BLASTING AND BURNING TREE ROOTS
[Illustration: BLASTING AND BURNING TREE ROOTS]
Blasting by gunpowder or dynamite is not only the most expeditious
but also the cheapest method of clearing away tree stumps and large
logs. In preparing to blast a stump, great care must be exercised to
bore the hole in the right place and not to use too much explosive.
For blasting powder the hole should be 1½ in. in diameter, and should
penetrate to the centre of the stump. It must not be too low down, lest
the bottom should blow out and the force be expended in shattering the
ground instead of the stump or log. In selecting the spot to bore for
the powder, choose the hardest part of the root and ensure an equal
thickness of wood all round, and even splitting of the log will be the
result. The following is a good way of putting in the powder:—For large
stumps of from 2 ft. to 4 ft. in diameter about 3½ in. depth of coarse
blasting powder should be inserted in a hole 1½ in. in diameter. The
end of the fuse should be put into the centre of the powder, and left
protruding for 15 in. outside the hole, which is filled with dry sand,
consolidated, or packed around the fuse by means of a coarse iron wire.
The outside end of the fuse should be teased out and lighted with a
match, and as it will require over a minute for the fire to reach the
powder, time is given for the operator to find a place of safety.
=Burning Tree Stumps.=—With a 2-in. auger bore a vertical hole in the
centre of the stump from the top towards the bottom. In the side of the
stump, near ground level, bore a horizontal hole towards the centre,
so as to open into the vertical hole, drop some fire down the vertical
hole, and if the wood is at all dry the draught of air entering by
the horizontal hole will, like the draught of a chimney, maintain the
combustion of the fire in the centre, until this slowly spreads and
ultimately burns away the stump.
Another and equally simple method of destroying stumps of trees is as
follows:—In autumn bore a hole 2 in. in diameter and 18 in. deep, put
in 1½ oz. of saltpetre, fill with water, and plug up close. In the
following spring put in the same hole half a gill of kerosene oil and
then light. The stump will smoulder away without blazing, down to every
part of the roots.
=American Method of Blasting.=—At Studley Horticultural College,
Warwickshire, the American method of blasting was successfully carried
out and reported upon by Mr. A. P. Long as follows:—
A hole is bored with a long auger or crowbar in a sloping direction
from one side of the stump to its base, generally from 2½ ft. to 3½ ft.
deep. The bore-hole is cleaned out, and a number of dynamite cartridges
inserted, each being firmly pressed home by a wooden rod. A primer
cartridge containing a detonator is then placed on the top of these,
and the bore-hole is filled with clay and tightly rammed. The primer
is either connected directly with a safety fuse, or to a high-tension
battery, by a cable, and is afterwards fired. As dynamite strikes
downwards as well as upwards, the effect of the explosion is that the
roots and stump are all either ejected or loosened, so that they can be
easily removed by hand.
The American method is less costly and more speedy than the methods
hitherto used in England in removing stumps. If there is no man on
the estate qualified to handle explosives, an expert must be employed
at about £1 per day, besides travelling and hotel expenses. Three
men—an expert and two labourers—can bore holes and blast thirty sound
stumps per day easily. If the stumps are hollow in the centre, two or
three bore holes are necessary for each stump, and in that case twenty
only can be blasted during the day. Taking the pre-war wages of two
labourers at 2_s._ 6_d._ each per day, the cost of boring and firing
averages 2½_d._ per stump, exclusive of the expert’s fee. The expert’s
fee increases the cost by about 2_s._ per stump.
The explosive used is Nobel’s dynamite, in the form of cartridges,
costing 9½_d._ per lb. The average quantity used for each stump is
between 2 lbs. and 3 lbs. (about twenty to thirty cartridges), so that
the cost of the explosive is not more than 2_s._ 6_d._ per stump. The
detonators and fuses required only cost a few pence. Summing up, the
cost per stump is:—
_s._ _d._
Expert’s fee 2 0
Cost of boring 0 2½
Cost of explosive 2 6
Detonators and fuse 0 9½
———————
5 6
Misfires and partial removal of stump may require fresh borings and
further charges of explosive, thus increasing the cost. By employing a
skilled estate hand capable of using explosives instead of an expert,
the expense, however, is greatly diminished.
By the old method of grubbing and jacking, stumps were removed at
Studley some time ago at the high cost of about £2 5_s._ each butt,
and even then success was only partial. In another case, on an estate
in Norfolk, where an old pasture was converted into a plantation of
mixed trees, trenching at the cost of £18 per acre had to be resorted
to on account of the presence of roots and stumps of old trees. In
this case it would have been much cheaper to have removed the stumps
by blasting. The demonstrations at Studley showed that both sound and
unsound stumps could be successfully blasted, and whole trees—an Apple
and an Oak—were also uprooted by the same method with equal success,
using only one bore-hole and about the same charge of explosive. The
timber of the trees so treated, however, is very much split, so that
blasting is only advisable when the timber is considered of little
value.
The particular explosives used are unaffected by damp, and, in
consequence, the method is applicable in both wet and dry situations.
Firing the charges was done at the demonstrations mostly by ladies, and
a photographer was able to get sufficiently near to obtain photographs
of the effect of the explosion without danger. The principal
recommendations of this method, therefore, are cheapness, effectiveness
and safety.