Book Description

The effectiveness of frangible backfill (glass bottles) in protecting underground structures from the violent motions produced by nearby explosions was investigated. Two test structures and one comparison structure were used. Each test structure was a reinforced concrete pipe enclosing a steel cylinder separated from the pipe by rubber O-rings, with glass bottles placed around the sides and bottom of the pipe. The comparison structure was a concrete pipe with solid concrete bottom. All three structures were buried with their axes vertical, and their tops approximately 2 feet below ground level. A concrete slab 1 ft thick was set above each, flush with the ground surface. One test structure and the comparison structure were 750 feet from ground zero (229-psi peak verpressure). The remaining test structure was 1,050 feet from ground zero (104-psi peak overpressure). The peak accelerations of these structures, produced by shear forces exerted against their sides, were reduced by the frangible backfill to 26% or less of those that structures in intimate contact with the soil would have experienced. Four years after the shot the structures were excavated. All the bottles around the sides of the test structure at 229 psi were completely crushed; only a fourth of the bottles at the 104 psi were broken, most of these on the upper half of the structure.