VFX physics / granular style

I’m wanting to create a sequence of a truck dropping dirt from its tray,
I’m just not entirely sure how to initially approach a concept like this, I essentially need a tray to fill up with dirt and for it to semi-realistically drop from the tray when it has been lifted.
I guess I’m asking if there are any good resources for myself to look into that could help create a concept like this in UE4.