Solution HW#5 - Solution of Homework No.4 CEE 330 Fall...

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Solution of Homework No.4 – CEE 330 – Fall 2009-10 Date: November 5, 2009 Problem 1: A retention pond is to be constructed on a natural loose silty sand (SM) soil. The natural water table is at a depth of 20m below the bottom of the pond. Neglecting evaporation, rainfall, and additional runoff into the pond, calculated how long it will take for the pond to drain from a filled water depth of 3m to a water depth of 0.5m. Consider two cases: (i) A 2m thick recompacted dense silty sand (SM) liner. Recompaction of the natural silty sands to a dense state will result in a coefficient of permeability of 1x10 -5 m/s. ln(P 0 /P)=(Ak)/(aL) · t for our case A=a: ln(P 0 /P)=k/L · t t = ln(P 0 /P) · L/k P 0 = 30kPa P = 5kPa k=1x10 -5 m/s t = 3.6x10 5 sec = 4.2 days = 0.01 years (ii) The pond is lined with a 1m thick compacted high plasticity clay liner (CH) with a coefficient of permeability of 3x10 -9 m/s. ln(P 0 /P)=(Ak)/(aL) · t for our case A=a: ln(P 0 /P)=k/L · t t = ln(P 0 /P) · L/k P 0 = 30kPa P = 5kPa k=3x10 -9 m/s t = 6x10 8 sec = 6913 days = 18.9 years Express answers in days and years. Which liner would you recommend? The problem described is a retention pond. It is desirable to retain the water as long as possible. We would choose the 1m thick compacted high plasticity clay liner. If we would like to retain the water for more than 19 years we could increase the thickness of the liner (or add a geosynthetic layer).
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Solution HW#5 - Solution of Homework No.4 CEE 330 Fall...

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