A Framework Interpreting Bender Element Tests, Combining Time-Domain and Frequency-Domain Methods

Abstract

ABSTRACT:Bender element (BE) testing is a powerful and increasingly common laboratory technique for determining the shear S-wave velocity of geomaterials. There are several advantages of BE testing, but there is no standard developed for the testing procedures or for the interpretation of the results. This leads to high degree of uncertainty and subjectivity in the interpretation. In this paper, the authors review the most common methods for the interpretation of BE tests, discuss some important technical requirements to minimize errors, and propose a practical framework for BE testing, based on the comparison of different interpretation techniques in order to obtain the most reliable value for the travel time. This new procedure consists of the application of a methodical, systematic, and objective approach for the interpretation of the results, in the time and frequency domains. The use of an automated tool enables unbiased information to be obtained regarding variations in the results to assist in the decision of the travel time. Two natural soils were tested: residual soil from Porto granite, and Toyoura sand. Specimens were subjected to the same isotropic 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.

Characterization of Soil Treated With Alkali-Activated Cement in Large-Scale Specimens

“…The equipment consists of a pair of compression transducers and a pair of shear transducers, a pulse waveform generator, and data acquisition unit equipped with an amplifier connected to a personal computer with specific software to operate as an oscilloscope. Based on the propagation times evaluated with a time domain approach (Viana da Fonseca et al 2009;Rios et al 2016b), the wave velocities (V P and V S , respectively for P and S waves) were determined dividing the height of the specimen by the time. From the results of the seismic wave's velocities, the evolution of the dynamic Young's Modulus (E 0 ) was obtained according to the following elasticity theory equations:…”

“…The soil used in this work was a well-graded remolded residual silty sand from granite already studied in detail in its natural and remolded conditions (Viana da Fonseca 2006, 2013bCruz 2010). Tables 1 and 2 present the results of identification and compaction tests performed in the remolded soil, as well as the compaction results for the mixture of soil with 20 % of fly ash.…”

Mechanical and durability properties of a soil stabilised with an alkali-activated cement

“…The interpretation to identify the wave travel time (t) is based on time domain approach, according to Viana da Fonseca et al (2009). Wave velocities are then calculated dividing the specimen length (which corresponds to the travel distance) by the corresponding travel time.…”

Bender elements in stiff cemented clay: shear wave velocity (Vs) correction by applying wavelength considerations

“…By using the time difference between characteristic peaks or troughs in input and output signals, Δt can also be determined. However, signal attenuation and material damping cause the output signals to be no longer identical to input signals which reduces the reliability of this technique (Arulnathan et al 1998;Khan et al 2017;Vianna da Fonseca et al 2009). Cross correlation is an automated technique that utilizes a function which measures the degree of similarity between input and output signals.…”