the application of distributed optical fiber in high rcc （roller compacted concrete） arch dam proj

1、<p>　　The Application of Distributed Optical Fiber in High RCC （Roller Compacted Concrete） Arch Dam Proj</p><p>　　Abstract. As the highest RCC arch dam under construction around the world， Wanjiakouzi a

2、dopted advanced distributed temperature system （DTS）. This paper summarizes the network design， technical requirements as well as the protection precautions of fiber connector and monitoring port of temperature measureme

3、nt system of optical fiber in high RCC arch dam in Wanjiakouzi. It can be indicated that the accuracy and reliability of DTS by comparing fiber optic temperature values with the conventional t</p><p>　　Key w

4、ords： Distributed optical fiber， Optical fiber sensing， RCC， Temperature monitoring， Arch dam in Wanjiakouzi. </p><p>　　1. Introduction </p><p>　　There is great significance for the measurement

5、of temperature field of high RCC arch dam either in the construction or in the operation. Therefore， to obtain temperature field information within the RCC arch dam timely and accurately is the key to control mass concre

6、te construction. However， the traditional temperature measurement of dam generally uses point-thermometer and mainly relies on thermocouple thermometer which has high accuracy. But as for the practical application of eng

7、ineering， th</p><p>　　Compared with the temperature measurement of conventional thermometer， distributed optical fiber temperature measurement has the advantages of rich measuring points， reflecting the temp

8、erature gradient within the concrete， automatic data acquisition， real-time online monitoring and avoiding man-made accidental errors [1]. DTS is a kind of sensor system for the real-time measurement of spatial distribut

9、ion of temperature field. Through the basic research of British scholars Hartog and Dakin， dist</p><p>　　According to the principles of OTDR and Raman scattering， DTS （Distributed Temperature System） collect

10、s the electric signals of reflected backlight from the temperature information. Then， the WDM， photoelectric detector and signal processor would show the segmental temperature information of optical fiber in a distance o

11、rder from near and far [4] [5]. </p><p>　　The temperature measurement system of optical fiber will emit a beam of pulsed light which will travel forward in a speed slightly lower than the speed of light in v

12、acuum and emit scattered light all around. Part of the scattered light will travel back to the incident end along with the optical fiber. Measure the time difference T between incident light and reflected light， so the d

13、istance X between emitting point of scattered light and incident end is： </p><p>　　Where： C is the speed of light in optical fiber， C=C0/n， C0 is the speed of light in vacuum； n is the refractive index of op

14、tical fiber. </p><p>　　In the reflected lights reflected back into the incident end， one is a known as Raman scattered light which contains two components： Stokes and Anti-Stokes lights. Stokes light is inde

15、pendent of temperature， while the intensity of Anti-Stokes light varies with temperature. The relationship between the ratio of Anti – Stokes and Stokes and temperature can be expressed as follows： </p><p>　

16、　Where： las-Anti-Stokes light； ls-Stokes light； a-Temperature correlation coefficient； h-Planck coefficient， Js； c-Speed of light in vacuum， m/s； v-Raman translation， m-1； k- Bauer watts mann constant， J/k； t-Kelvin rati

17、ng. </p><p>　　Temperature value can be calculated with formula （2） and actual ratio of Stokes-Anti-Stokes lights： </p><p>　　Temperature measurement of optical fiber measures directly the ratio o

18、f the two components in Raman reflected light. It is independent to the absolute value. Therefore， even if the optical fiber is aging over time and the light loss increases along with the way， the effect of light loss ca

19、n also be eliminated， which would ensure the accuracy of temperature measurement. </p><p>　　3. The Application of Distributed Optical Fiber in High RCC （Roller Compacted Concrete） Arch Dam Project </p>

20、<p>　　in Wanjiakouzi </p><p>　　Wanjiakouzi Hydropower Station， located on the Qingshui River at the border of Liupanshui， Guizhou Province and Xuanwei， Yunnan Province， is the fourth cascade hydropowe

21、r station on the main stream of Beipanjiang River. The total installed capacity of the engineering design is 180MW. The normal high water level is 1450m. Total storage capacity is 2.793 × 108m3. The retaining works

22、are parabolic double RCC double-curvature arch dams. The altitudes of RCC arch dam crest and dam base are 1452.50m a</p><p>　　Combining with the technical requirements and features， this paper summarizes the

23、 fiber layout principle through repeated site experiments and explorations. Considering the features and monitored objectives of DFTS， the optical fiber of Wanjiakouzi high RCC arch dam is arranged in the 4# dam of crown

24、 cantilever and 6# dam section of riverbed. The arrangement direction almost parallels to the dam facings of upstream and downstream. The border of optical fiber is 3m away from transverse joint and </p><p>

25、　　Fig. 1. The collocation diagram of DTS sensing net in typical section </p><p>　　During the construction of RCC， there are so many transport machineries， rolling equipment， pipelines and the work is extensi

26、ve， while the fiber material is fine， sensitive and easy to break. There is a huge divergence between them. Therefore， the research on laying technology of optical fiber is particularly important. Achieving 100% survival

27、 rate of optical fiber needs careful experiments and site studies to its laying technology. This is the key point to achieve project successfully. Accordin</p><p>　　4. Monitoring Results and Analysis </p&

28、gt;<p>　　The atmospheric environment temperature and water temperature of 4# dam were measured with conventional thermometer and DTS from April 4 to September 20 and analyzed comparatively. It is can be seen that

29、the results are almost same and the error is less than 0.3 ℃， which fully demonstrates the accuracy and reliability of DTS measurement results. </p><p>　　This paper selects the actual temperature measurement

30、 processes of certain specific altitudes from confined region of strong foundation， confined region of weak foundation and non-confined region to research heat of hydration of RCC dam. Generally， it is agreed that confin

31、ed region of strong foundation takes 0.1 to 0.2 times of long side of base plate and the confined region of weak foundation takes 0.2 to 0.4 times of long side of base plate. The one which takes more than 0.4 times of lo

32、ng side</p><p>　　Fig. 2. The temperature process curve of 4# dam body’s feature points at 1289.5m， 1298m， 1315m altitude. </p><p>　　Figure 2 is the temperature process curve at 1289.5， 1298， 131

33、5m altitude， it shows the process time of temperature rise is 14 days， mainly due to the impacts of the residual heat of hydration and adiabatic temperature rise， then relatively stable and it varied with the air tempera

34、ture change. It is easy to see that the temperature process curve meets the skewed normal distribution through the analysis of the temperature process curve of concrete’s feature points at every altitude. There is obvi&l

35、t;/p><p>　　In order to compare the effect of cooling pipes on temperature， the most typical points D and E at 1298m altitude were taken， in which both of them were at same altitude and third RCC area. The diffe

36、rence in horizontal distance between them was 12m. Points D and E were in the location of 3m away from the transverse joint of 4# dam， in which point E was 1m away from dam downstream. Here， there was a main cooling pipe

37、. The distance between the pipe and point E was 2m， while the distance with point</p><p>　　References </p><p>　　1.Yangbo Li & Dahai Huang & Jianshu Ouyang. Comparative Experiment Researc

38、h on Optical Fiber Temperature Measurement and Conventional Temperature Measurement of Concrete. Journal of Hydroelectric Engineering， 3， 2010 </p><p>　　2. Duquan Li & Baojun Zhao & Li Zhang. Applica

39、tion Research of DTS Technology in the Concrete Temperature Monitoring of Lawaxi Arch Dam. Northwest Hydropower， 3， 2009 </p><p>　　3.Zaixuan Zhang & Shangzhong Jin & Jianfeng Wang etc. Research Devel

40、opment of Distributed Fiber-optic Roman Photon Temperature Sensor. Chinese Journal of Lasers， 11， 2010 </p><p>　　4.Desuo Cai. The Application of Optical Fiber Sensing Technology in Dam Engineering in 2010. C