An Experimental Investigation of Shock Shields.

A series of tests was conducted to obtain information concerning the effectiveness of a shock shield of reinforced concrete between the ground surface and a buried structure as a means of reducing the shock transmitted to the structure due to airblast loading. Two shock shields were used. The diameter of the shields was 20 inches and the thicknesses were 6 inches and 2 feet. The structure was 20 inches in diameter with a thickness of 5 feet. Tests were performed in a 2- by 40-foot shock tube without shock shield and structure soil only, with soil and structure only, and with different thicknesses of shock shields at various depths above the structure but not in contact with it. The shields and the structure were buried in 20-30 Ottawa sand and subjected to a dynamic pulse with a maximum pressure level of approximately 500 psi and a positive-phase duration of 20 msec. Surface-flush air pressure gages were mounted in the walls of the shock tube. The shock shields and the structure were instrumented at the top with stress gages, accelerometers, and velocity gages. Stress gages were also mounted in the bottom of the shock shields. Stress gages and accelerometers were placed at various depths in the sand above the structure. Comparison of experimental results with theory was done by use of a plane, one-dimensional, finite-difference analog of the basic conservation laws of continuum mechanics mass, mass, momentum, and energy. Author