when you got a lot to dig, and a lot of people that have a shovel and can DIG. all you need to do is be the boss, so place several dig orders, then use K and build up the trench. like this.
imagine that those sandbags are actually dig orders. and you can send soldiers build it anytime you need. by pressing the right mouse button when you have the shovel in your hands like you do whit the hammer in engineers squad.
once the dig orders are set, just use K and assign soldiers whit shovel to dig.
it will be interesting has well, shovel equip soldiers able to build things at 1/4 times the speed. but that’s only a opinion.
cheers.