IMPROVE- MENTS IN SINKING, QUARRYING, AND EXCAVATING IN THE EARTH
Year: 1863

page_text: PROVISIONAL SPECIFICATION left by James Mitchell at the Office of
the Commissioners of Patents, with his Petition, on the 22nd October
1863.
I, JAMES MITCHELL, of Dyke Head, in the County of Lanark, North Britain,
Gentleman, do hereby declare the nature of the said Invention of "IMPROVE-
MENTS IN SINKING, QUARRYING, AND EXCAVATING IN THE EARTH," to be as follows;
that is to say-
This Invention, as applied to sinking pits, will come into operation where;
by the ordinary process, the surface and softer materials have been passed
through and the rock or other hard strata have been reached. It is applicable
to any form of pit or well, and to deep quarrying and excavations of all kinds
where blasting is employed. After reaching the rock, the next operation will
be to sink with the common boring rods or other means one or more bores, as
may be best suited for the purposes of sinking or excavating, according to the
"lie of the strata," and for giving the force of the blasting powder the greatest
effect on the mass to be blasted. In no case, almost, in sinking an ordinary
rectangular pit or well, will a greater number of bores be required than six,
four near the corners of the rectangular space or mass to be acted upon, and
two near the centre line of the rectangle, each about a third or fourth of its
whole length from each end, and very seldom so many, as in most cases one,
two, or three bores will be sufficient. These bores, which are from two to
three inches in diameter, are put down or sunk to the depth proposed to be
reached either at first or in successive stages, as the quantity of water, the

page_text: "
depth of the pit or well, and other circumstances may require, and will ulti-
mately reach the coal or other material to be mined or wrought. Care must
also be taken in this operation to note the exact place of each firm and solid
stratum or layer of rock that may be passed through. As each of these bores
is completed to the depth decided upon and cleaned out it is to be filled up with
round pieces of malleable iron or "plugs," tapered at each end, of various
lengths and of such thickness as to decend easily in the bore; but also at the
thickest part, which is near the top, to be of such a diameter as nearly to fill
up the area of the bore. These pieces or "plugs" of iron or other hard metal
are of such lengths as to afford, when taken out in the process of sinking,
sufficient depths for the blasting of the rock or other material to be excavated.
In working strata of a comparatively soft nature these plugs will be long, and
in hard rock short, but in all cases the tops of some of them will be so adjusted
as to be placed opposite such hard rock or strata as occurs in the pit, and so
as when covered with "caps of lead, hereafter described, will effectually
intercept and prevent the water from rising in the bore, and thus leave the pit
or other excavation at all points of its depth reached in the sinking as free
from water as under the present processes of sinking. These pieces of iron or
plugs, which are tapered at both ends to a blunt point, have a small lateral
hole or holes, or notchs or other catchs, formed in them near the top to aid
in their extraction when reached in succession. The lower portion of the
plugs have a slight taper gradually downwards from the part which nearly fills
the bore to allow of their being pulled out more easily. As each of these
plugs is inserted in the bore and resting on one another, a "cap" or short
cylindrical plug of lead, zinc, or other ductile metal or composition nearly
fitting the diameter of the bore, and with a recess in each end of it to fit the
blunt tapered ends of the plugs, will be passed down and rammed close, şo that
the upper and lower ends of the cap being expanded over the ends of the
plugs will be so firmly wedged all round as to prevent the under water from
rising to impede the operations, and also to afford the necessary resistance to
the blasting process going on above till its own place or depth is reached. In
the sinking, pieces of dry wood, cement, gutta percha, or other material may
also in some cases be substituted for the lead "cap" in passing through the
several strata.
The bores which it has been judged proper to adopt having all been carried
down to the requisite depth and afterwards "plugged" up as above described,
the proper operations for sinking will commence. The first plugs, say, for
instance, those nearest the centre of the pit or well, being withdrawn, the
blasting powder will be inserted, and the space above being "stemmed" or

page_text: "tamped" sufficiently, the charge will be fired off in the customary way, or,
preferably, in the case of a pit, by galvanic apparatus from the bank.
In many cases, also, in place of the usual mode of "stemming" or
tamping," iron plugs are used similar to those above described, first inserting
next the powder a small piece of iron, nearly filling the diameter of the bore
with its top, in the shape of a comb, then passing down one of the "
"of
caps
lead or other metal or composition, as before described, and then an iron plug
of the description before referred to and of suitable length. In this way a
speedier and more effectual mode of "stemming" or "tamping" is obtained
than in the modes at present adopted, especially when the upper "plug" is
weighted or kept down by angular rods to the sides of the pit.
The produce of these blastings, and all debris and broken-up materials occa-
sioned thereby, being removed and other necessary operations forwarded, the
same process as above described will be repeated with the other bores, under
such variation as the condition of the bottom of the pit, the position of the
pumps, or other circumstances present may require. In all cases, where prac-
ticable, two or more of these bores will be fired off simultaneously, and in
many instances one or two of those nearest the "dip" of the strata through
which the pit is being sunk will be sufficient to facilitate advantageously the
placing of the pumps and other operations in breaking-up the strata. In
many cases, also, after the iron plugs before described are withdrawn, the
well-known mode of "plug and feather working" can be most advantageously
employed in place of that of blasting for smoothing the sides of the pit.