Abstract：Research purposes: Optical fiber sensing technology is a new technology of monitor supervises. The newly built Chongwenmen station of Beijing Subway Line 5 goes under the already running line. In order to control the displacement of soil layer, it is needed to test the strain of the pre-braced major diameter pipe umbrella in the construction. The traditional test methods can not satisfy with the requests. Therefore, optical fiber sensing technology is adopted.
Research methods: The optical fiber sensor should be buried before the construction of the pre-braced major diameter pipe umbrella，and some corresponding protective measures should be taken to guarantees that the optical fiber sensor can work well. The pre-braced major diameter pipe umbrella goes against into in the soil layer with optical fiber sensor together, and the strain can be reflected through the optical fiber sensor because it is attached in the pre-braced major diameter pipe umbrella.
Research Conclusions: It is proved that the strain of pipe umbrella can be examined with optical fiber sensor with high precision in the test, and it is more durable and compatible compared to the resistance gages under complex environment. Therefore, the optical fiber sensor technology could be applied in the underground project.
2006, Vol. 23 
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