Deep water excavation with shaped charges: a case history in Lake Mead, Boulder City, Nevada, USA

摘要

Lake Mead, the largest man-made reservoir in the United States, is located about 30 miles southeast of Las Vegas,Nevada. For the construction of Lake Mead third water intake, which is entirely placed underground, an underwaterexcavation was needed at a depth of 100 m (330 ft): a large surface had to be deepened by 20 m (66 ft) in basalt.New technology that would fit the special circumstances of this job was not available, so the old one, the “brutal”,not-precise but effective technology of the shaped-demolition-charges was chosen.It was then found that no shaped charge existed that fit the underwater specifications of this job so a new one hadto be conceived, as well as its deployment system and technique, monitoring and survey procedures. For this aninternational task of experts was put together.Basaltic stone is strong and resilient. It has a high resistance to metallic jet penetration, close to that of ceramicwhich is therefore used in the defense industry on steel tank armor, to add extra protection to the penetration ofthe grenade's jet. High energy of the jet produced by the detonation of the charge was required for basaltic stoneand, for this, an adequate liner material, the best quality of execution, right form and mass as well as an adequatestand-off in air were needed. To keep the charge stand-off water free at that depth, a specially fitted shell had tobe coupled to the charge, ballasted to prevent floating. This was one of the “rings” of a chain of “problems tosolved” both in the design phase and also with work in progress, targeting to optimization of the production technology,of the product itself and of the method of use.Since large quantities were needed, a solution targeted to minimize environmental impact was adopted. Biodegradablematerials were chosen to reduce from one hundred years to five, the bio-degradation time of the plasticresidual from the charge canister.This paper describes the development process, application, and results.