Distributed fibre-optic monitoring of an Osterberg-cell pile test in London

Pelecanos, Loizos; Soga, Kenichi; Chunge, Musa P.M.; Ouyang, Yibo; Kwan, Vivien; Kechavarzi, Cédric; Nicholson, Duncan

doi:10.1680/jgele.16.00081

Cited by 38 publications

(14 citation statements)

References 25 publications

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“…However, BOTDR/A is also applicable to the distributed strain monitoring of a well (Klar et al, 2019). In the construction industry, BOTDR/ A has been used for the deformation monitoring of pile foundations (Klar et al, 2006;Bourne-Webb et al, 2009;Mohamad et al, 2011;Pelecanos et al, 2017Pelecanos et al, , 2018. Although monitoring of a pile is analogous to monitoring of a well, the lengths are significantly different: the latter is much deeper (up to 10,000 m) than the former (up to 100 m).…”

Section: Monitoring Of Axial Strain Development Of the Well Modelmentioning

confidence: 99%

Distributed fibre optic strain sensing of an axially deformed well model in the laboratory

Sasaki

Park

Soga

et al. 2019

Journal of Natural Gas Science and Engineering

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Well integrity is crucial in enabling sustainable gas production from methane hydrate reservoirs and real-time distributed monitoring techniques can potentially facilitate proper and timely inspection of well integrity during gas production. In this research, the feasibility of distributed fibre optic strain monitoring with Brillouin optical time domain reflectometry/analysis (BOTDR/A) for well monitoring was examined by conducting a laboratory test on a well model subjected to axial tensile deformation, which occurs due to reservoir compaction during gas production. First, the validity of the proposed experimental methodology is assessed by a finite element analysis and theoretical modelling of a well subjected to reservoir compaction. A 3 m long well model is developed from the modelling and is instrumented with different types of fibre optic cables to measure the distributed strain development during tensile loading. Results show that the proposed well model and loading scheme can satisfactorily simulate the axial tensile deformation of the well in the laboratory condition. BOTDR is 1 capable of capturing the tensile strain development of the well model accurately within the limitation of the spatial resolution of the BOTDR measurement. To enable accurate distributed strain monitoring of well deformation with BOTDR/A, the following issues are discussed: tightly buffered coating layers around optical fibre cores through mechanical compression and/or chemical adhesion, and a small number of coating layers.

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Section: Monitoring Of Axial Strain Development Of the Well Modelmentioning

confidence: 99%

Distributed fibre optic strain sensing of an axially deformed well model in the laboratory

Sasaki

Park

Soga

et al. 2019

Journal of Natural Gas Science and Engineering

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“…Fibre Bragg Gratings (FBG) (Kersey & Morey 1993;Lee et al 2004;Liu & Zhang 2012;Doherty et al 2015) and distributed Brillouin Optical Time-Domain Reflectometry (BOTDR) (Kurashima et al 1993;Soga 2014;Pelecanos et al 2017). The latter technology offers near spatially-continuous strain data along the entire length of the pile, which can be further processed to provide detailed information regarding the pile behaviour and integrity and load-transfer properties de Battista et al 2016).…”

Section: Recent Advances In Geotechnical Instrumentation Include Fibrmentioning

confidence: 99%

Distributed Fiber Optic Sensing of Axially Loaded Bored Piles

Pelecanos

Soga

Elshafie

et al. 2018

J. Geotech. Geoenviron. Eng.

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Instrumented pile tests are vital to establish the performance of a pile and validate the assumptions made during initial design. Conventional instrumentation includes vibrating wire strain gauges and extensometers to measure the change in strain or displacements within a pile. While these strain and displacement gauges are very accurate, they only provide strain/displacement readings at discrete locations at which they are installed. It is therefore common to interpolate between two consecutive points to obtain the values corresponding to the data gaps in between; in practice, these discrete instrumented points could be tens of Manuscript Click here to download Manuscript Pelecanos_et_al_Manuscript_7.2.docx 2 meters apart, at depths corresponding to different soil layers, and hence simple interpolation between the measurement points remains questionable. The Brillouin Optical Time Domain Reflectometry fibre optic strain sensing system however is able to provide distributed strain sensing along the entire length of the cable, enabling the full strain profile to be measured during a maintained pile load test. The strain data can also be integrated to obtain the displacement profile. In this paper, three case studies are presented where the performance of three concrete bored piles in London is investigated using both conventional vibrating wire strain gauges and distributed fibre optic strain sensing during maintained pile load tests which enabled comparisons to be made between the two instrumentation systems. In addition, finite element analyses were conducted for the three piles and it was found that the ability to measure the full strain profiles for each pile is highly advantageous in understanding the performance of the pile and in detecting any abnormalities in the pile behaviour.

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“…The frequency in both cables can be measured simultaneously by splicing the cables into a single loop to avoid multiplexing through multiple channels. No strain data is used in this study and the strain data obtained during pile load test data is presented in details in Pelecanos et al [ 23 ]. Hence, Equation (3) is used to solely calculate temperature changes during concrete curing at every sampling point to construct temperature profiles.…”

Section: Measuring Principle Of the Fibre Optic Sensing Technique mentioning

confidence: 99%

“…Distributed fibre optic sensing (DFOS) is gaining prominence in the field of structural health monitoring because of several advantages such as high spatial density of data, ease of installation and reliability. It has been used successfully in several applications such as monitoring the performance of ageing or new tunnels [ 13 , 14 , 15 ]; the behavior of thermal pile under coupled mechanical and thermal load [ 16 , 17 , 18 , 19 ]; displacement of diaphragm walls induced by excavation [ 20 ]; strain and crack of concrete pavement [ 21 ]; initiation and propagation of delamination of ultra-highperformance concrete overlay [ 22 ]; and is now regularly used as the preferred method for preliminary pile load tests [ 23 ].…”

Section: Introductionmentioning

confidence: 99%

Integrity Testing of Pile Cover Using Distributed Fibre Optic Sensing

Rui

Kechavarzi

O'Leary

et al. 2017

Sensors

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The integrity of cast-in-place foundation piles is a major concern in geotechnical engineering. In this study, distributed fibre optic sensing (DFOS) cables, embedded in a pile during concreting, are used to measure the changes in concrete curing temperature profile to infer concrete cover thickness through modelling of heat transfer processes within the concrete and adjacent ground. A field trial was conducted at a high-rise building construction site in London during the construction of a 51 m long test pile. DFOS cables were attached to the reinforcement cage of the pile at four different axial directions to obtain distributed temperature change data along the pile. The monitoring data shows a clear development of concrete hydration temperature with time and the pattern of the change varies due to small changes in concrete cover. A one-dimensional axisymmetric heat transfer finite element (FE) model is used to estimate the pile geometry with depth by back analysing the DFOS data. The results show that the estimated pile diameter varies with depth in the range between 1.40 and 1.56 m for this instrumented pile. This average pile diameter profile compares well to that obtained with the standard Thermal Integrity Profiling (TIP) method. A parametric study is conducted to examine the sensitivity of concrete and soil thermal properties on estimating the pile geometry.

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Distributed fibre-optic monitoring of an Osterberg-cell pile test in London

Cited by 38 publications

References 25 publications

Distributed fibre optic strain sensing of an axially deformed well model in the laboratory

Distributed fibre optic strain sensing of an axially deformed well model in the laboratory

Distributed Fiber Optic Sensing of Axially Loaded Bored Piles

Integrity Testing of Pile Cover Using Distributed Fibre Optic Sensing

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