# Geotechnical Study of Raspadalica Cliff Rockfall, Croatia
## 4 Results
### Results of the Geological and Geotechnical Survey
Although some developed remote sensing methods that have been successfully applied to identify other discontinuity features (separation, infilling, discontinuity wall roughness, and weathering grade) [83; 86; 93; 94; 95; 96; 97] were used in the remote sensing survey of the Raspadalica Cliff, it was found that the resulting data had too much scatter and were not as reliable as the data obtained by in situ traditional geological and geotechnical surveys. Based on the statistical analyses of the data obtained from the 3D HRPC model of Raspadalica Cliff using the _Cloud Compare_ software, the mean values of the orientations, discontinuity sets spacing and persistence for the total area of the Raspadalica Cliff are presented in Table 2. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Joint Set** & **Dip Direction/Dip** & **Discontinuity Spacing (cm)** & **Persistence (m)** \\ \hline Joint Set 1 & 8–209/73–84 & 250–500 & \textgreater{}20 \\ Joint Set 2 & 88–281/76–88 & 120–310 & \textgreater{}20 \\ Bedding & 224–307/1–23 & 10–150 & \textgreater{}20 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Values of orientations, discontinuity set spacing, and persistence obtained by remote sensing survey and analysis. Figure 9: Three-dimensional HR Point Cloud of the Raspadalica Cliff with extracted facets using the _Cloud Compare Facet_ plugin [43; 61] (Fast Marching procedure). Orange and red to cyan facets represent Joint Set 1, parallel with the cliff face; green to yellow facets represent Joint Set 2, almost orthogonal to Joint Set 1; and blue facets represent Joint Set 3 (bedding). Compared to the results obtained by traditional geological and geotechnical surveys, the remote sensing and data analysis results yielded only slightly different mean discontinuity dip directions and dip values for identically determined joint sets. These discrepancies are caused by a significantly higher number of statistically analyzed data obtained by the remote sensing survey of the entire cliff face, while the traditional geological and geotechnical surveys were limited to the accessible zone at the foot of the cliff and the low number of joint measurements. Moreover, the block volumes were visually estimated in the traditional geological and geotechnical survey, while the dimensions of the blocks were relatively precisely measured using the tools available in the _Cloud Compare_ software [92]. Another important element in determining the relevant block volume is discontinuity persistence. The discontinuity size and persistence at the Raspadalica Cliff were derived from the measured length of the traces on the exposed cliff face using manual methods (scanline sampling and window sampling) in combination with various automatic and semi-automatic image analysis techniques applied to the 3D HRPC model. As long as the rock face is clearly exposed, manual sampling is a common method for discontinuity persistence determination [89]. Although the straight scanlines imply a direct measurement of the joint traces between the joint intersections on the rock slope face, in this research, most of the data were provided by measurements from the 3D HRPC model using the _Cloud Compare Distances_ tool. Direct surveys were conducted at the easily accessible foot of the cliff, where detailed scanline surveys were completed [98]. Window sampling was also used for discontinuity persistence determination. Rectangular areas were selected for window sampling because of the perpendicular shape of the blocks, and the side lengths of the rectangles were twice as long as the sides of the largest blocks. The results of the manual methods were combined with the results of automatic and semi-automatic image analysis techniques [22; 47; 62; 73; 76; 77; 80; 84; 85] applied to the 3D HRPC model and used to determine the size of the relevant block.