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that values from stability charts used for short-term analysis gave quick results relevant to the stability of an embankment. Spencerâs charts produced a factor of safety of 1.5 which was 1.5% higher than Bishopâs simplified method (see Table 5.12). This was consistent with the results from Case 1, where Spencerâs method calculated a suitably similar factor of safety and the value from Bishop and Morgensternâs stability charts was an overestimate (in this case by 22%) since no pore water pressures were considered). 5.4.2 Undrained analysis Table 5.11: Case 3 factors of safety from spreadsheets and SLOPE/W for undrained conditions Fellenius Janbu simplified Morgenstern and Price Spencer General limit equilibrium 0.921 0.921 n/a n/a n/a n/a SLOPE/W 0.921 0.921 0.864 0.921 0.921 0.921 Spreadsheet 0.908 0.907 n/a n/a n/a n/a SLOPE/W 0.906 0.906 0.879 0.906 0.906 0.906 No. of slices 5 20 Method Bishop simplified Spreadsheet 0.906 Elevation (m) 15 10 5 0 0 5 10 15 20 25 30 35 40 Distance (m) Figure 5.10: Most critical slip circle in undrained SLOPE/W analysis with 20 slices Since the foundation had a greater cohesion and bulk unit weight (compared to the embankment fill), the deep-seated failure only occurred in the weaker material of the embankment, with a small section of local translational failure. The factor of safety had improved, from the situation in Case 1, by approximately 20%, indicating that the effect of a firm stratum as a foundation can improve the factor of safety. However since the failure 60