Lecture 12

Question 1

How does the development and construction of civil engineering infrastructure play a role in the interaction with soil?

Answer 1

Alters the state of the soil(s)

Question 2

What must be accounted for in geotechnical analysis?

Answer 2

Changes in the soil state, e.g., density, stress, fabric

Question 3

What increases as you go deeper into the soil?

Answer 3

Gravity and stress state

Question 4

When is there an isotropic stress condition?

Answer 4

If 3 arrows have the same magnitude

Question 5

When is there a bi-axial stress condition and an axes symmetric stress condition?

Answer 5

If only 2 arrows same magnitude

Question 6

What are the characteristics of stress?

Answer 6

• Non scalar quantity
• Direction-dependent
• Uses a matrix

Question 7

What are characteristics of pressure?

Answer 7

• Scalar quantity → single parameter
• Same in all directions

Question 8

What does hydrostatic mean?

Answer 8

• Complete saturated conditions, no flow
• That value of pressure will increase from zero at the top and the increase will be linear

Question 9

How can pore water pressure be calculated?

Answer 9

u = 𝛾_wz = ρ_wgz

Question 10

What is the pressure head?

Answer 10

Pressure head = energy in a material divided by height in the water

Question 11

What stresses increase the most in soil?

Answer 11

Vertical

Question 12

How are vertical stresses defined?

Answer 12

Typically defined in terms of total and effective stress components

Question 13

Why do vertical stresses exist?

Answer 13

This may be due to the self-weight of soil and/or external loads

Question 14

How does total vertical stress change with depth?

Answer 14

Increases linearly

Question 15

What is the total vertical stress in dry homogeneous soil?

Answer 15

σ_z=𝛾_dz

Question 16

What is the total vertical stress in water or saturated soil?

Answer 16

σ_z=𝛾_sz

Question 17

What is pore pressure?

Answer 17

This is the pressure in the water filling the voids of saturated soil

Question 18

How does pore pressure change with depth?

Answer 18

Increases linearly

Question 19

What is the effective stress?

Answer 19

• Net stress supported by the soil skeleton
• Upwards direction
• Controlled by soils fabric

Question 20

How can effective stress be calculated?

Answer 20

σ’_z=σ_z-u

Question 21

What do changes in effective stress affect?

Answer 21

Compression, distortion, and shearing resistance

Question 22

How do effective vertical stresses change with depth in a homogeneous soil?

Answer 22

Increase linearly

Question 23

How does water rise in capillary tubes?

Answer 23

Due to surface tension effect
- Surface tension forces pull water inside the tube until their vertical components are in equilibrium with the weight of water inside the tube

Question 24

How does capillary rise work?

Answer 24

Like a suction

Question 25

What will the pore pressure be at the height of the water in capillary tube?

Answer 25

Negative

Question 26

What does a smaller pore space mean?

Answer 26

More suction of water

Question 27

What is capillary rise height directly proportional to?

Answer 27

1/d

Question 28

How can pore water pressure in the capillary zone in sands be estimated?

Answer 28

u = -(h_c𝛾_wS_r)

Question 29

When does the equation for pore water pressure in sand not apply?

Answer 29

Doesn’t apply when underwater and in completely dry conditions

Question 30

How can the height of the sand column in contact with water be calculated?

Answer 30

h = C/e*D_10
- e void ratio
- C - constant
- D_10 effective size