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

by George G. André

Fig. 55.

The trunk was lying in deep water, but the branches, more like an accumulation of large trees, were lying stretched out for a considerable distance over the bank, covering an area of more than 80 square feet. A charge of 200 lb. of powder was made up in an indiarubber bag, and placed by the divers in about 28 feet of water, well under the trunk of the tree. The effect of this was to split the trunk up into several pieces, each of which subsequently required separate removal. A 70-lb. charge was next fired under two of the largest pieces in 18 feet of water, and this broke them up completely. Having now run out of all the cases for powder, three charges of gun-cotton, similar to the first, were made up, and fired separately, each placed under a good thick branch, about 8 feet in girth. The effect of all three was prodigious; seemingly greater than that of the 70 lb. of gunpowder. As there were no more cases left, and time was precious, some common earthenware ghurrahs were obtained from the village as a makeshift. These held about 20 lb. of powder; the fuse was placed in the centre in a disc of gun-cotton, and the neck was closed up with damp earth, white-lead paint, &c., just in the same way as the gun-cotton charges had been. A rope for lashing them to the obstacle was securely fastened round the neck, and the fuse wires were tied under, this lashing, leaving a small loop towards the fuse free, so as to avoid any chance of a strain being brought on the fuse in lowering the charge. [Figs. 54] and [55] show the arrangement of this charge. The first one tried had but little effect when placed under a branch of the tree in deep water, and it was accordingly determined to wait for cases from Calcutta; but after waiting five days without their appearing, three more of these charges were tried, and this time with very excellent results. They were indeed so satisfactory, that the same evening four more were made up and fired. The first under a mango tree a little farther down the river. This broke it in half, throwing one part high and dry on shore, and the other into deep water. The other three were fired under the remaining branches of the banyan tree with very good effect, cutting them away.

It is more than probable, observes Lieut. Green, that the good results obtained with all these ghurrah charges were entirely due to the gun-cotton disc inside causing the gunpowder itself to detonate, so that the thinness of the envelope was of little moment in determining the force of the explosion.

The tin cases having arrived, the rest of the powder was made up into five charges of 48 lb. and three ghurrah charges of 20 lb each. About four miles farther down the river, there was an old peepul tree lying in mid-channel, with several of the branches above water. Two tins, one placed under the springing of the branches and the other under the roots, blew away the lower branches on which the tree was resting, and it sank slightly in the water. A ghurrah was next fired under the trunk with splendid results, the tree disappearing entirely except one branch, which required another small charge to remove it. The trunk of this tree was nearly 8 feet in diameter, but of soft stringy wood.

On returning to camp, a small charge of 2 lb. of gun-cotton was made up in a section of bamboo, and used against the banyan tree with very good effect, and a ghurrah charge demolished the last branch but one. The next day 1¹⁄₂ lb. of gun-cotton in a piece of bamboo finished the last of this enormous tree.

After clearing away several more trees, the foundations of an old factory, which had slipped into the stream, were removed by introducing two charges of 1¹⁄₂ lb. of gun-cotton, in the ends of two bamboos, well into the crevices of the masonry under the water.

Another obstruction consisted of a row of old piles, about 15 inches square, stretching across the river below the surface of the water. Six of the most dangerous of these were removed from the dry season channel with ghurrah charges tied to the foot of the piles.

An old well that had fallen bodily into the water was afterwards met with. The position of this well is shown in [Fig. 56]. A charge of 4 lb. of gun-cotton completely destroyed it.

Near Azimgunge, the trunk of a very large peepul tree was found sunk in deep water. It was so large that it was thought necessary to place a 100-lb. charge underneath it; this charge broke it up completely, but two small charges of 20 lb. each were subsequently required to remove the pieces.