## 5 Engineering Application  
The PBG gravel soil earth core wall rockfill dam with a maximum height of 186 m was completed and stored in water for power generation in 2009. Its internal vertical displacement was monitored by the hydraulic overflow settlement gauge, and the measuring points of the typical profile (profile 0 + 240 m) were arranged, as shown in Figure 11. Due to the impact of temporary dam top removal and permanent dam top construction in 2012, there were many missing measurements between 2012 and 2013. Since completing the automation transformation in August 2013, the continuity of measured values was good. However, there were still some phenomena such as unstable measured values at some measuring points and blockage of instrument pipelines. For example, the CH10 and CH13 at the elevation of 725 m were damaged and measuring stopped in 2015. The stability of the CH14 measured value was poor, with an anomalous steep step from July 2013 to July 2014. At present, the measured value is close to the measuring range of the instrument, and the reliability of the measured value is poor, as shown in Figure 12.  
To control the overall distribution characteristics of vertical displacement at profile 0 + 240 m, the original monitoring data of all measuring points are used to draw an isoline map of settlement deformation at a typical high water level moment (12 October 2017), as shown in Figure 13a. It could be seen from the figure that the settlement deformation of the profile showed an increasing downward trend from the middle of the dam body, and the maximum settlement deformation occurred above the dam foundation. It was inconsistent with the law that the maximum settlement deformation of gravel soil core wall  
Figure 11: Layout of the hydraulic overflow settlement gauge at profile 0 + 240 m.  
rockfill dam generally occurs in the area of 1/3\(\sim\)2/3 dam height. Analysis of the reasons should be related to the lack of measuring points at 731 m elevation and the unreliable measurement of CH14. To avoid misjuddment of dam operation behavior, a VIP-cokriging two-dimensional spatial model of internal vertical displacement at profile 0 + 240 m was constructed in this paper. The model was used to supplement the missing measured values of CH10 and CH13, and to repair the measured values of CH14. By analyzing the variable importance for projection, as shown in Figure 14, the cokriging spatial model is constructed by selecting aging and water pressure as covariates. To further verify the accuracy and stability of the model, cross-validation was carried out by selecting the moments when all measurement points were intact. Except for the points CH8 and CH16, the relative errors of the remaining measurement points ranged from 0.24% to 1.90%, especially the relative errors of CH10, CH13, and CH14 measurement points were minor and controlled within 2%; the calculation results are shown in Figure 15 and Table 4. The reasons for it should be related to the fact that the points CH13 and CH14 were internal measuring points and that the CH10 point was close to the known measuring points and had more known measuring points around it. Therefore, it was feasible to use the VIP-cokriging spatial model to repair the data of measuring points. Figure 12: Duration hydrograph of the hydraulic overflow settlement gauge at 725 m elevation at profile 0 + 240 m.  
Figure 14: Results of the variable importance for projection of horizontal deformation at profile 0 + 240 m.  
Figure 13: Isoline map of the internal settlement deformation of the dam at profile 0 + 240 m (12 October 2017). The duration hydrograph of the repaired measuring points is shown in Figure 12, and the isoline map of the vertical displacement of the profile is shown in Figure 13b. The pattern of changes in the measured values of the repaired points was the same as that before 2012, with an overall convergence and stabilization and a high degree of restoration accuracy.