Development of the multi-level displacement sensor using Fiber Bragg Gratings (FBG)

Sanada, Hiroyuki; Sugita, Yutaka; Daimaru, Shuji; Matsui, Hiroya; Kashiwai, Yoshio*

Journal of MMIJ, 126(10,11), p.569 - 576, 2010/10

When the structures such as rock slopes, underground caverns for the geological disposal of high level radioactive waste and underground power plants are constructed, the potential for displacement and damage in the surrounding rock mass is increased due to stress concentration and creep phenomenon. Therefore, the long-term monitoring of rock stability for construction of rock cavern and slopes is important to maintain stability of rock structures. Recently, development of sensors that use optical fiber have expanded mainly in the field of civil engineering and, in rock and soil mechanics, since several parameters such as temperature, strain, pressure, pH etc. can be obtained by using backscattered light in optical fibers. Additionally, some important advantages using optical fiber are its high resistance to the electric insulation failure, long-term endurance and ability to transmit data over long distances. This paper describes development of a multiple-type displacement sensor using FBG, which has potential for the long-term durability and high accuracy. Laboratory tests were carried out to investigate the relational expression computed from the relationship of the variation in the Bragg wavelength, temperature and displacement. Accuracy of the prototype developed in this research is better than 0.5% or 1/100 mm. The in situ tests involving long-term monitoring using boreholes were conducted to confirm the workability and applicability of the prototype. From the results of the in situ tests, workability is equivalent to the extensometers usually used for long-term monitoring, and the displacement computed from the variation of Bragg wavelength is almost equal to the artificially induced deformation.

Development of optical fiber displacement sensor for bedrocks (The Second year)

Kashiwai, Yoshio*; Sanada, Hiroyuki; Matsui, Hiroya

JAEA-Technology 2008-046, 52 Pages, 2009/07

JAEA-Technology-2008-046.pdf:37.92MB

This work was performed by Taisei Kiso Sekkei Co., Ltd. under contract with Japan Atomic Energy Agency. The objective of this work is development of multiple stage optical fiber displacement sensors for the deformation monitoring of shafts and horizontal tunnels at the Phase 2 of Horonobe Underground Research Laboratory project. In previous year, the feasibility study was done for developing the multiple stage optical fiber displacement sensors of ten stages or more for the boreholes which diameter are 66 mm. Based on this feasibility study, two types of prototype for field measurement were developed and evaluated by laboratory tests. These prototypes were modified and field test equipments were developed which were consisted of 4 pieces of shallow part sensors and 2 pieces of deep part sensors.

Feasibility study for a multi-level pore water pressure monitoring system using FBG sensors

Takeuchi, Shinji; Kashiwai, Yoshio*; Hirata, Yoichi*; Yoshida, Yukimi*; Nishigaki, Makoto*

Proceedings of 4th IEEE/LEOS Workshop on Fibres and Optical Passive Components (WFOPC 2005), p.393 - 398, 2005/00

A multi-level groundwater monitoring system using FBG sensors has been developed for measuring pore water pressure and temperature in small diameter boreholes. The system consists of packer units, temperature and pressure sensing units, and optical fiber cable connecting units. The system with two measurement sections was established as a prototype for the feasibility study. A preliminary test was carried out for about 11 months in a borehole in the Tono area central Japan. The test data obtained in early period were unstable and periods of data loss occurred. Several improvements were implemented and subsequent results show the developed system is feasible for using in slim boreholes.

Horonobe Underground Research Laboratory Project, Development of techniques for investigating the geoligical environment; Development of extensometer used FBG sensor

Sanada, Hiroyuki; Sugita, Yutaka; Daimaru, Shuji; Matsui, Hiroya; Kashiwai, Yoshio*

no journal, , 

no abstracts in English