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5. (a) For the existing retaining wall as shown below, assume the wall is retaining material that has a shear strength of c'= 0 and '= 36°, with ys = 19 kN/m”; the friction angle along the retaining wall base = 0.90'; groundwater level is 20m below the ground surface behind the wall. Use the approach recommended in the First Edition of Geoguide 1. State clearly other assumptions as necessary for the calculation. (17 marks) 10kN/m2 HA 1.5m 30kN/m 3m 0.5m 2m Note: e = B 2 M.-M. N where Mis the restoring moment M, is the overturning moment N is the reaction force B is wall base width, and e is eccentricity of the point of action of the reaction force on the wall base (i) What are the stresses acting on the wall? (5 marks) (ii) What is the factor of safety against sliding failure of the above retaining wall? (5 marks) (iii) What is the factor of safety against overturning failure of the above retaining wall? (5 marks) (iv) Would tension develop along the base of above retaining wall? (2 marks) (b) If the groundwater table in (a) above is 1m below ground (active side) instead, discuss how would this affect your answers in (i) to (iv) above. (3 marks) Page 4 of 8