An infinite slope shown in Figure Q5 below is inclined at a gradient of 1V:2H and with soil properties of y = y sat = 18 kN/m, c' = 0 kPa and '= 32. A hard layer is found at 4m depth with groundwater table at 0.5m above this hard stratum. Failure surface is assumed to occur at the interface of the hard layer and top soil. a. Find the overdesign factor (ODF) using EC7 DA1C1 and DA1C2. b. After prolonged heavy rainfall, the slope failed. Find the depth of groundwater when failure occurred? Am 2H Y = Ysat = 18 kN/m c' = 0 kPa $' = 32 Hard stratum parallel flow 1V GWT Figure Q5 0.5m c. At dry season, the water table is found to be located below the potential slip plane. Due to capillary action, matric suction (Ua-Uw) of 20 kPa is developed within the top 4m soil. Assuming that b = 15, calculate the total cohesion of the top soil. Find the ODF of the slope using DA1C2 by taking into account of the effect of matric suction during dry season?