
(a)
Find the change in effective stress
(a)

Answer to Problem 9.4P
The change in effective stress at point C when the water table drops by 2 m is
Explanation of Solution
Given information:
The thickness
The thickness
The thickness
The void ratio (e) of soil in the first layer is 0.7.
The specific gravity
The void ratio (e) of soil in the second layer is 0.55.
The depth (h) of water table drop is 2 m.
Calculation:
Determine the dry unit weight
Here,
Take the unit weight of the water as
Substitute 2.69 for
Determine the dry unit weight
Substitute 2.7 for
Determine the saturated unit weight
Substitute
Calculate the total stress at point C (13 m) using the relation.
Substitute
Calculate the pore water pressure at point C (13 m) using the relation.
Substitute
Calculate the effective stress at point C (13 m) using the relation.
Substitute
Water table drops by 2 m:
Calculate the total stress at point C when the water level drops by 2 m using the relation.
Substitute
Calculate the pore water pressure at point C when the water table drops by 2 m using the relation.
Substitute
Calculate the effective stress at point C when the water table drops by 2 m using the relation.
Substitute
Determine the change in effective stress when the water level drops by 2 m from the original position using the relation;
Substitute
Thus, the change in effective stress at point C when the water table drops by 2 m is
(b)
The change in effective stress
(b)

Answer to Problem 9.4P
The change in effective stress at point C rises to the surface up to point A is
Explanation of Solution
Given information:
The thickness
The thickness
The thickness
The void ratio (e) of soil in the first layer is 0.7.
The specific gravity
The void ratio (e) of soil in the second layer is 0.55.
Calculation:
Determine the saturated unit weight
Substitute
Calculate the total stress at point C (13 m) using the relation.
Substitute
Calculate the pore water pressure at point C (13 m) using the relation.
Substitute
Calculate the effective stress at point C (13 m) using the relation.
Substitute
Water table rises to the surface up to point A:
Determine the change in effective stress when the water table rises to the surface up to point A using the relation;
Substitute
Thus, the change in effective stress at point C rises to the surface up to point A is
(c)
Find the change in effective stress
(c)

Answer to Problem 9.4P
The change in effective stress at point C when the water level rises 3 m above point A due to flooding is
Explanation of Solution
Given information:
The thickness
The thickness
The thickness
The void ratio (e) of soil in the first layer is 0.7.
The specific gravity
The depth (h) of water rises above point A is 3.0 m.
Calculation:
Calculate the total stress at point C (16 m) using the relation.
Substitute
Calculate the pore water pressure at point C (16 m) using the relation.
Substitute
Calculate the effective stress at point C (16 m) using the relation.
Substitute
Water level rises 3 m above point A due to flooding:
Determine the change in effective stress when the water level rises 3 m above point A due to flooding using the relation;
Substitute
Thus, the change in effective stress at point C when the water level rises 3 m above point A due to flooding is
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Chapter 9 Solutions
Principles of Geotechnical Engineering (MindTap Course List)
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