Innovations in Micropile Testing Using Distributed Optical Fibre Sensors

Abstract

Micropiles are primarily used in situations where traditional foundation methods, such as large-diameter bored piles or driven piles, are not feasible due to various constraints, including limited access, low headroom, or the need to work in environmentally sensitive areas. They are often employed in urban areas with restricted space or for underpinning existing structures. Two case studies of instrumented micropiles are presented in this paper, with the aim to showcase innovations in pile testing using Distributed Optical Fibre Sensing (DOFS). In the first project, micropiles were installed as part of an underpinning work where several existing piles were removed to allow safe passage of Tunnel Boring Machine (TBM) underneath the building. An experiment pile was instrumented with conventional and DOFS sensors to measure pile responses due to tunnelling in proximity. In the second project, the micropile was tested to determine its load carrying capacity for buildings constructed in hilly area. In both cases, API pipes were applied and socketed into bedrocks. Optical cables were attached on four sides of the steel pipes and subsequently grouted. During the load tests, DOFS data were able to display precisely the shaft distribution of micropiles when subjected to vertical loads as well as bending behaviour due to the close proximity tunnelling. Interpretations of distributed strain profiles from DOFS have contributed to a better understanding of API-reinforced micropile performance under complex geological and loading conditions.