Question

The figure below shows the soil profile conditions below a 5-m deep pond. Water is seeping directly downward under steady-state conditions through the clay layer into underlying gravel. Assume the elevation datum at the top of the gravel layer and that the hydrostatic ground water table is also found in the top of the gravel and its position does not change with time or amount of flow. For these flow conditions, calculate the following: a. b. c. d. e. f. g. The pressure head and elevation head at point B (5 points). The pressure head and elevation head at point C (5 points). The pressure head and elevation head at point D (5 points). The hydraulic gradient between points B and C (5 points), The seepage rate (m3/day) for 100 m2 surface area of the pond bottom (5 points). The seepage velocity if the void ratio of the clay is 0.9 (5 points). For this problem, would the position of the equipotential lines change if the hydraulic conductivity of the clay was arbitrarily increased to 1 x 106 cm/s (5 bonus points) Pand rm Cl ay 10 m Datum7 rav

Answer 1

2 Sol": a) Poresure head at B = 5m Elevation head at B = 10 m = Total head at B, Hg = 10+5= 15m b) Elevation head at C = 5 m & : Total head at. D=0 =) Total head at 6 = He He 150 = 7.5 m so pressure head at C = 7.5-5= 2.5 m Pressure head at D=0 Elevation head at Dzo ( Datum is at D) d) Hydraulic gradient = AH = 15-7.5 = 1.5 e) ; QE KA OH = (1x167 cm x 16% mm 1x loom? x 1,5 =) Q = 105x167 m3/s = 1,5x167x(24X60x60) m3/day or Q = 0.01296 m) day + Seepage velocity Vs = 1.5x109 Q/A - 15x107/100 or Vs = 3.178 109 m/s 9). Since hydraulic gradient does not depend on Hydraulic conductivity k , so sh = ls will not change & so position of equipotential lines will not change.