Validation on laboratory simulated optical fibre sensor instrumented bored pile defect using 3D Finite Element Method

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.

Section: Measurement Resultsmentioning

confidence: 99%

Section: Measurement Resultsmentioning

confidence: 99%

Innovations in Micropile Testing Using Distributed Optical Fibre Sensors

Mohamad,

Tee,

Beddelee

et al. 2023

“…The DFOS instrumentation was commissioned into the pile shaft together with the VWSG. It is obvious that the DFOS provide more data points since it continuously measured the pile response along the shaft which contradicted to discrete VWSG sensor with limited data points [14,15]. Figure 3 and Figure 4 portray the conventional instrumentation arrangement for PTP 1 and PTP 2, respectively.…”

Section: Static Pile Load Testmentioning

confidence: 99%

Instrumented pile load tests in limestones and granite formations - case studies with optical fibre strain sensors

Mohamad,

Beddelee,

Tee

2024

In instrumented pile load tests, obtaining a reliable strain profile is crucial to interpret the load-transfer behaviour of the test pile. For conventional instrumented pile load tests, an extensive quantity of point-based sensors such as vibrating wire strain gauges and tell-tale extensometers were installed to measure strains and pile deformation especially when the test pile is long and with large variation in soil stratum. The advancement of distributed fibre optic sensor (DFOS) technology, has significantly improved the conventional instrumented pile load test method. DOFS based on Brillion Optical Time Domain Analysis (BOTDA) is a novel technique for measuring strains in a continuous manner that outweighs the conventional point-based sensors. A full continuous pile length strain profile minimised misinterpretation of the load-transfer and mobilised shaft friction of the test pile, especially the cast-in-situ pile. This paper discusses two case studies of instrumented pile load tests performed using BOTDA technology for the Klang Valley Mass Rapid Transport (KVMRT) project found in limestones and granite formations. The interpreted results in terms of load transfer response, average unit shaft resistance, and elastic shortening of rock socketing piles are in exceptional agreement with conventional instrumentations such as Vibrating Wire Strain Gauges (VWSG) and Linear Variable Displacement Transducers (LVDT) at 6% difference. The maximum unit shaft friction acquired in the granitic layer was about 2,200 to 2,500 kN/m2 whereas the pile founded in limestones achieved maximum unit shaft friction of 1,800 to 1,900 kN/m2.

“…Processing the raw data of DOFS is vital to appreciate the data for intended usage which involves initial and post-processing. As proven in the wide literature, the DOFS is able to provide information on the structural integrity/health of the measured structure, a great tool [26].…”

Section: Current Dofs Data Processingmentioning

confidence: 99%

Instrumented Pile Load Test: Analysing Measurement Anomaly at the Pile Head

Beddelee,

Mohamad,

Tee

et al. 2024

Loading activity during Distributed Optical Fibre Strain Sensor (DOFS) instrumented pile load test prevails the strain disparity within the pile’s initial depth and converges at a certain depth. This work aims to determine the strain convergence (SC) depth: investigate the influence factor of the SC and propose a standard empirical model for SC depth determination. The strain profile variation at any point within the pile diameter is examined using PLAXIS 2D. A set of test cases are simulated starting with defining influence factors of SC depth and further analysis of the cogent factor. The proposed model is validated to a few real field projects. This work is significant to determine the real start (RS) depth of the plotted strain profile and will improve data processing for the pile load transfer analysis of the DOFS instrumented pile load test. The cogent factor that influences the SC depth is the jack area coverage to pile area and an empirical model is proposed to determine the SC depth. The model is validated to a few real field projects with nominal differences of SC by the model to the field measured at ±0.05 sensitivity, comply the model goodness of fit at 0.9492 (R-square).