Time and frequency domain evaluation of bender element systems

Abstract

Bender elements are used to measure the low-strain shear-wave velocity of soils in many geotechnical laboratories worldwide. Despite their popularity, the method remains without a standard, mainly owing to the difficulties in controlling the actual behaviour of the bender element inside the specimen. Previous experimental and analytical studies on the behaviour of bender elements have found evidence that the actual transmitter movement is not equal in shape or frequency content of the electrical signal used as the input excitation. Furthermore, the size and geometry of the specimen influence the response of these piezoelectric transducers. In this study, miniature accelerometers are used to measure the particle vibration inside specimens during bender elements tests, which were performed in a resonant column device. The comparison between shear wave velocities obtained by resonant column and miniature accelerometers tests allow a better interpretation of bender element testing. The sine pulse bender element test results showed good agreement with the resonant column measurements. The results show the importance of the resonant frequencies of the bender element and their influence on frequency domain analysis of bender element testing.