## 2 Application of Borehole Camera Technology in Engineering
### Boreholes and Image Characteristics of Wudongde Hydropower Station  
Wudongde Hydropower Station is the uppermost one of the four hydroelectric escalators (Wudongde, Baihetan, Xiluodu, and Xiangjiaba) planned and constructed in the lower reaches of the Jinsha River. The right bank of the river section where the dam site is located is in Luquan County, Kunming City, Yunnan Province, China, and the left bank belongs to Huidong County, Sichuan Province. The designed water storage level is 975 m, and the total storage capacity is 5.863 billion m\({}^{3}\). The dam is a concrete double-curved arch dam with a maximum height of 265 m. The power station is an underground powerhouse, with six 725 MW units on each side. The total installed capacity is 8700 MW, and the average power generation over many years has been 39.46 billion kw/h. The Wudongde Hydropower Station is a Class I project in China. The pivot project consists of dams, flood discharge and energy dissipation buildings, and water diversion and power generation systems. The borehole camera system is mainly used to divide the lithology of the important boreholes in the dam site, determine the geological structure, determine the presence of any weak layers, and divide the rock mass unloading zone after conducting the borehole hydrogeological survey [33; 34; 35]. It is also used to establish the bedrock occurrence, slip zone and overburden properties of the key parts of the Jinpingzi landslide, providing a reliable basis for the geological department to demonstrate the stability status and deformation development trend of the landslide. The schematic diagram of dam body structure is shown in Figure 2.  
The panoramic borehole images of eight important parts of the dam site area and the Jinpingzi landslide area of the hydropower station demonstrate that the DPBCS can obtain real-time video images of the rock structure in the borehole wall. Furthermore, the obtained panoramic borehole images can accurately record the structural characteristics of the rock mass in the borehole and provide a construction basis for engineers. Therefore, the analysis and extraction of the rock mass structure parameters obtained from the borehole  
Figure 1: Panoramic borehole camera probes. image are valuable final data outcomes. Therefore, the next step is to analyze and study the borehole image record data of the Wudongde Hydropower Station. A panoramic borehole image is an indirect reflection of the rock mass structure of the borehole wall. It is the image resulting from the illuminated rock mass structure being reflected in the conical mirror of the panoramic camera probe. Therefore, the rock mass structure of the hole wall determines the color depth composition of the drilling image. Due to the poor reflectivity of cracks, fracture planes, holes, broken zones and other areas, such features appear dark in the borehole image, as shown in Figure 3.  
Figure 3a is of hole number DJ1, from a panoramic borehole image taken at a depth of about 0.3-2.3 m as an example; Figure 3b is of hole number DJ4, from a panoramic borehole image taken at a depth of about 30-32 m as an example. The structural planes in a panoramic borehole image are similar to sine curves after unfolding. The standard structure surface in an ideal state is a standard sine curve distributed in the horizontal plane after being expanded [12]. The structure plane in a non-ideal state is also an approximate sine curve in the expanded image of the panoramic borehole image, as is shown in Figure 3 The characteristics of the structural plane are mainly manifested in the difference in the position, dip direction, dip, and gap width of the structural plane, which, when represented as a sine curve, is the difference in position, amplitude, phase, and line width of the curve.