A prestressed concrete pipe of 0.5 m diameter is driven in medium dense sand up to 10 m depth. The groundwater table level is at 3 m depth below the surface. The properties of the sand are: Angle of internal friction of sand, o' Angle of wall friction between pile and sand, 8 Post-driving horizontal earth pressure co-efficient Saturated unit weight of sand Unit weight of sand above groundwater table 30 degrees 20 degrees 1 19 kN/m 17 kN/m If the unit shaft resistance reaches a limiting value at 15 D, where D is the diameter of the pile, estimate the skin friction resistance of the pile.