Distributed fiber optic monitoring of a CFA pile with a central reinforcement bar bundle

Abstract

In this paper, we present an application of distributed fiber optic sensor (DFOS) technology to measure the strain of a continuous flight auger (CFA) test pile with a central reinforcement bar bundle, during a static load test carried out in London. Being distributed in nature, DFOS gives much more information about the pile performance as compared to traditional point sensors, such as identifying cross-sectional irregularities or other anomalies. The strain profiles recorded along the depth of the piles from the DFOS were used to calculate pile deformation (contraction), shaft friction, and tip resistance under various loads. Based on this pile load test, a finite element (FE) analysis was performed using a one-dimensional nonlinear load-transfer model. Calibrated by the shaft friction and tip resistance derived from the monitored data, the FE model was able to simulate the pile and soil performance during the load testing with good accuracy. The effect of the reinforcement cage and central reinforcement bar bundle were investigated, and it was found that the addition of a reinforcement cage would reduce the pile settlement by up to 20%.

Keywords

continuous flight auger pile / static load test / central reinforcement bar bundle / distributed fiber optic sensor / finite element / load transfer

References

[1] British Standards Institution. BS EN 1997-1:2004+A1:2013 Eurocode 7. Geotechnical Design, General Rules. London, UK: BSI, 2004

[2] Bond A J, Jardine R J, Dalton J C P. Design and performance of the Imperial College instrumented pile. Geotechnical Testing Journal, 1991, 14(4): 413–424

[3] Ismael N F. Axial load tests on bored piles and pile groups in cemented sands. Journal of Geotechnical and Geoenvironmental Engineering, 2001, 127(9): 766–773

[4] Brown M J, Hyde A F L, Anderson W F. Analysis of a rapid load test on an instrumented bored pile in clay. Geotechnique, 2006, 56(9): 627–638

[5] Jardine R J, Zhu B T, Foray Y Z X. Interpretation of stress measurements made around closed-ended displacement piles in sand. Geotechnique, 2013, 63(8): 613–627

[6] Jardine R J, Zhu B T, Foray P, Yang Z X. Measurement of stresses around closed-ended displacement piles in sand. Geotechnique, 2013, 63(1): 1–17

[7] McNamara A M, Suckling T, McKinley B, Stallebrass S E. A field trial of a reusable, hollow, cast-in-situ pile. Geotechnical Engineering, 2014, 167(4): 390–401

[8] Kechavarzi C, Pelecanos L, de Battista N, Soga K. Distributed fibre optic sensing for monitoring reinforced concrete piles. Geotechnical Engineering Journal of the SEAGS & AGSSEA, 2019, 50(1): 43–51

[9] Institution of Civil Engineers (Great Britain). ICE Specification for Piling and Embedded Retaining Walls. London: ICE Publishing, 2016

[10] Lee W, Lee W J, Lee S B, Salgado R. Measurement of pile load transfer using the Fiber Bragg Grating sensor system. Canadian Geotechnical Journal, 2004, 41(6): 1222–1232

[11] Kister G, Winter D, Gebremichael Y M, Leighton J, Badcock R A, Tester P D, Krishnamurthy S, Boyle W J O, Grattanb K T V, Fernando G F. Methodology and integrity monitoring of foundation concrete piles using Bragg grating optical fibre sensors. Engineering Structures, 2007, 29(9): 2048–2055

[12] Majumder M, Gangopadhyay T K, Chakraborty A K, Dasgupta K, Bhattacharya D K. Fibre Bragg gratings in structural health monitoring—Present status and applications. Sensors and Actuators. A, Physical, 2008, 147(1): 150–164

[13] Doherty P, Igoe D, Murphy G, Gavin K, Preston J, McAvoy C, Martin C M. Field validation of fibre Bragg grating sensors for measuring strain on driven steel piles. Géotechnique Letters, 2015, 5(2): 74–79

[14] Bao X, DeMerchant M, Brown A, Bremner T. Tensile and compressive strain measurement in the lab and field with the distributed Brillouin scattering sensor. Journal of Lightwave Technology, 2001, 19: 1698–1704

[15] Cui Q, Pamukcu S, Xiao W, Guintrand C, Toulouse J, Pervizpour M. Distributed fiber sensor based on modulated pulse base reflection and Brillouin gain spectrum analysis. Applied Optics, 2009, 48(30): 5823–5828

[16] Cui Q, Pamukcu S, Lin A, Xiao W, Toulouse J. Performance of double side band modulated probe wave in BOTDA distributed fiber sensor. Microwave and Optical Technology Letters, 2010, 52: 2713–2717

[17] Cui Q, Pamukcu S, Lin A, Xiao W, Herr D, Toulouse J, Pervizpour M. Distributed temperature-sensing system based on Rayleigh scattering BOTDA. IEEE Sensors Journal, 2011, 11(2): 399–403

[18] Pamukcu S, Cetisli F, Texier S, Naito C, Toulouse J. Dynamic strains with Brillouin scattering distributed fiber optic sensor. GeoCongress, 2006, 187: 31–36

[19] Cheung L L K, Soga K, Bennett P J, Kobayashi Y, Amatya B, Wright P. Optical fibre strain measurement for tunnel lining monitoring. Proceedings of the Institution of Civil Engineers-Geotechnical Engineering, 2010, 163(3): 119–130

[20] de Battista N, Elshafie M, Soga K, Williamson M, Hazelden G, Hsu Y S. Strain monitoring using embedded distributed fibre optic sensors in a sprayed concrete tunnel lining during the excavation of cross-passages. In: Proceedings of the 7th International Conference on Structural Health Monitoring and Intelligent Infrastructure (SHMII7). Torino: Curran Associates, Inc., 2015: 1–3

[21] Kechavarzi C, Soga K, de Battista N, Pelecanos L, Elshafie M Z E B, Mair R J. Distributed Fibre Optic Strain Sensing for Monitoring Civil Infrastructure. London: Thomas Telford, 2016: 241–246

[22] Mohamad H, Bennett P J, Soga K, Mair R J, Bowers K. Behaviour of an old masonry tunnel due to tunnelling-induced ground settlement. Geotechnique, 2010, 60(12): 927–938

[23] Rui Y, Kechavarzi C, O’Leary F, Barker C, Nicholson D, Soga K. Integrity testing of pile cover using distributed fibre optic sensing. Sensors (Basel), 2017, 17(12): 2949

[24] Schwamb T, Soga K, Mair R J, Elshafie M Z, Boquet C, Greenwood J. Fibre optic monitoring of a deep circular excavation. Geotechnical Engineering, 2014, 167(2): 144–154

[25] Garus D, Golgolla T, Krebber K, Schliep F. Brillouin optical frequency-domain analysis for distributed temperature and strain measurements.  Journal of Lightwave Technology,  1997,  15: 654–662

[26] Horiguchi T, Kurashima T, Tateda M. Tensile strain dependence of Brillouin frequency shift in silica optical fibers. IEEE Photonics Technology Letters, 1989, 1: 107–108

[27] Kurashima T, Horiguchi T, Tateda M. Thermal effects on the Brillouin frequency shift in jacketed optical silica fibers. Applied Optics, 1990, 29: 2219–2222

[28] de Battista N, Kechavarzi C, Soga K. Distributed fiber optic sensors for monitoring reinforced concrete piles using Brillouin scattering. In: Proceedings of the European Workshop on Optical Fibre Sensors-EWOFS 2016. Limerick: SPIE, 2016

[29] de Battista N, Kechavarzi C, Seo H, Soga K, Pennington S. Distributed fibre optic sensors for measuring strain and temperature of cast-in-situ concrete test piles. In: Proceedings of the International Conference on Smart Infrastructure and Construction (ICSIC). London: ICE Publishing, 2016

[30] Pelecanos L, Soga K, Elshafie M Z, de Battista N, Kechavarzi C, Gue C Y, Seo H J. Distributed fiber optic sensing of axially loaded bored piles. Journal of Geotechnical and Geoenvironmental Engineering, 2017, 144(3): 04017122

RIGHTS & PERMISSIONS

The Author(s) 2021. This article is published with open access at link.springer.com and journal.hep.com.cn