FINAL

Question 1

Mohr Circle

Answer 1

Normal Stress on x axis

Shear Stress on y axis

Question 2

Principle Stress

Answer 2

Points at which there is zero shear stress

Question 3

Sign convention for mohrs circle

Answer 3

Compression = Positive 
Counterclockwise = Positive

Question 4

Stresses acting on a vertical plane

Answer 4

Draw a vertical line through the origin of planes

Question 5

Orientation of Principle Planes

Answer 5

Draw line from Op to the major and minor points

Draw element on same line

Question 6

Factors that affect strength of soils

Answer 6

Effective Stress
Density
Rate of Shearing
Nature of Stress Change

Question 7

Mohr-Coulomb Failure Criterion

Answer 7

Failure occurs because of a critical combination of normal stress and shearing stress
On or under the failure envelope
If the circle is tangent to fail envelope then it has reach full strength
Failure does not have to fail at max shear stress (its a combo with normal)
𝜏 = 𝜎’ tan (ɸ) + c

Question 8

Direct Shear Test

Answer 8

Soil in box split across middle
Confining force and constant rate of displacement
Shear force and change in height recorded
Non-uniform failure surface

Question 9

Direct shear on loose sand

Answer 9

Shear increases with shear displacement until a failure shear stress is reached
After fail, shear resistance is constant
Loose sand shows a gradual decrease in volume
Larger confining stress, the larger the max shear stress

Question 10

Direct Shear on dense sand

Answer 10

Shear increases with shear displacement until a failure shear stress is reached and then decreases to the critical state
Volume decreases at first and starts to increase after max shear
Dense soil provides additional resistance to sliding so its “stronger”
Larger confining stress, the larger the max shear stress
Friction angle is larger in dense soils
Very dense tends to act like loose

Question 11

Confining State Friction Angle

Answer 11

tan ɸ’cs = τr / 𝜎 ‘
once the peak strength is hit and the displacement grows
Loose = 28-38
Dense = 35-45

Question 12

Dilation

Answer 12

Change in volume
The lower the normal stress the more dilation
The higher the confining stress, the less diliant

Question 13

Critical State

Answer 13

The same soil and confining stress, the same final residual shear stress no matter if loose or dense

Question 14

Angle of Repose

Answer 14

Friction angle of sand at its loosest state