## 3 Modelling of Wave Propagation in Wooden Poles
### Experimental Validation  
To validate the performance of the FE model to describe the wave propagation in the wood poles with surrounding soil, the laboratory testing is conducted to make the comparison with simulation results. In this study, a 5 m long pole embedded in sand by 1 m is employed due to the limitation of the ceiling height in the laboratory. The dimensions of the cage that stores the sands are 1.2 m by 1.3 m by 3 m, in which 3 m is the height of the cage. Figure 6 gives the makeup of NDE system for pole testing, which consists of a modally tuned impact hammer, multiple sensors (accelerometers), a multi-channel signal conditioner, a multi-channel data acquisition system and a computer equipped with signal acquisition software. For the guided wave testing, the adopted impact hammer (PCB Piezotronics, Depew, NY, USA) is a PCB model HP086C05 of sensitivity 0.24 mV/N. A load cell connected with hammer is used to measure the impact force to the structure. To record the structural response, piezoelectric accelerometers (PCB Piezotronics, Depew, NY, USA) with PCB model 352C34 are employed, which have the high sensitivity of 100 mV/g as well as the bandwidth from 0.2 Hz to 10 kHz. To amplify and tune the signals of the modal hammer and the piezoelectric accelerometers, a 12-channel signal conditioner (PCB Piezotronics, Depew, NY, USA) with model PCB 483B03 is utilised. The data acquisition system (National Instruments, Austin, TX, USA) employed is a middle range 8-channel system with 12-bit 4 M sample/sec per channel with model NI PCI6133. In this work, the sample frequency for NDE of wood pole is set as 1 MHz. For data processing and analysis, a personal computer (Dell Inc., Round Rock, TX, USA) equipped with NI software LabVIEW (National Instruments, Austin, TX, USA) is adopted.  
Experimental setup and the FE model designed by ANSYS (ANSYS Inc., Canonsburg, PA, USA) are given in Figure 7. In this comparative study, both frictional contact and bonded contact are  
Figure 6: Testing equipment: (**a**) Impact hammer; (**b**) Accelerometers; (**c**) Signal conditioner; (**d**) Data acquisition system; (**e**) Laptop with LabVIEW.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Property** & **Pole** & **Bedrock** & **Steel Cable** \\ \hline Elastic modulus (MPa) & 23,000 & 32,000 & 210,000 \\ Density (kg/m\({}^{3}\)) & 950 & 2400 & 7850 \\ Poisson’s ratio & 0.3 & 0.2 & 0.2 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Material properties for three structural components.  
To get the optimal material model representing the wood pole, further validation is conducted, in which isotropic, orthotropic and transversely isotropic material models are created and compared with experimental results. Figure 10 gives the corresponding response results obtained from the sensor located at 1.6 m from the bottom of the pole. It is noticeable that the wave responses of isotropic material model and transversely isotropic material model are quite close to each other for both wave pattern and time when the peaks appear. It also can be observed that even though the response of orthotropic material model misses some clear peaks, the times when peaks appear are more consistent with experimental results than other material model.