Soil Mechanics Midterm Exam Time: 2 hours

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1. The wet densities (ρ) and degrees of saturation (S) of a soil are given in the following table:

ρ(kg/m3) S (%) 1694 50 1806 75

a. Determine void ratio (e). b. Determine specific gravity (Gs).

(15 points)

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2. Describe the atomic structure and engineering properties of Smectit, briefly. (15 points).

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3. The laboratory test data for a standard Proctor test are given in the table below:

Volume of Proctor Mold (cm3) Mass of Wet Soil in the Mold (kg) Water Content (%) 943.3 1.76 12 943.3 1.86 14 943.3 1.92 16 943.3 1.95 18 943.3 1.93 20 943.3 1.90 22

a. Find the maximum dry unit weight. b. Find the optimum moisture content.

(15 points)

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4. The section through a dam is shown in the following figure. The coefficient of permeability of the foundation soil is 2.5×10-5 m/s. Find the total uplift force (25 points).

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5. A specimen of sand is tested in direct simple shear. The stress conditions in the test are as shown in the following figures.

Initial conditions:

σv = 4.00 kg/cm2 σh = 2.00 kg/cm2

At failure:

σv = 4.00 kg/cm2 σh = 2.00 kg/cm2 τhv = 2.00 kg/cm2

a. Determine the magnitude and orientation of the principal stresses at failure. b. What is the orientation of the failure plane?

(30 points)