Assignment: 1) A column with a soil sample has two piezometers extending from th

Question

Assignment: 1) A column with a soil sample has two piezometers extending from the top and bottom. The top piezometer has a reading 2.8 meters and the bottom has a reading of 2.3 meters. The diameter of the sand column is 30 cm, and the height (between the two piezometers) is 150 cm. a. The datum is at 0 m (at the base of the sand column), what is the total head, pressure head, elevation head at the top and bottom of the sand column? The duration of a constant head permeability test was 30 minutes, during which 1000 ml of water was collected. What is the coefficient of permeability, k (cm/s) for this soil sample? Based on your results for 1b, what type(s) of soils would you expect to the soil sample to be? b. c. 2) A dam has a base of 50 m and length of 100 m (bank-to-bank width). It sits on top of 10 meters of permeable silty sand, underlain by impermeable bedrock. The water level is 15 meters above the datum upstream of the dam, and 3 meters above the datum downstream f the dam. Assume a reasonable value for the coefficient of permeability and estimate the rate of flow through the permeable layer in m'/day

Explanation / Answer

1.a) At the top of the sand column,

Pressure head =0 (no overlying water pressure )

Elevation head = 2.8m

Total head = 2.8+0 = 2.8m

At the bottom of sand column,

Pressure head = 150 cm= 1.5m

Elevation head = 2.3m

Total head = 2.3 + 1.5 = 3.8m

b. Constatnt head permeability is given by

k= V / A * L/ th

= (1000/ 3.14 * 30^2) * ( 150/ 30*60* 50) V= volume of discharged water

= 0.0005 cm/s A= cross-sectional area (cm^2)

L= length of the sample(cm)

t = time (sec)

h= hydraulic head

c. Based on the permeability value, the soil is clean sand and gravel mixture.

2. Given parameters are

length of the dam= 100m

base= 50m

dh= 15-3= 12m

permeability of silty sand k = 10^-7 (assumed)

So,

rate of flow through permeable layer Q = kA* dh/dl

= 10^-7 * (50*100) * (12/100)

= 60* 10-5 m3/day

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