This past spring, between 69th Street and 72nd Street on Second Avenue, cages descended every eight hours, five days a week, lowering roughly 50 men in neon vests and hard hats into a deep hole. Overhead, fluorescent bulbs provided a noonish light and yellow ventilation tubes undulated. A cool, roaring wind filled the void and carried the intense aroma of Emulex explosives, an ammonialike, Fourth of July smell. Men with tripods surveyed; men with blowtorches welded; men guiding hoses poured concrete (men outnumber women 100 to 1). They took brief lunch breaks and relieved themselves hastily where and when they could.