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Blasting Vibrations and Their Effects on Structures.

Nicholls HR; Johnson CF; Duvall WI

NTIS: PB 231 971 :105 pages

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10008822

This report presents the results of the Bureau of Mines 10-year program to study the problem of air blast and ground vibrations generated by blasting. The program included an extensive field study of ground vibrations; a consideration of air blast effects; an evaluation of instrumentation to measure vibrations; establishment of damage criteria for residential structures; determination of blasting parameters which grossly affected vibrations; empirical safe blasting limits; and the problem of human response. While values of 2.0 In/sec particle velocity and 0.5 Psi air blast overpressure are recommended as safe blasting limits not to be exceeded to preclude damage to residential structures, lower limits are suggested to minimize complaints. Millisecond-delay blasting is shown to reduce vibration levels as compared to instantaneous blasting, and electric cap delay blasts offer a slight reduction in vibration levels as compared to primacord delay blasts. Vibration levels of different blasts may be compared at common scaled distances, where scaled distance is the distance divided by the square root of the maximum charge weight per delay. Geology, rock type, and direction affect vibration level within limits. Empirically, a safe blasting limit based on a scaled distance of 50 ft/lb1/2 may be used without instrumentation. However, a knowledge of the particle velocity propagation characteristics of a blasting site determined from instrumented blasts at that site are recommended to insure that the safe blasting limit of 2.0 In/sec is not exceeded. (Out of print.)

19710101

IH;

1971

PB-231971

A07

B 656

NTIS: PB 231 971