(Solved): 1. Consider the seepage beneath an earth dam shown in Figure 1 below. The underlyine. permeable soi ...

1. Consider the seepage beneath an earth dam shown in Figure 1 below. The underlyine. permeable soil is homogeneous, isotropic, and fully saturated with water. The soil extends to the impermeable barrier D-E-F-G. The water depth in the dam is $15\mathrm{m}$; no water accumulates downstream of the dam. A horizontal blanket drain on the downstream side of the dam acts as if it is infinitely permeable, i.e, there is no hydraulic gradient along it. a) A larger version of Fig. 1 is provided on supplementary sheet $\$1$ at the back of this exam paper. Construct a quantitatively accurate flow net, with $n_m=4.5$ flow tubes, on it. Indicate numerical values for each equipotential line and the direction of flow, taking the datum to be the level of the drain. Hint: - The flow net should have 6 equipotential lines, of which one passes through point $A$. - Assume thot the flow in the unsaturated soil is negligible and that the woter toble is a free surface. [14 marks] Be sure to attach the sheet to your exam script prior to submission. b) Assume that the hydraulic conductivity of the underlying saturated soil is $1\times 10^5\mathrm{m}/\mathrm{s}$. Evaluate the seepage loss through the earth dam. [2 marks] c) Calculate the pore pressure at point A. For simplicity, take gravitational acceleration to be $10\mathrm{m}/{\mathrm{s}}^2$ and water density to be $1000\mathrm{kg}/{\mathrm{m}}^2$. [4 marks]