Grenades are not specifically designed to kill, the purpose of them is to 'stun' the enemy for a few seconds while the killing party finishes them off with automatic fire.
Here's how we cleared Iraqi trenches in Gulf war 1 using a two man fire team.
First guy looks round corner of trench (they were made in a zig-zag way) posts grenade then takes cover behind second guy. When the grenade explodes the second guy moves into trench firing his weapon (30 rounds) into anything soft/ or that moves, he then moves to the next corner of the trench, looks round corner of trench, posts grenade etc etc, they carry on until they reach their objective.