Re; Raises
When I was working at the Mosaboni copper mine, in Bihar,
India, in 1958-60, the vertical interval between successive levels
was 120 feet.  Mostly the raises put up in the vein were inclined
at about 40 degrees, but a series of ore transfer raises we put
in were inclined at 60 degrees.
As in the case of other raises which have been described, 
access up the raise was by steel rope ladder, set to one side.
The "working platform" from which the round was drilled 
consisted of two planks of wood supported on two short
drill steels inserted in holes drilled into the footwall.
Barring down of loose rock, and construction of the stage
was done by "timbermen" on the morning shift. When I was 
on morning shift and on my second round of the section of
 which I was shift boss, my job would include marking up
 the round to be drilled in the afternoon shift.
When I was on afternoon shift, I would inspect the round
which had been drilled, and agree with the drillers if they
needed to put in an extra hole -- sometimes they could not
drill exactly to the pattern required. The raise drillers were
all Gurkhas, drilling with hand-held Holman drills, without
benefit of air-legs. The drilling machines were pushed up 
by shear strength.
All blasting was done on the night-shift by Indian blasters
under the supervision of an Indian foreman, using safety 
fuse of (hopefully!) adequate length to allow the blaster 
time to climb down.
One of the English staff at the mine, a mine-captain engaged
as a "master driller", told me that his previous job had been
to operate a one-man fluorspar mine in Derbyshire. He liked
living dangersously, and told me with pride of how he had put 
up vertical raises without ladders -- he just had an array of old
drill steels stuck in holes in the side walls, and scrambled down
these quickly after lighting the fuses!
The latest way to make a raise, of course, is to use a raise-boring
machine. This sits in the upper level, and first drills a hole of about
eight to twelve inches diameter down to the lower level. Once this 
has been done, a reaming head is fitted to the drill string at the lower
level, and the machine then reams to hole out from the bottom
upwards, up to about eight feet in diameter at a single pass.
The commonest make of raise-boring machine is Robbins, and
in Mexico, where all raises are now made in this way, the modern
name for a raise is "Un Robbins". At one mine I visited in 1986, 
an underground vertical shaft consisted of two parallel Robbins-
bored raises, with one cage in each.
The latest development of the Kiruna iron ore mine in Sweden,
which involved the construction of several major deep-level
ore-passes was also carried out using Robbins raise-borers, 
the diameters of the initial raises being slashed out by drilling 
radially outwards from a suspended stage within the raise.
Tony Brewis
stage

the lower level
his previous


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%