## 4 Engineering Application  
### Discontinuity Set Survey in a Gold Mine  
A gold mine is located in Shandong province, China, with a mining depth exceeding one kilometer underground. The structural planes such as joints and fissures in this mine area are quite developed (Figure 3), which seriously threatens the stability of roadways and stopes. Hence, investigating the scale, occurrence, and distribution of the structural planes in this mine is crucial for the failure mode analysis and stability evaluation of the surrounding rock. A 3D non-contact measuring system (ShapeMetriX 3D) for the geometric parameters of the rock mass is used to investigate the rock mass structural planes of the mine, which primarily contains a high-resolution standard DSLR zoom camera (Nikon Imaging Japan Inc., Tokyo, Japan), corresponding marker rod components, and a 3D visual analysis software system, as shown in Figure 4. This system can provide real 3D images of the rock mass surface and determine the geometric measurement data of the rock discontinuity sets by being combined with the matching image analysis software, thus recording the tunnel outline and the spatial position of the rock mass discontinuity. The system essentially relies on the digital image correlation technique, which organizes the digital information of the rock mass to obtain information on the rock mass structure plane occurrence. Figure 5 shows the basic principle of the 3D non-contact photogrammetry. Firstly, the investigation area is determined, and the left and right views of the exposure surface are obtained through the calibrated high-pixel camera, such as the points P\({}_{1}\)(\(u\), \(v\)) and P\({}_{2}\)(\(u\), \(v\)). Afterwards, the two views in the picture are imported into a software analysis system, and the system automatically identifies the points P\({}_{1}\)(\(u\), \(v\)) and P\({}_{2}\)(\(u\), \(v\)) and reconstructs them in three dimensions to obtain 3D points P(\(x\), \(y\), \(z\)) based on a series of techniques such as pixel point matching and image distortion deviation correction. Finally, the 3D model is synthesized and the direction and distance are realistic to obtain a true 3D digital model of the rock mass surface. According to the reconstructed 3D surface, the discontinuity sets of rock masses can be marked, such as the joint trace length, spacing, and fault distance, and thus, the geometric occurrence information of structural planes can be statistically analyzed. The structural planes of the rock masses are investigated at multiple depth levels in the gold mine by using the ShapeMetriX 3D system. The following is an example of measuring the structural planes at a measuring point at a depth of 765 m underground. The left and right views of the survey location are identified (Figure 6a). These two views are imported into the ShapeMetriX 3D software analysis system, the key measurement  
Figure 4: ShapeMetriX 3D measurement system. Figure 5: Imaging principle of the 3D surface measurement [9]. Figure 3: Illustrations of the geographical location and structural plane development of the gold mine. areas are delineated, the 3D models are synthesized, and the direction and distance are realistically transformed to obtain the 3D view of the rock mass surface (Figure 6b). On the synthesized 3D map, rock joints are grouped according to the distribution of the main joints and fractures, and different colors represent different groups. There are two groups of the main joint distribution, namely, the red group and the blue group in Figure 6c. Based on the spatial distribution and grouping of discontinuity sets, the stereographic projection map (Figure 6d) and the structural plane trace distribution map (Figure 6e), which can reflect the joint spacing, are drawn. The spatial distribution of rock discontinuity sets can be described by spatial geometric parameters such as occurrence, shape, scale, and spacing, and these basic geometrical features can be used to determine the spatial shape characteristics of each group of rock mass discontinuities.