## 3 Parameter Identification
### Strength  
The soil samples were taken from different locations of the landslide area. Figure 7 shows the locations of soil samples D and G2 around the main scarp and soil samples G1 and MG at the toe projected into the cross section. Note that the samples were not taken directly in the line of the cross section but laterally from it [51], which took into account the impact of heterogeneous characteristics of the glacial deposits on the mechanical behaviour. Consolidated drained triaxial tests (CD) were conducted and the resulting Mohr-Coulomb parameters are shown in Table 1. Soil samples G1 and G2 were glacial deposits from the uppermost layer. Sample D was also from the upper layer; however, the material was debris flow deposit, which represented only a small percentage of the soil in the upper layer. Sample M was marl from the Gosau Group exposed at the right later flank of the landslide [51]. Soil sample MG was taken at the boundary of glacial deposits and marl, representing a mixture of both. In the consolidated drained triaxial tests, the lateral pressure (\(\sigma_{3}\)) was kept at 300 kPa, 600 kPa, and 900 kPa; see Figure 8.  
Figure 7: Simplified models of the slope (modified from Krenn [51] and Renner [53]). (**a**) Prefailure geometry of the Ludoialm landslide; (**b**) postfailure geometry of the Ludoialm landslide and locations of soil samples projected into the cross section of Figure 6. Note that the samples were not taken directly in the line of the cross section but laterally from it. It can be concluded from Table 1 that marl had a higher cohesion than glacial deposit. The strengths of the glacial deposits taken from different locations varied widely. The particle size distribution tests were performed at the laboratories of the University of Natural Resources and Life Sciences in Vienna (BOKU) and the University of Innsbruck (UIBK). The particle size was classified according to ONORM L 1061-1 [55] and ONORM L 1061-2 [56], and the percentages of each grain size class (clay, silt, sand, and gravel) are shown in Table 2. The content of clay and silt for the glacial deposits usually exceeded 50%. The fraction of clay plus silt of sample D, i.e., debris flow deposits, was very low, about half as much as in the glacial deposit samples, while the content of gravel was very high, which well explains the high friction angle of this sample. To summarize all these characteristics, the soil sample D embodied very different characteristics from other ones also taken from the uppermost layer and constituted only a small portion of the upper layer. This sample was therefore not taken into account in the computation. Since sample MG was taken from the boundary of glacial deposit and marl, its cohesion was expected to be higher than the samples of pure glacial deposits. However, it was heavily weathered and its strength was closer to that of the upper layer, so it was taken into account in the determination of the strength for the upper layer. The cohesion of G2 was remarkably lower than expected for glacial deposits, which may be due to the fact that it was taken near the main scrap of the slope. We took a computational mixture of the soil samples to represent the strength parameters of the upper layer, i.e., the sliding mass. The parameter combination of MG, G1, and G2 was used for the upper layer. Based on the linear fitting method and under consideration of all stress levels [57; 58], the peak shear strength parameters of the Mohr-Coulomb failure criterion were computed from the results of triaxial experiments, as listed in Table 3 and shown in Figure 8. As for the marl layer, only one sample was available, and its values were used in the computation.