A Method for Received Waveform Reconstruction Based on Bender Element Test Using Frequency-swept Signal

Abstract

An experimental technique for reconstructing the received wave of bender element tests based on linear system theory is shown in this paper. In order to identify the frequency response of testing apparatus, bender element tests using frequency-swept signals are performed. Received waves for one-period sine pulse transmitting with various frequencies are calculated and compared with observed waves in several kinds of soil samples and testing apparatuses. The linearity of the testing system is also conˆrmed by coherence function. It is shown that calculated data are less aŠected by random noise and show good agreement with observed data in regards to not only waveform itself but also resulting shear wave velocity. It is mentioned that this technique can provide simulations for arbitrary transmitted waveform with high signal/noise ratio after laboratory tests are performed. It is also mentioned that this technique is advantageous when su‹cient amplitude of received wave cannot be ensured or shear wave velocity must be veriˆed, for example, due to uncertainty of arrival time by near-ˆeld eŠect.

Frequency Response Characteristics of Bender Element Test System Identified by Frequency-Swept Signal Input —Influence on Accuracy of Received Waveform Reconstruction—

“…(8). Figure 11 summarizes values of R(0) for one-period sine inputs of 10 kHz as well as 3, 5, 15 and 20 kHz.…”

“…According to Ogino et al (2008), the received waveform of bender element test can be expressed by following equation:…”

“…Even though some approaches to detect reasonable value have been proposed so far (e.g., Viggiani and Atkinson, 1995; Greening and Nash, 2004), oneperiod sine wave of which frequency is determined by trial-and-error to cancel near-ˆeld eŠect is still applied to input waveform to estimate reasonable arrival time. Meanwhile, the authors have proposed so far an alternative method which reconstructs received waveform for any input wave by operating convolution of frequency response of bender element test system and the input waveform and demonstrated the waveform reconstruction on several apparatuses of which frequency responses were identiˆed by frequency-swept signal (Ogino et al, 2008). Frequency response of a system being independent of the input waveform, this method allows experimenters to restore the received wave and estimate the travel time for any input wave after experiments were implemented.…”