Rock Blasting / A Practical Treatise on the Means Employed in Blasting Rocks for Industrial Purposes

by George G. André

The first charge produced but little effect; a second failed from the case not being water-tight; a third charge was more effective, as it lifted the tree and the boat partially out of the water. The positions of these gun-cotton charges are indicated by circles on the [figure]. The next day, two charges of gunpowder, of about 70 lb. each, were placed under the boat, these charges being lashed on to the snag by the divers. These charges consisted simply of common oil-tins, carefully cleaned and painted over with red-lead paint. The bunghole was closed by a wooden plug, bored through to allow the fuse wires to pass. This plug, after being inserted, was coated over with a waterproofing compound. The effect of the two charges was to completely demolish the boat. Another charge of 50 lb. removed the tree underneath. The positions of these gunpowder charges are indicated by squares in [Fig. 51].

The next obstruction met with was a sand bank caused by a boat which had broken in half and then sunk. The sand nearly covered the boat, so that there was little else to operate upon. A charge of 80 lb. (one large charge being considered preferable to two or three small ones in getting rid of the sand), placed close to the part of the boat that was visible, made a considerable crater, and a second charge of 80 lb. was placed in a much more favourable position, as nearly all the boat was removed except portions of the bow and stern, which required two separate charges of 50 lb. each before they disappeared. In half an hour, the whole of the sand bank had been washed away by the stream, and there was from 3 to 4 feet of water over the spot where before the sand was high and dry out of the water. The removal of this obstruction was dangerous, owing to the nearness of the boat to the surface, the consequent small resistance offered to the projection of its pieces through the air, and the largeness of the charges used. Had, however, small charges been used, it is more than probable that the small craters made by them would have become too quickly filled up again to have been of any good in facilitating the placing in position of subsequent ones.

The following day, a large mango tree, about 4 feet 6 inches in diameter, was destroyed by two 50-lb. charges, which broke it up into three pieces, easily removable ashore.

A few days later, a large trunk of a tree, about 3 feet in diameter, was removed with two 50-lb. charges; but the depth of water over it was so small that a large portion of the trunk was thrown a considerable distance on shore. The next day a large tree which had formed a sand bank was very successfully removed by a charge of 50 lb. placed among the roots, it being considered that a smaller charge than 50 lb. would not have effected the purpose. Opposite to Kásimpore, a boat was removed with a charge of 50 lb. placed in the centre up-stream, which entirely demolished it, the pieces being all dragged ashore. At Mootyá, a large cotton tree, the wood of which is extremely tough, was found with many large branches projecting out of the water. A charge of 70 lb. tied under the tree at the springing of the branches effectually broke it up, and the pieces were all hauled to land. Three miles farther down the river, an attempt was made to destroy another large cotton tree with a similar charge, but it only broke it into three pieces, and two more charges of 50 lb. each were necessary to clear it away effectually. This tree was, if anything, slightly larger than the last, i. e. from 3 to 4 feet in diameter, and there was less water over it.

Farther on, the party came across a collection of three or four trees, with their branches interlaced, lying on a sand bank near Alumpore Dáldah; these were sufficiently broken up by a 70-lb. charge to make them easy of removal by coolie labour. Opposite to the village, another awkward snag, in the shape of a large tree sticking up in 30 feet of water, was destroyed by tying a 70-lb. charge at its base. A charge of 50 lb. of powder under this head of water, or even a smaller amount, might have been sufficient, but as the work had to be done quickly, not much account was taken of a few pounds of powder more or less, provided the object was attained. At Gomashtapore, a large tree, branches and all, was found in 25 feet of water, lying in the channel under the bank. The current here was considerable, and some difficulty was experienced in placing the charges. One charge of 70 lb. broke the tree in half; another of 50 lb. at the springing of the branches broke them up; and another of the same weight got rid of the roots. Below Gomashtapore, a large mango tree was demolished with 60 lb. of powder. A short distance farther on, a bad bamboo snag was met with. These bamboo snags, which were merely the roots of the bamboos with perhaps a dozen or so whole ones left, gave much trouble. [Fig. 53] gives an idea of what these snags are like. It was found impossible to place a charge underneath this one, so an opening was prized between the bamboos, and a charge of 70 lb. rammed down pretty well into the middle. This cleared the whole of it away and opened the channel.

Fig. 53.

At Chandpore, at a re-entering angle of the river and in a place peculiarly dangerous to navigation during the rains, was an enormous banyan tree (Ficus Indica), the main trunk of which, to judge from the branches, must have been at least from 12 to 15 feet in diameter. An approximate measurement was made with a pole, but any such measurement can only have been a very rough one.

Fig. 54.