## 3 Data Acquisition and Analysis  
In the testing, one pile's embedded sensors were chosen to measure the dynamic response during pile driving in situ. Performance monitoring of the pile was conducted during pile driving with the piling hammer (the energy of each impact was 461 kJ) at the seaside of Tianjin Port. The distance between two concrete piles was 4.42 m. By comparing the results obtained through the different sensors, the difference between each sensor can be obtained and each sensor can be verified. The pile will be maintained in four location states during the entire pile driving process, which are flat in shipment, upright for diving, driving, and ending, as shown in Figure 9. The mechanical states are different in different location states. We collected all of the data for the pile being maintained in the different location states. Then, the dynamic response testing of the pile was conducted during pile driving, and the time history of the vibration response under the impact of the piling hammer was obtained. The time history of data from all sensors is shown in Figure 10 with the unit of wavelength. The FBG strain sensor used in the testing is a new type sensor that is less thermosensitive and does not require temperature compensation, while the FBG angle sensor does include temperature compensation. There are five  
Figure 8: Transducer setup. Figure 9: Pile driving process. curve lines in total in Figure 10. The Head, Mid, Tip, A-temp, and Angle represent the strain at the head of pile, strain at the middle of the pile, strain at the tip of pile, temperature compensation for the angle sensor, and angle measurement, respectively. Based on the curve lines of the angle sensor, the entire time history of strain can be clearly divided into four stages, which is consistent with the pile driving steps. Meanwhile, the data from the pile from flat to upright were also collected, as shown in Figure 11. From the time history of strain near the tip, it can be seen that there is a saltation of the wavelength. This occurs because the weight of the pile affects its tip, creating a compressive stress, which is consistent with the pile driving process. To obtain the strain state of the pile and propagation law of the stress wave during pile driving, the wavelength data of the strain sensor were converted to strain data, which are shown in Figure 12. Due to the change of angle being so small during pile driving, it is not discussed here and is only used to distinguish the strain data in the different stages mentioned above. Figure 11: Time history of the strain of the pile from flat to upright. Figure 10: Time history of vibration data during the entire pile driving process. As seen from Figure 12, the compressive strain at the middle of the pile is larger than that at the head and tip of the pile. This phenomenon occurs due to the eccentric compression of the pile caused by the piling hammer's eccentric impacting. Eccentric impacting to the head of the pile will create the largest bent moment at the middle of the pile and generate the largest compressive strain at the middle of the pile. Thus, the middle of the pile is the key location that should be monitored preferentially during pile driving. Figure 12: Time history of pile strain during driving. It can also be seen from Figure 12 that the tension strain increases at the middle and tip of the pile during the several impacts at the beginning. Since the pile will have an upward movement after hammer impacting, it functions like particle vibration. In the process of the pile moving up, the body of the pile will be tensed due to the frictional resistance of the soil. During the first several hammer impacts, the tension strain at the middle and tip of the pile became larger, and after the fifth impact in Figure 12, the tension decreased. This is just the process of the pile passing through the first supporting soil layer, and when the pile passes through the soil layer, the frictional resistance became larger.