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Question: question 2 a cylindrical sample of soil is confined in...

Question details

Question 2:

A cylindrical sample of soil is confined in a rigid

-wall permeameter and measures

10 cm in diameter and 20 cm in length. The axis of the cylindrical sample lies in a

horizontal plane. They hydraulic head at the left end of the specimen is controlled

by a reservoir; the water surface in the reservoir i

s exactly 100 cm above the

horizontal axis of the cylindrical soil sample and remains at 100 cm through a

system that automatically adds water to the reservoir if any flows out of the

reservoir. The other (right) end of the soil specimen drains through a t

ube with a

valve. When the valve is closed, there is no flow of water. When the valve is open,

water can flow through the soil. The tube and valve are located along the projection

of the central axis of the sample. When the valve is open, water drips out o

f the

tube such that the water is at atmospheric pressure at the elevation of the central

axis of the sample. When the valve is open, water drips out of the tube such that

the water is at atmospheric pressure at the elevation of the central axis.

a. When the valve is closed, what is (1) the hydraulic gradient across the sample,

(2) the pressure head at the geometric centroid of the soil sample, and (3) the

pore water pressure at the centroid of the sample? Note that the unit weight of

water is 9.81 kN/m

3

.

b. Wh

en the valve is open, what is (1) the hydraulic gradient across the sample,

(2) the pressure head at the geometric centroid of the soil sample, and (3) the

pore water pressure at the centroid of the sample?

c. Open standpipes are attached to the permeameter along the upper boundary.

The standpipes are 1.2 m tall and are installed at the quarter points. Draw a

sketch showing the standpipes and indicate the water levels in the standpipe

when the value on the effluent side of the specimen is open.

d. The soil has a

hydraulic conductivity of 0.001 cm/sec. With the valve open, how

much water (in units of mL) will flow through the soil sample in 5 minutes?

The same permeameter described in problem 2 is packed with 2 different soils,

each having a length of 10 cm. The soil occupying the left side of the permeameter

has a hydraulic conductivity of 0.001 cm/sec while the soil occupying the right side

has a hydraulic conductivity of 0.004 cm/sec. when the valve is open, allowing flow

through the permeameter, what will the pressure head and pore water pressure be

at the geometric centroid of the permeameter (at the interface between the two

soils along the axis of the cylindrical permeameter)? Suppose the soils were

reversed, that is, the soil with the higher hydraulic conductivity is on the left side of

permeameter. Would your answer stay the same or change? If your answer would

change, what would it be?

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