Battalions composed of peacetime miners and holders of related jobs would often be attached to Royal Engineers Companies mostly as labour though their skills as excavators were appreciated. They were often regarded as being outside many military norms and disciplinary regulations -- they weren't expected to present a 'smart' appearance for the most part but could also be looked down upon by the hierarchy. AFAICT, strangely there was no effort to train them up as combat engineers.

At the same time, the business of mining was understood to be highly skilled. On many occasions, the German troops could be clearly heard without any assistance from the head of a tunnel yet they'd eat through the soil rapidly and in total silence. It was regarded as highly dangerous as discovery would doom many workers.

There's a sad story in Forgotten Voices of the Great War about two slouching along head-down along a trench, supposedly their usual way of walking. A sergeant on duty shouted 'Halt!', went unnoticed by the men, shouted 'Halt!' again and then fired, by chance killing both instantly with a single round. It would have been inconceivable to the sergeant that two soldiers would twice ignore a command to halt in a front line trench, and he was unfamiliar with the miners' habits.

Sources:

Max Arthur, Forgotten Voices of the Great War

Peter Simkins, Kitchener's Army: The Raising of the New Armies 1914-16