Is sand fluids

No, sand is not a fluid. It is a finely divided solid. Generally speaking, fluids are liquid, gas or plasma (with a few other possibilities), and shear stress will continuously doform these substances. An example might help, so let's suggest one.

You can push your hand down to the bottom of a bucket full of water, but you can't push your hand down to the bottom of a bucket full of sand. The water in the bucket deforms continuously as you push down, and you won't have the same result pushing your hand down into a bucket of sand.