DRAINAGE WITH EXPLOSIVES.

Taranaki Daily News, 8 May 1919, Page 7

DRAINAGE WITH EXPLOSIVES.

MAKING SWAMPS PRODUCE. Many parts of Great Britain and Ireland are entirely unproductive owing to their swampy and boggy condition. The present time (writes "Tunneller" in the London Daily Express) seems to be one in which the reclamation of these areas should he carefully considered. It is a perfectly simple matter, and merely consists of proper drainage schemes "being put forward to make these lands as fertile and rich as those alluvial soils of the Nile, where Egypt's plenteous crops are raised. Ditching the land by moans of dynamite is a speedy and labor-saving method of draining the swamps, and because of this it is also essentially a very cheap one. There are many thousands of acres of land that cannot be tilled owing to a river or stream following a circuitous route, which, by means of explosives, could be readily straightened, and these areas reclaimed for cultivation.

There are two methods employed in blasting a ditfh, tlie one for dry soil and the other for wet earth. In the former case, holes are put in between two and three feet apart, and are connected up to the exploder, or battery, and all fired simultaneously, while in the latter case the holes are placed nearer together and contain larger charges, being fired by a fuse ignited in the centre charge, this being sufficient to ignite the charges on either side, and so continue the blast along all the length prepared. Holes in dry land require well tamping, but those in swamps and under water fill with mud and water, and do not require further tamping to make the explosive do its work.

Of course, ditches may be made any width, by adding one "or more extra rows of holes, and the grading of the ditch thus made can quite readily be accomplished by altering the depth of the holes.very_slightly in the direction in.winch the dip is required. An inch in a hundred feet is sufficient fall. The depth of the hole should be about six inches less than the required d?pth of the ditch, and it may be said that deep ditches will give infinitely better results than shallow ones.

Swamps are usually to ho found on the lowest ground, and exist because the water is held by a hard, impervious stratum below the top soil, and it is necessary that this hard layer or stratum should be penetrated and fractured by the explosive, so that drainage 'may be effected. If this "hard-pan" or impervious stratum lies directly upon the rock, the hole should be bored through it, so that the explosive will lie upon the rock and tend to fracture and cause fissures in it, but usually beneath it will be found a pervious soil, which will quickly drain the swamp. As regards cost, ditching with explosives only comes to about half the cost of ditching with pick and shovel. Approximately, drainage by means of explosives costs from fid to 9d per cubic yard, while the old-fashioned pick and •hovel method works out at from Is to

!• "'l. The amount of explosive to be used per hole naturally depends upon the naiur." of the ground and the depth of the nolo ar.d the. amount of woik each shot has to do, while the number of holes depends upojii the size of the swamp, the depth of the impervious soil, and the amount of water to be lowered. A_ four-onm-e ..artridge of dynamite per 15 inche= of depth is an approximate rule, which will be found to give good resultß.