NCEES 2011 Sample Questions Problem 116-Assistance Needed

Problem concerns a retaining wall; all variables are given; neglect wall friction and using Rankine active pressure theory find the factor of safeety against overturning at the toe of the wall.

Find Ka, Pa, Ma and this solution makes sense until determining the total resisting moment. The issue is determining the location and eccentricity of the vertical force component.

Thanks for your help.

Triangular weight component (area = 8 sf, weight = 1200 lb/ft, eccentricity = 2/3 x 2 = 1.33 ft, moment = 1600 lb-ft/ft). This is wrong in the solution. It is missing the 2 ft. The diagram has the centroid location dimensioned as 2/3 Should be 2/3 x 2 = 4/3

Rectangular weight component (area = 16 sf, weight = 2400 lb/ft, eccentricity = 3 ft, moment = 7200 lb-ft/ft)

Total stabilizing moment about the toe = 8800 lb-ft/ft

FS = 8800/2883 = 3.05

ncees has issued an errata for this question, its on their website

I suspected an error in the solution but was unable to find the errata on this. Thanks for your quick assistance.

Thanks! Had the exact same question.