###### Abstract  
Acoustic emission (AE) has garnered significant interest as a promising way to detect the early-stage development of internal cracks and damage in underground and geotechnical structures, associated with natural disasters. Meanwhile, AE source localization techniques that can identify the damage location in a piled-raft foundation (PRF) are premature because of its complex geometry, although the PRF is a widely used deep foundation type for high-rise buildings. In this study, we propose an integrated approach to localize AE sources in the PRF by using the modified Akaike information criterion (AIC) method and examine its accuracy to mark with pile zones. We performed a series of experiments on a scaled PRF model at a ratio of 1:50, composed of one raft and 25 piles. The results demonstrate that the combined approach with the modified AIC method and the Simplex method can localize the AE source zones with good accuracy, greater than 95% on average. The suggested two-stage AIC picker shows accurate onset time determination, and hence, it significantly improves the accuracy, particularly effective for the signals with low signal-to-noise ratios. The approach exploiting the two-stage AIC picker can be readily used for automated real-time AE monitoring to detect crack generation and its location in buried foundations that cannot be inspected visually. source localization; acoustic emission; damage; non-destructive test; piled-raft foundation; real-time monitoring; onset time 2020  
000 0000-0000-0000-0000-0000-0000-0000-0000-0000-00000-00000-00000-00000-00000-00000-00000-00000-00000-00000-00000-000000-00000-00000-000000-00000-000  
Meanwhile, real-time and non-destructive structural health monitoring (SHM), which continuously monitors in-service structures and localizes the weakened area in structures, has garnered significant interest in association with frequent occurrences of natural disasters and geohazards [2; 9; 10]. In particular, it is difficult to characterize the damage or defects in underground structures, such as building foundations buried in the subsurface, which are not able to be inspected visually. While it is important to detect the early-stage development of internal cracks, the AE method has been proven as an effective and promising tool for real-time SHM of underground and geotechnical structures. Extensive efforts have been made to apply the AE techniques at a field scale for underground and geotechnical structures, including mines, tunnels, geothermal engineering, and radioactive waste repositories [2; 7; 10; 11; 12; 13]. A piled-raft foundation (PRF) is most widely used for high-rise buildings. However, there have been limited attempts on the AE source localization in the PRF. It is a challenging task because the PRF has a complex geometry composed of a mat (or raft) and a group of piles, as depicted in Figure 1. On the other hand, the precise determination of the onset time of the AE signal has the most pronounced contribution to the accuracy of AE source localization [14; 15; 16]. A group of cracks is simultaneously developed, and thus multiple AE signals are released within a short time frame. Manual determination of the onset time of each signal is time-consuming and less feasible. Additionally, its accuracy can be subjected to the performer's experience. Therefore, automation of onset time determination is one of the critical components in developing real-time AE monitoring while not compromising the accuracy of source localization. Previously, various methods for automatic AE onset time determination have been proposed, which include the fixed amplitude threshold method, short-term average/long-term average (STA/LTA) method, Hinkley criteria, Akaike information criterion (AIC) picker method [17; 18; 19; 20]. However, these automated methods have hardly been implemented nor used for a PRF structure with complex geometry. Figure 1: (a) Monitoring of structural damage at a piled-raft foundation (PRF), and (b,c) schematic diagram of piled-raft foundation (PRF).