Some Case Histories of Armor Stone Production

by Mel Hill,

Abstract: The blasting techniques used to produce armor stone, derrick stone, and underlayer stone [one to twenty tons] for the construction of rubblemound breakwalls and the confined Dike Disposal areas [for polluted dredgings from rivers and harbors] along the Great Lakes is vital to the prolonged durability of those specific stones and structures. Quarry faces and blasting patterns that have been used for the production of aggregates cannot be used for the production of armor stone. Blasting patterns in which burden and spacing were common terms are now used in the sense that line drilling or presplitting predominate the scene, and are far more productive than providing over sized, fractured material for the use of armor stone for the marine structures. It becomes obvious that small diameter holes, low benches, and slow velocity powders produce armor stones that usually are fracture free. Seasonal blasting is a major problem for most quarries producing armor stone. Warm days and cool nights play havoc on a blasted product. Blasting for armor stone must be limited. Products blasted in the fall, winter and early spring should not be accepted unless they have been stockpiled for at least two years. In the first century B.C., Vitruvius wrote The Ten Books on Architecture and stated: ...necessity drives us to use their products, we must proceed as follows, if we wish our work to be finished without flaws. Let the stone be taken from the quarry two years before building is to begin, and not in the winter but in the summer. Then let it lie exposed in an open place. Such stone as has been damaged by the two years of exposure should be used in the foundations. The rest, which remains unhurt, has passed the test of nature and will endure in those parts of the building which are above ground. This precaution should be observed, not only with dimension stone, but also with the rubble which is to be used in the walls.

Subject Headings: Rocks | Armor units | Case studies | Blasting effects | Construction methods | Levees and dikes | Cracking | Winter | Riprap | Great Lakes

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