Hi Canny lass, Pit Props are/ were usually called timbers, and it was usually the young rookies job hauling and setting the timbers, placing them in areas needing support, quite the job for a young 15 year old, thats were they learned mining and miners! nothing like hard work for the old timers teaching the youngsters to be be humble.
HPW would know a lot more about the wooden timbers, today (at least over here) I think they mainly use steel arches and hydraulic rams etc but wood has a bit more "give" in it.
1.a simple brake on a vehicle, especially a stout stick or bar inserted between the spokes of a wheel to check its motion.
I had heard the expression spagging the wheels but just thought it meant using a piece of the timber to wedge the coal tub wheel, but it was a bit more than that, this would explain the "wheels and inclines."