## 2 Field Experimental Program
### Layout of Cooling Pipes and Thermometers  
The cooling pipes of the two dams were arranged in the same way, with each main pipe connected to two or three branches outside the dam, and the branch pipe was arranged in a serpentine shape, as shown in Figure 1a. The length of each branch pipe was similar and not more than 300 m, and the layouts were mainly 1.5 m (vertical) \(\times\) 1.5 m (horizontal). This paper only investigates this situation. The cooling pipes were buried in concrete pouring layers, as shown in Figure 1b. The water flow rate and temperature of each main pipe were monitored, but the data concerning each branch pipe were not collected. Figure 1 shows the locations of four point-thermometers (T1-T4) used to monitor the temperature of the concrete in the middle of the two layers of cooling pipes, with different thermometers corresponding to different branches. A digital temperature sensor (DS18B20) was used for each point-thermometer with an accuracy of \(\pm\)0.3 \({}^{\circ}\)C. Data were uploaded to the database automatically with an acquisition frequency of 3 hours.  
A dense array of platinum resistance thermometers (PT1000) with a precision of \(\pm\)0.1 \({}^{\circ}\)C was designed to explore the influence of the heat exchange between the concrete boundary and the external environment on the internal temperature. Data were uploaded to the database automatically with an acquisition frequency of 5 min. Figure 2a illustrates the arrangement of the five sensors in a string  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Dam**} & **Cement** & **Water** & **Fly Ash** & **Fine Aggregates** & **Coarse Aggregates** \\  & \(\left(\mathbf{kg}/\mathbf{m}^{3}\right)\) & \(\left(\mathbf{kg}/\mathbf{m}^{3}\right)\) & \(\left(\mathbf{kg}/\mathbf{m}^{3}\right)\) & \(\left(\mathbf{kg}/\mathbf{m}^{3}\right)\) \\ \hline Baihetan & 120 & 85 & 65 & 535 & 1695 \\ Wudongde & 108 & 83 & 58 & 574 & 1740 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Mixing proportions of the concrete.  
Figure 1: Embedded positions of thermometers and cooling pipes: (**a**) layout of thermometers and branch pipes; (**b**) vertical distribution of thermometers and main pipes.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Cooling Pipe**} & **Inner Diameter** & **Wall Thickness** & **Outer Diameter** \\  & **(mm)** & **(mm)** & **(mm)** \\ \hline Main pipe & 32.6 & 3.7 & 40 \\ Branch pipe & 28 & 2 & 32 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Specifications of the cooling pipes.  
of thermometers, with each thermometer placed in the precast concrete column according to the arrangement shown in Figure 2b. Three groups of thermometer strings (G1-G3), as mentioned above, were used to test the temperature distribution near the surface, interior, and bottom of the concrete. The buried positions of each thermometer string are shown in Figure 1. Thermometer string G1 was located at the bottom of the concrete pouring block, in which the first thermometer was placed on the bottom, and the last thermometer was close to the first layer of the cooling pipe. Thermometer string G2 was located in the fifth pouring layer, in which the first thermometer was close to the second layer of the cooling pipe. Thermometer string G3 was located in the ninth pouring layer, in which the first thermometer was 5 cm away from the surface of the concrete pouring block.