1 For the given failure surface , determine the factor of safety in terms of total stress for the slope detailed in Figure 1 . The unit weight for both soils is 19 kN/m 3 . The characteristic undrained strength ( c u ) is 30 kN/m 2 for soil 1 and 45 kN/m 2 for soil 2. What is the factor of safety if allowance is made for the development of a tension crack? Figure 1