I understand that the 'Digger' term didn't come into widespread use until 1916, possibly 1917, in France.
However, (I think it was) Birdwood is attributed with the comment, (within a day or two (possibly within a few hours) of the Gallipoli landings, when it had become quite obvious that a quick advance to the opposite coast was no longer an option), that the Australians should "dig, dig" [forget the whole comment] to maintain their very tenuous hold on the ANZAC beach head.
It might not be too widely known, but the Australians, using the civilian expertise of many of their soldiers, also conducted very extensive tunnelling operations at Gallipoli. Some of those tunnels, many still in very good condition, have only been uncovered over the last few years.