# Monitoring and Data Analysis in Small-Scale Landslide Physical Model
## 4 Results
### High-Speed Cameras

Table 9: Duration and frequency of filming by high-speed cameras used in tests. be assigned due to the elements of the platform that cover them, such as constraints of plexiglass sides and tensioned wire stretched over the model. Observed points are linked by lines in a longitudinal profile made of points from the second row (Figure 9). Connecting the points in lines allows for easier follow-up in the next stages of the test. This profile is one of the best examples because almost all points from the second row are visible in the undeformed reference stage (Stage 1) shown in Figure 9. Point 2,1 was not recorded by the left camera, and point 2,7 was not visible due to the tensioned wire placed just above the point in the lower part of the model as a protection from buckling of the plexiglass sides. Changes of \(x,y,\) and \(z\) coordinates, i.e., displacements, are measured by comparison with the position of the recognized reference points through consecutive images that correspond to different degrees of deformation (stages through time). Since the whole test was recorded in the sequence of 479 images, a few characteristic stages of the recorded test were chosen and presented for the visible points. Besides the initial stage (Stage 1), two other stages were chosen because of the visibility of points and the biggest displacements happening around that time--stage 330 and stage 434. Figure 8: Points of the longitudinal profile [66]. Figure 9: 3D view of the reference undeformed image—Stage 1 [66]. undeformed image from stage 1 to stage 330 visible in Figure 10 which was recorded at the moment of formation of the crack at the bottom of the middle part of the model, on the edge of the point 13. Here, all points before number 13 are lost in the sliding of the mass or covered by the water level that formed at the foot of the slope. Further, points 15 and 16 are not visible above, probably due to the poor lighting and creation of a shadow above the aforementioned points. At the top of the model, on the horizontal part of the line, point 23 cannot be defined. The possible reason could be the reduced visibility of the point by retaining water droplets on it and/or the position of the point being too close to the plexiglass. In Stage 434 (Figure 11), other points above the point 13 are lost in the sliding of the material and separation of the inclined part of the slope from the upper horizontal part of the slope. However, here, by comparing the values of \(x\), \(y\), and \(z\) coordinates of the few visible points such as 19, 20, and 21, the subsidence of material is noticeable in those points due to the formation of cracks inside the landslide body. By further retrogressive movement of the slope, the marker points slide along with the material, and the system cannot recognize points covered by the material or submerged in water; therefore, the visibility of an increasing number of points decreases through stages of the test. Figure 11: 3D view of the analyzed stages of the longitudinal profile—Stage 434 [66]. Figure 10: 3D view of the analyzed stages of the longitudinal profile—Stage 330 [66]. The changes in the longitudinal profile during the test can be graphically presented as in Figure 12. It can be possible to monitor the movements of the observed marker points along the profile and compare the stages with the soil moisture contents. For example, Stage 330 (Figure 10) is immediately after the landslide initiation when the constant VWCs were reached at all sensor depths, landslide development was retrogressively developed, and the disturbance in the middle part of the slope at the shallowest sensor at the depth of 6 cm was identified. In Figure 12b (Stage 360), points 15 and 16 are lost probably due to the poor lighting or shadow fell at the points, while in Figure 12c, only the upper part of the profile is visible as the material of the slope just subsided and has not flow downward yet.