F
An Explanation of the Efficacy of Simultaneous Detonation for Explosive Channel Excavation
Simultaneous detonation of space-buried explosives can produce a buried line-charge analog, in the surf zone and up the beach, forming a channel from which most mines and obstacles are removed in a very short time. Some of the mines may be destroyed, but the purpose of explosive excavation is mine removal—the state of the removed mines is not necessarily relevant. The bottom of the channel is deepened, and mines and obstacles that may not be removed will be on or in the new bottom, which should be deep enough that assault vehicles will not contact them. Contact is important because contact mines are generally the most difficult mines to destroy. After the excavation stage by the line-charge analog, water will flow back into and up the length of the channel. Characteristically, the line-charge analog has a small lip at the end, and much larger lips on the sides. The water flow up the channel will smooth its contour and further reduce the end lip.
It has been suggested that linear sequential detonation might be obtained by dropping, in one pass, a line of spaced penetrating bombs that have fuses with sequential delays. Sympathetic detonation could cause a nearly simultaneous detonation of the line, but this may not be reliable unless arranged for beforehand by special fusing. If a second bomb is in the crater radius formed by the first of the sequence, it will be moved from its original position—this was established before the first crater was formed—and may be damaged by the first bomb's explosion shock-wave. If the second bomb is outside the crater of the first bomb, its explosion can throw some of the mines and obstacles back into the first crater.
Random timing of explosions of a line (or any other arrangement) of bombs will also cause mines and obstacles to be thrown back and forth among the
craters, and the resulting channel would be partially filled with debris-possibly including still-active mines. The bottom and sides of the channel in these cases would be irregular.
Sequenced explosions also lack the dynamic synergism of simultaneous detonation that creates a channel of relatively uniform width with a small end lip. Water flow, in the sequenced case, will occur after each explosion to smooth crater edges, but the final explosion at the end will not benefit from the previous ones to reduce its lip. It is unlikely that sequential explosions would create as deep a channel as simultaneous detonation of the same amount of explosive material.
A slow sequenced-explosion experiment has, in fact, been done at the Navy's Panama City Laboratory Test Site, in which a first explosion on the bottom (at water depth of about 5 feet) pushed aside mines and obstacles, and after things had settled a second explosion, closer to the edge of the moved mine-obstacles pattern, was set off to push them out some more. It should be possible to continue this pattern to form a cleared channel; this could be continued into shallow water and up the beach, by exploding sequentially so that ejecta are always thrown away from the craters previously formed, but, as noted, this is a slow process.
The excavation accomplished by simultaneous detonation results mainly from the explosives' gas bubble; the bubble growth time, of the order of several hundredths of a second, sets the bounds on the degree of simultaneity required. A 1992 study on mine countermeasures conducted by the Naval Studies Board1 suggested that simultaneity to within ≤ 0.01 seconds is required.
All this assumes that the measure of effectiveness for channel clearance is mine removal. If mine destruction were the measure, simultaneous detonation would offer the advantage only of smoother final channel shape, and a small end lip. Among the impediments to breaching the surf and craft landing zones are the durability of some of the mine types that are typically deployed in near-shore waters and the consequent difficulty of destroying them.
