cost and availability wouldn't be a problem, then you can obviously use depleted uranium, lead or concrete, which are much better at stopping gamma radiation, but much more expensive to obtain. Sometimes you don't have an option. For example nuclear reactors normally shield their fuel using a mixture of concrete and water-cooled lead.
That said, used nuclear reactor fuel is actually kept in water pools, not packed-dirt sheds.