As a high generalized rule of thumb, British trenches were the deepest in the are, 6-8 feet deep, with duckboards to walk upon, and a firing step on the No Man's lnad side.
They also had extemsive "bombproofs"--dugaout underground quarters for sleeping, eating, medical care, etc.
Now, that's for trenches on the Main Line of Resistance. Combat trenches pushed forward to the edges of NML were less organized.
NML would be laced with various slit, recce, expolration trenches; some only 2 or 3 feet deep, and overrun in two directions and pounded by artillery fires.
