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4.5 Limitations of limit equilibrium methods Wright, Kulhawy, & Duncan (1973) state that limit equilibrium methods are ââ¦subject to criticism on theoretical groundsâ since assumptions are employed that result in the normal stress calculated using only conditions of static equilibrium, without consideration of the stress-strain characteristics of the soil. The GEO-SLOPE SLOPE/W Stability Modelling (2008) document states that ââ¦this has two consequences, one is that local variations in safety factors cannot be considered, the other is that the calculated stress distributions are often unrealisticâ. To overcome this issue, stresses can be found using the upper and lower bound theorem methods, or by finite element analysis then incorporated in the stability analysis to compute a factor of safety. Alternatively, the factor of safety can be analysed using probabilistic analyses to account for local variations in soil properties. Wright, Kulhawy & Duncan (1973) also state that most limit equilibrium methods assume that the factor of safety for each slice is the same however this would only be true at failure when each slice has a factor of safety of one. 4.6 Computer modelling 4.6.1 GeoStudioâ¢ SLOPE/W GeoStudioâ¢ SLOPE/W (2012) is a computer modelling program which uses limit equilibrium methods to determine a factor of safety of soil embankments. SLOPE/W was used for the deterministic analyses to calculate factors of safety and also used for the probabilistic analysis to determine the probability of failure using Monte Carlo simulations. The GEO-SLOPE Slope Modelling (2008) document states ââ¦the SLOPE/W results must always be judged in context of what can exist in realityâ. 4.6.2 Microsoft Excelâ¢ Microsoft Excelâ¢ spreadsheets can be used for simple limit equilibrium methods to obtain factors of safety. Spreadsheets have been developed by the author for Bishopâs simplified method and Felleniusâ method for undrained and drained conditions. Both methods have limitations in that the width, height, and angle of the base of each slice are unknown and need to be specified beforehand. The number of slices and iterations also has to be manually entered. The spreadsheets are not able to determine the location of the slip circle. This is a significant limitation as each potential failure surface will need to be analysed separately to determine 48