CHAPTER XXXI

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.