Figure Q-2b shows a U-tube containing three soil samples whose permeabilities are ki (clean sand), k (gravelly sand) and k: (silty sand). The U-tube has a constant cross- sectional area. Also, the soil permeabilities are related such that k = 0.5k = 3k3. 10 cm 8 cm 10 cm A k B clean sand F silty sand ka E gravelly sand k D 5 cm 4 cm 6 cm 16 cm Figure Q-2b Flow across a U-tube with three soil samples. Calculate the pore (or water) pressures at points A, B, C, D, E and F. [12 marks] Hint: i. You may approach this problem by first calculating the total heads at points A, B, C, D, E and F first. Choose a suitable elevation datum. ii. Use Darcy's Law and make use of the fact that the flow velocity through all the soil samples is the same given the constant cross-sectional area.