4.4. Deformation and Shear Wave Monitoring

The LVDT (TransTek DC 0242, Trans-Tek, Inc., Ellington, CT, USA) connected to a da-ta logger (Keysight 34970A, Keysight Technologies, Santa Rosa, CA, USA) and computer, as shown in Figure 7, continuously monitors the vertical deformation of specimens during the loading procedure. This study selects a parallel type of bender elements to generate and detect shear waves and minimize the effect of crosstalk [36]. The dimensions of bender elements are 12.7 × 8.0 × 0.7 (length × width × thickness in mm) with a 5.0-mm cantilever length. The function generator forms step input signals with a 10-V input voltage (Keysight 33210A, Keysight Technologies, Santa Rosa, CA, USA), and elastic shear waves transformed by the bender element then propagate through the soils. The filter ampli-fier (Krohn-Hite 3364, Krohn-Hite Corporation, Brockton, MA, USA) uses 500 Hz and 200 kHz for high- and low-pass filtering, respectively. The computer saves the signals shown on the oscilloscope (Keysight DSOX 2014A). The minimum sampling frequency of received signals is 1 MHz. The number of signals stacked for a high signal-to-noise ratio is 1024 [37]. The shear wave signals are saved at the end of each loading stage when the deformation reaches an asymptote.