A framework interpreting bender element tests, combining time-domain and frequency-domain methods

Bender element (BE) testing is a powerful and increasingly common laboratory technique for determining the shear S-wave velocityof geomaterials. There are several advantages of BE testing, but there is no standard developed for the testing procedures or for the interpretationof the results. This leads to high degree of uncertainty and subjectivity in the interpretation. In this paper, the authors review the most commonmethods for the interpretation of BE tests, discuss some important technical requirements to minimize errors, and propose a practical framework forBE testing, based on the comparison of different interpretation techniques in order to obtain the most reliable value for the travel time. This newprocedure consists of the application of a methodical, systematic, and objective approach for the interpretation of the results, in the time andfrequency domains. The use of an automated tool enables unbiased information to be obtained regarding variations in the results to assist in thedecision of the travel time. Two natural soils were tested: residual soil from Porto granite, and Toyoura sand. Specimens were subjected to the sameisotropic stress conditions and the results obtained provided insights on the effects of soil type and confining stress on the interpretation of BE results;namely, the differences in testing dry versus saturated soils, and in testing uniform versus well-graded soils.