## 1 Introduction  
There exist few studies related to using fiber Bragg grating sensor technology to perform structural health monitoring for hydraulic structures in a harbor, as well as on mechanical performance monitoring during the pile driving process. A wharf is one of the most important hydraulic structures in seaports, and piles are key components of a high-piled wharf to support the service load. Therefore,studying the performance of the mechanics during the pile driving process is the key means to determining the mechanic status to maintain the safety of the wharf. A high-piled wharf structure is one of most important types of wharf structures and is widely adopted in ports with soft soil foundations. However, with soil creep, the lateral displacement of the wharf increases under the service loads, which will cause damage in the wharf structure. Therefore, conducting mechanical performance monitoring of piles when pile driving is an important means to determine the original mechanical status of the structure, which is beneficial in assessing the safety of the wharf. At present, optical fiber sensors are most often used in structural mechanical performance testing [1; 2; 3]. Particularly, an optical-fiber Bragg grating (FBG) sensor is used to monitor the structural strain, temperature, angle, and so on [4; 5]. Writing Bragg gratings into the core of a fiber was first demonstrated by [PERSON] et al. [6]. The fabrication of fiber Bragg gratings in a fiber core was reported in 1989, which was a significant milestone for fiber Bragg grating (FBG) sensor development [7]. The working principle of FBG sensors is that a series of parallel gratings is printed into the core of an optical fiber, and a specific wavelength of light is reflected from the sensors when a broadband light illuminates them. Since the wavelength reflected at the peak is proportional to the grating period, the axial strain can be measured through the peak shift and temperature. FBG sensors are immune to electromagnetic noise and radio interference [2]. The ability to resist corrosion makes FBG sensors durable. The multiplexing capability and wavelength-encoded measure and information are distinct advantages of FBG sensors compared to other types of fiber optic sensors. FBG sensors can be easily multiplexed with a single string of optical fiber, which can accommodate tens of FBG sensors. In particular, FBG sensors are non-conductive and not significantly affected by water, so they are suitable for use in infrastructure served in the sea, whereas traditional electrical sensors have difficulty performing in water environments for extended periods of time. In this regard, the application of this new technology will lead to a significant improvement in the accuracy of measurements [8]. However, the most common method for pile dynamic testing currently is to monitor driving with the PDA, and the method has gained wide acceptance given the clear advantages in terms of time and cost [9]. The practical application of FBG sensors to actual port engineering structures has not been widely adopted, especially in pile driving monitoring, although the progress of fiber optic measurement is impressive [10; 11; 12]. There are few articles reporting pile mechanical performance during driving using the FBG sensor technique. The main purpose of this paper is to describe mechanical performance monitoring using the FBG sensor technique and analysis results of prestressed concrete piles during pile driving, which are driven for a newly-built high-piled wharf structure located in the Tianjin port of China. The wharf, which is named South 27# Wharf, is 390 m long and 75 m wide. It will be used for ore transportation and other bulk cargo shipping. The fiber-laser-based wavelength-division-multiplexed (WDM) FBG sensor interrogation techniques will be used in the project. The FBG strain sensors and FBG angle sensor are embedded in the body of precast prestressed concrete piles to measure the strain and obliquity angle data of the pile during driving.