Evaluation of the Drop Bar Test for Concrete and Rock Quality

The bearing capacity of rock foundations is being determined by the sound produced by impacting the foundations with a steel bar. This paper evaluates the sound and stress produced. Instrumenting the steel drop bar extends the capabilities of the test and makes the test less subjective. The steel bar produced a characteristic ringing sound when the specimen´s unconfined compressive strength was greater than 5000 kPa or the compressional wave velocity was greater than 2400 m/s. The research suggests that the peak stress and sound frequency produced by dropping a steel bar can be used to evaluate in situ dynamic properties and, indirectly, in situ static properties of concrete and rock. A potential limitation of the noninstrumented bar is that the frequency of ringing (1770 to 10 070 Hz) is in the same frequency range that sensorineural hearing losses are known to occur with advancing age or noise exposure.

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