Mohrs Circle and NC or OC

Question 1

True or False: The triaxial test is only applicable to clays.

Answer 1

False. It is suitable for all soil types.

Question 2

What type of stress condition is applied in a triaxial test?

Answer 2

Axi-symmetric condition.

Question 3

Fill in the blank: The all-round pressure applied is called the ___ pressure.

Answer 3

Cell pressure (CP)

Question 4

What does CP represent in a triaxial test?

Answer 4

CP = Cell Pressure = σ_r = σ_c

Question 5

What are the two main stages of a triaxial test?

Answer 5

(1) Consolidation stage, (2) Shearing stage.

Question 6

What device measures volume change in the apparatus?

Answer 6

Drainage valve and volume measurement system (e.g., burette or gauge).

Question 7

True or False: The latex membrane used in a triaxial test is permeable to water.

Answer 7

False. It is impermeable.

Question 8

What does “isotropic loading” mean in the context of the triaxial test?

Answer 8

Equal stress applied in all directions with no drainage.

Question 9

What does U-U stand for?

Answer 9

Unconsolidated-Undrained

Question 10

Formula: What is deviator stress in a U-U test?

Answer 10

σ_a - σ_r

Question 11

What is the corrected area formula for undrained conditions?

Answer 11

A = A_0 / (1 - ε_a)

Question 12

Match: < 20 kPa → __; 20–40 kPa → __; 40–75 kPa → __; 75–150 kPa → __; > 150 kPa → __

Answer 12

very soft; soft; firm; stiff; very stiff

Question 13

In U-U test Mohr’s circle, what are σ_a and σ_r?

Answer 13

Major and minor principal stresses respectively.

Question 14

What does C-U stand for?

Answer 14

Consolidated-Undrained

Question 15

Fill in the blank: In a C-U test, drainage is allowed during ___ but closed during ___.

Answer 15

Consolidation; shearing

Question 16

What is the effect of using back pressure in a C-U test?

Answer 16

Helps maintain full saturation.

Question 17

In a C-U test, effective stress parameters obtained are:

Answer 17

c’ and φ’

Question 18

What stress components define Mohr’s circle in 2D?

Answer 18

σ_x, σ_z, τ_xz

Question 19

Fill in the blank: By moment equilibrium, τ_zx = τ_xz.

Answer 19

True

Question 20

What is the sign convention for shear stresses in Mohr’s circle?

Answer 20

Clockwise shear stresses are negative.

Question 21

What is the pole in Mohr’s circle?

Answer 21

A point from which a line to any point on the circle is parallel to the plane on which the stresses act.

Question 22

True or False: The pole method helps determine stress on arbitrary planes.

Answer 22

True

Question 23

How do you find the pole if the stress and plane are known?

Answer 23

Project lines from known stress points Q and R.

Question 24

What are principal planes?

Answer 24

Planes where shear stress is zero and normal stress is either max or min.

Question 25

Fill in the blank: The directions of principal stresses are ___.

Answer 25

Orthogonal

Question 26

In triaxial tests, what are typically the principal stresses?

Answer 26

σ_1 and σ_3

Question 27

What angle does the failure plane make with the horizontal in triaxial tests?

Answer 27

θ = 45° + φ'/2

Question 28

What is the formula for normal and shear stress on plane AB?

Answer 28

σ_n' = ½(σ_1' + σ_3') + ½(σ_1' - σ_3')cos(2θ); τ = ½(σ_1' - σ_3')sin(2θ)

Question 29

What dictates the orientation of the failure plane in the shear box test?

Answer 29

Boundary conditions of the apparatus

Question 30

True or False: In the shear box, the failure plane is imposed, not freely developed.

Answer 30

True

Question 31

What is a stress path?

Answer 31

A sequence of stress states during loading, shown as Mohr’s circles or stress points.

Question 32

What does the horizontal distance between TSP and ESP represent?

Answer 32

Pore water pressure

Question 33

Fill in the blank: s' = ½(σ_1' + σ_3'), t' = ½(σ_1' - σ_3')

Answer 33

True

Question 34

True or False: t = t′ for undrained conditions.

Answer 34

True

Question 35

During undrained shearing of NC clays, what happens to effective stress?

Answer 35

It decreases as pore pressure increases.

Question 36

What is the slope of the ESP for NC clay in CU test?

Answer 36

Slope = 1

Question 37

What happens to pore water pressure during shearing of OC clay?

Answer 37

It decreases (soil dilates)

Question 38

True or False: The stress path for OC clay in CU test diverges from NC clay.

Answer 38

True