井筒沈下工法による立坑開さく時の水中爆破に関する2, 3の基礎的研究
1969 年 85 巻 972 号 p. 237-243
詳細
1969 年 85 巻 972 号 p. 237-243
When a shaft is sunk by the well sinking method with air blowing, the edge point of the well sometimes meets a hard sedimented soil or a weathered tertiary rock. In these cases the power of detonating explosive is usually utilized to break such a soil or a rock under the cutting edge of the well.But the procedures employed in these blastings are mostly based on experience only and we know some wells sunk in the past had been broken by a blast due to the unsuitable amount of charge of explosives.
Now, the authors have carried out some fundamental investigations on the phenomena related to the underwater explosion in a shaft with the object of obtaining the useful data for the design of blasting operations to sink the shaft well more effectively and safely.
The main results obtained are as follows:
1) In the range of depth, about 200m from the water surface, the pressure pulse always propagates in water with the velocity of 1, 500m a second.The peak pressure decays with the exponent of 1.76 against the distance and it has nothing to do with the kind of explosives used.
2) Shinkiri dynamite, a gelatine dynamite, when sealed tightly in the pressure-proof vinyl tube, can be detonated in water with 200m from the water surface.
3) When we indicate the index of power of underwater explosion exhibited by Shinkiri dynamite as 100, the corresponding indices for Shoan dynamite, an ammonium nitrate dynamite, and the black powder can be represented as 62 and 48 respectively.
4) If we perform an underwater blasting at the depth of 200m, nearly twice much explosive is necessary to get the full crater compared with the amount needed near the water surface.
