# Optimization Method for Improving Efficiency of Thermal Field Reconstruction in Concrete Dam
## 2 Materials and Methods
### DTS System Layout and Data Acquisition  
To meet the data requirements for reconstructing the temperature field of concrete, the optical fibers are typically laid from the upstream face to the downstream face at the construction site, aiming to cover the entire pour block [19]. Considering the cost of the DTSsystem and the complex construction environment, specific requirements for the horizontal and vertical layout of the optical fibers are proposed to ensure that the fiber laying aligns with the concrete pouring schedule. These schemes are designed considering the structural characteristics and layout requirements of different dam sections, aiming to optimize the fiber-laying effect and improve the accuracy and reliability of data collection.  
In the horizontal direction, there are three common layout schemes: \"I\" type, \"L\" type, and \"Z\" type [19]. The selection of the scheme depends on the type of concrete blocks. For dam foundation areas and gallery blocks with special structural constraints, the simple and easy-to-construct \"I\"-type scheme is recommended. Large dam blocks without special structural obstructions can achieve continuous fiber embedding using the \"L\"-type scheme. The \"Z\"-type scheme is suitable for obtaining temperature data on both sides of the transverse joints and along the axis in the middle of the dam block. To facilitate the construction and reflect the actual thermal field as much as possible, in the vertical direction, the optical fibers are arranged symmetrically between odd and even numbering of dam blocks. The optical fiber is embedded directly in the concrete, making the impact of external factors (e.g., humidity and wind) on temperature measurement accuracy negligible. Additionally, water-blocking material, inner coating plastic steel belt, and PE sheath further shield the fiber from external factors on temperature measurement accuracy.  
Figure 2 shows the DTS system layout in a concrete dam using the \"Z\"-type scheme. The optical fiber is first embedded from the upstream surface to the center of the dam block in the direction parallel to the transverse joint, then follows the direction parallel to the dam axis to the other transverse joint, and finally turns in the direction parallel to the other transverse joint to downstream surface. In this study, three digital thermometers (designated as 7#-1, 7#-2, and 7#-3) were embedded parallel to the transverse joint in the center of the concrete block, and readings were collected synchronously with the DTS system. By comparing the temperatures measured by the three digital thermometers with the temperatures of the reconstructed thermal field at the corresponding positions, the accuracy of the reconstructed thermal field can be evaluated.  
The minimum data acquisition interval of the DTS system used in this study is 10 s, allowing for continuous monitoring of the internal temperature of the concrete. The spatial and temperature resolutions of the DTS system were 1.02 m and 0.5 \({}^{\circ}\)C, respectively. By  
Figure 2: Instrumentation layout of optical fiber for thermal field reconstruction.  
setting the temperature of upstream and downstream surfaces to ambient temperature, a two-dimensional (2D) thermal field can be interpolated. Then, a three-dimensional (3D) thermal field can be constructed when combining all adjacent 2D thermal fields. As the temperature of the monitoring points keeps being updated, the real-time thermal field of the whole dam can be obtained. Since optical fiber embedding and concrete pouring occur synchronously, the thermal field digitized via interpolation algorithm analyses can concur with the construction progress.