ANALYSIS OF BENDER ELEMENT TESTS

A study is presented of potential errors in, and methods of interpreti ng, the results of cantilever-type, piezoceramic bender element tests for measuring the shear wave velocity of laboratory soil specimens. In terpretations based on the first direct arrival in the output signal a re often masked by near-field effects and may be difficult to define r eliably. Interpretations based on characteristic points or crosscorrel ation between the input and output Signals are shown to be theoretical ly incorrect in most cases because of: (1) the effects of wave interfe rence at the boundaries; (2) the phase lag between the physical wave f orms and the measured electrical signals; and (3) non-one-dimensional wave travel and near-field effects. Interpretations based on the secon d arrival in the output signal are theoretically Subject to errors fro m non-one-dimensional wave travel and near-field effects. Differences in V-s values obtained by the different interpretation methods are ill ustrated analytically and experimentally.