## 3 Test Method: 3D Laser Scanning  
The collapsed samples were collected after uniaxial compression test. The roughness of the failure surface is different with the ground type mixed with concrete. If the soil particles size is large, the failure can occur at the boundary between the grouting and the soil. The shape of the failure surface is affected by the soil type and hence the failure surface was scanned to determine the roughness of the failure surface in three types of pile samples. The collapsed samples are grouting samples, mixed samples of grouting and gravel (100%), and mixed samples of grouting and sand (100%) (see Figure 2). The technologies to simulate the three-dimensional shape of a structure are limited, such as a three-dimensional camera or three-dimensional laser scanning. The three-dimensional laser scanning has higher resolution and accuracy than other methods. Therefore, in order to measure local curvature such as roughness, 3D laser scanning with high resolution should be used. As shown in Figure 3a, the laser scanner can shoot lasers by rotating a laser head in the vertical and transverse directions and then collects reflected lasers from the object. The reflected point is expressed in three-dimensional coordinates by calculating the x, y, z positions of each point using the speed of the laser, the time of the reflected laser, and the angle of the laser scanner in the vertical and transverse directions. It is necessary to understand the local shape change of the failure surface to  
Figure 1: Soil collapsing effect in CFA pile. Figure 2: Test samples for surface roughness analysis. define the roughness. Especially, there are many areas affected by partial shadowing due to the gravel protrusion in the gravel sample and hence scanning was performed at three locations: center of the sample, and 45\({}^{\circ}\) away from the center (see Figure 2(b)). The laser scanning was performed by using TOPCON gls 2000 scanner as shown in Figure 2(c). The resolution of the scanner was set as 3.1 mm when the distance between the scanner and the object is 10 m. The distance between the scanner and the pile samples was about 1 m so that the actual resolution is approximately 0.3 mm. Two scans were performed at the same location to increase resolution and accuracy. Since six laser scans were performed in total, it is expected to have six times higher resolution than the set resolution. The local coordinates of each scanning data can be changed by the different scanning locations. Target scanning was performed with three reference targets to merge different scanned point clouds into a same coordinate system, as shown in Figure 2(d). Tilting of scanner was checked after the completion of the scanning to determine if there was movement of the laser scanner. There were angle changes before and after scanning which can be considered a negligible movement. Figure 4 shows schematic diagrams of the expected point clouds of each sample at different scanning locations. Gravel sample is expected to have more shadowed effects. The overall roughness can be expressed by merging the point clouds collected at the front and sides due to the protrusion of gravels from the failure surface (see Figure 3(a)). Therefore, scanning at various angles is essential in gravel samples in order to evaluate the roughness appropriately. In the grouting sample, the resolution of point cloud of failure surface can be different depending on the scanning location. However, if there is a section in which  
Figure 3: Scanning of three samples. the angle of the failure surface is changed sharply, this section can be expressed in more detail with multiple scanning at different locations (see Figure 3(b)). The grain size of sand is about 1 mm. Since the resolution of the laser scanning used in this paper is 0.3 mm and six scans were performed, the roughness caused by the sand grain can be detected on the failure surface of the sand sample.