Embedded Quasi-Distributed Fiber-Optic Sensors for the Long-Term Monitoring of the Grouting Area of Rock Anchors in a Large Gravity Dam

Abstract

Steel anchors were installed in a gravity-dam, in order to increase the stability of the dam. Quasi-distributed fiber-optic strain sensors are centrally positioned in the complete length of these anchors to detect the long-term behavior of the tendon bonded to the rock foundation. Because the sensor rod containing the measuring lengths is directly bonded to the grout in the fixed anchor length area, it is able to measure the longitudinal strain distribution in the anchor bond area. Such sensors help to evaluate the bonding of the fixed anchor bond length in a rock or in difficult ground areas.

Design of the anchors, manufacturing and on-site installations are described. The measuring principle and its characteristics are also described. Measured results given show the ability of sensorequipped anchors to monitor the tendon bond behavior over a period of years. Results four years after sensor system installation are presented.

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References

Edertalsperre 1994. Festschrift der Wasserund Schiffahrtsdirektion Mitte, 1994. 141 pages.

Feddersen, I. 1986. "Untersuchungen bei der Standsicherheitsiiberpriifung der Ederund Diemeltalsperre". Geotechnik, Sonderheft 1987 zum 7. Nationalen Felsmechanik-Symposium, Aachen, Febr. 1986, p. 221-228, ISSN 0172-6145

Feddersen, I. et al. 1992. "Instandsetzung der Staumauer der Edertalsperre" (Rehabilitation of the Eder-dam). Wasserwirtschaft 82, Heft 2, p. 62-72, ISSN 0043-0978

Feddersen, I. 1997. "Improvement of the Overall Stability of a Gravity-dam with 4500 kN-anchors".. Proceedings of the International conference on Ground Anchorages and Anchored Structures organized by the Institution of Civil Engineering. London, UK. March 1997, Edited by G. S. Littlejohn. Thomas Telford , ISBN: 0 7277 2607 2

Kóhler, H. -J. and I. Feddersen 1991. Proceedings of the 3rd International Symposium on Field Measurements in Geomechanics. Oslo, Norway. Sept. 1991, Edited by Geraldine Sorum , NGI , Balkema , Rotterdam , p. 107-116, ISBN 90 5410 0265

Technical Report BAM-S.12 1998. "Messung der LWL-Sensoren an den Ankern in der Ederstaumauer..." (Measurement of Fiber Sensor's Strain Stage in the anchors of the Eder dam), (unpublished).

Wolff, R. and H. -J. Miefieler 1992. "Novel optical fibre Sensors for Monitoring Structures, Rock and Earth Bolts and measured Sections in Rock," Felsbau No. 5, 223-227.

Zimmermann, B. D. et al. 1990. "Fiber-Optic Sensors Using High-Resolution Optical Time Domain Instrumentation Systems," J of Lightwave Technology, 8(9), 1273-1277.