Geotechnical Analysis, Lecture 1 and 2

Question 1

What is the role of foundations in a structure?

Answer 1

To transfer the load from the structure to the soil.

Question 2

What two main factors are calculated in foundation design?

Answer 2

Soil capacity and resistance.

Question 3

How does the stress-strain curve behave for soils?

Answer 3

It is non-linear and plateaus.

Question 4

What is a monopile and where is it used?

Answer 4

A steel foundation used in offshore constructions, cost-effective for shallow waters.

Question 5

How does geothermal energy provide heating and cooling?

Answer 5

By utilising natural temperature differences in the air and ground.

Question 6

What is liquefaction in geotechnics?

Answer 6

Soil acts like a liquid during vibrations, as water trapped in it reduces strength

Question 7

What is scour and why is it problematic?

Answer 7

Erosion of soil by water around foundations, leading to loss of support.

Question 8

What is punch-through in geotechnics?

Answer 8

Uneven soil failure under a load, causing deflection or rapid settlement.

Question 9

What geometry and loading conditions are required in design?

Answer 9

Basic structure geometry and the loading conditions it will experience.

Question 10

What factors are considered in geotechnical site investigations?

Answer 10

Soil stratigraphy, soil strength, soil stiffness, and groundwater conditions.

Question 11

Why must the location of services be identified?

Answer 11

To avoid conflicts with gas, water, electricity, sewers, or tunnels.

Question 12

What information is needed about nearby buildings?

Answer 12

The type and depth of their foundations.

Question 13

What must be considered about a structure’s performance?

Answer 13

Any restrictions or limitations on its behavior.

Question 14

What is the primary design objective for geotechnical structures?

Answer 14

To create a safe and stable structure.

Question 15

What does local stability address in geotechnical design?

Answer 15

Instability of the structure itself, not the soil.

Question 16

What is overall stability in geotechnical design?

Answer 16

Stability involving large-scale soil failure, such as slope instability or excavation slip surfaces.

Question 17

What must be demonstrated when analyzing structural forces?

Answer 17

A sufficient factor of safety

Question 18

What is the equation for FoS?

Answer 18

Q_ult/Q_wrk > 1.0

Question 19

Why are movements analysed in geotechnical structures?

Answer 19

To ensure serviceability of the structure and account for effects like excavation.

Question 20

What are the theoretical requirements?

Answer 20

• Equilibrium
• Compatibility
• Constitutive behaviour
• Boundary conditions”

Question 21

What is the equilibrium condition in geotechnical analysis?

Answer 21

The sum of external forces equals the sum of internal forces.

Question 22

What are the internal forces?

Answer 22

Direct and shear stresses

Question 23

What is compatibility in deformation?

Answer 23

Deformations must remain continuous across materials or joints.

Question 24

How do compatible deformations differ from non-compatible?

Answer 24

• Compatible: Continuous deformation (e.g., stretched plate).
• Non-Compatible: Disjointed deformation (e.g., ruptured plate).

Question 25

What does constitutive behavior describe?

Answer 25

Describes how a material responds to stress, defining the relationship between stress and strain. It explains the material’s mechanical behavior under different loading conditions, such as elastic, plastic, or strain-hardening responses.

Question 26

What is strain hardening in soils?

Answer 26

A process that strengthens and hardens a material by deforming it plastically.

Question 27

What is the constitutive matrix equation?

Answer 27

{Δσ} = [D]{Δε}

Question 28

What does a constitutive equation describe?

Answer 28

Constitutive equations tell us how a solid deforms (in time) as a response to stresses, to changes of temperature and to changes of pore pressure among others.