Question

Draw a flow netlfor the case of a long concrete dam shown in the Figure below and calculate the quantity of seepage underneath the dam. The soil underneath the dam is homogeneous and isotropic with a coefficient of permeability of 1.8 x 106 m/s. Determine the minimum weight of the dam required to maintain a factor of safety of 1.5 against the uplift of the dam. If the saturated unit weight of the soil is 18 KN/mP, check whether quicksand condition develops at the toe of the dam. Water Leve Toe Ground Surface 「 /X 4.5 m 6 m Bedrock

Answer 1

Given that: Coefficient of permeability = 1.8 times 10^-6 m/sec. Saturated weight of the soil T_sat = 18 KN/m^3 = 18 times 10^3 N/m^3 Factor of safety = 1.5 The distance (or) height between Ground surface and water level = 4m from Bed rack to Ground surface = 6m \r\n weight of the Dam Q = k middot H times N_f/N_D rightarrow (1) Here N_f = 4 N_D = 5 Substitute the value sin equation Q = K middot H times N_f/N_D = 1.8 times 10^-6 times 4 times 4/5 Q = 5.76 times 10^-6 m^3/sec Factor of safety f_s = i_1/1 = 4/6 f middot S = 0.666 The value of factor of safety is below the given value 1.5 so the dam construction is safe.