Ultimate Limit State ULS

Bearing capacity and slope stability analysis may be carried out using a complex plasticity based model (Clarke et al., 2008) that requires many parameters, or a simple Mohr -Coulomb failure criterion (e.g. Nater et al., 2008). Similar to the SLS state, it is important that the soil parameters are determined in the laboratory for the ground and loading conditions found in the field. Because ground temperatures will change in the future, ultimate limit state analyses are not limited to one particular point in time, but require transient analysis, resulting in predictions of the evolution of the safety factor with time. In order to account for all uncertainties involved when designing for long-term ULS in permafrost, it is suggested that the desired safety factor is increased by 25%, as an initial approximation. However, this change may have to be adjusted for different projects, elements and quality of climate parameters available.

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