For the soil profile shown in the figure above of Problem 4, when the water table elevation is raised to the top of the ground surface:

(a) What is the change in the effective stress at Point A?

(b) What will be the consequence of the effective stress change?

Assume that the total unit weight of the top soil below the water table will increase 5% from its moist unit weight after raising the water table.

Solutions

Expert Solution

Solution

(a). change in the effective stress at Point A

For initial ground water table:

For lowered ground water table:

(b). Consequence of the effective stress change.

When the water table is upper, the effective stress also changes but it decreases this time because the pore water pressure increase. This increasing of water table level could make the soil swell as its volume increases. This may cause potential problems for underground structures such as buried pipe and other massive underground structures as they may be pushed upward due to the increasing of volume and the buoyancy forces of water.

SUN BUNRA answered 1 year ago

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