Geotechnical Engineering Part 4: Bearing Capacity

Questions and Answers

What is the primary assumption of the upper bound approach in structural analysis?

Exact solution is not achievable

Failure mechanism is assumed (correct)

Failure mechanism is ignored

Ultimate capacity is always lower than the load

What is a characteristic condition for shallow foundations?

D ≤ B (correct)

D = B

D > B

D < 2B

Which type of foundation is categorized under shallow foundations?

Caissons

Strip footing (correct)

Piles with a pile cap

Drilled shafts

What caused the failure of the foundation soil under the Transcona Grain Silos?

Insufficient bearing capacity of the soil Signup and view all the answers

What ratio defines the embedment of shallow foundations?

Df ≤ 2.5B Signup and view all the answers

What remediation methods were applied to the Transcona Grain Silos after the foundation failure?

Building supporting structures and excavating slabs Signup and view all the answers

What must be true about the failure load in the upper bound approach?

It is greater than or equal to the true ultimate capacity Signup and view all the answers

Which criterion states that the applied load must be less than the strength of the soil?

Strength criterion Signup and view all the answers

What year was the Transcona grain elevator built?

1913 Signup and view all the answers

In the context of failure of shallow foundations, what method of analysis assumes the state of stresses at failure?

Lower bound approach Signup and view all the answers

Which company purchased the Transcona grain elevator in 1970?

Parrish & Heimbecker Signup and view all the answers

Which of the following is not a type of shallow foundation?

Drilled pier Signup and view all the answers

What is the allowable bearing capacity equation used for?

To establish the maximum load a foundation can sustain Signup and view all the answers

What type of foundation failure is exemplified in the Transcona Grain Silos case?

Structural Failure Signup and view all the answers

Which of the following statements about structural failure is correct?

It occurs because the structure cannot bear the applied loads Signup and view all the answers

Which condition must be true for a foundation to be considered a shallow foundation?

D ≤ B Signup and view all the answers

Which of the following is an example of a shallow foundation design?

Concrete slab on grade Signup and view all the answers

What does the serviceability criterion involve in foundation design?

Ensuring deformation is within acceptable limits Signup and view all the answers

What does the term Nc represent in the bearing capacity equation?

Cohesion bearing capacity factor Signup and view all the answers

In Terzaghi’s Bearing Capacity Equation, what does the term $q_0$ represent?

Existing stress at the level of the footing Signup and view all the answers

How is the bearing capacity factor Ng calculated in relation to the friction angle?

It is directly proportional to the square of the friction angle. Signup and view all the answers

What is the purpose of the bearing capacity factors Nc, Nq, and Ng in the equation proposed by Terzaghi?

To adjust bearing capacity calculations based on soil parameters Signup and view all the answers

Which of the following describes Terzaghi's Bearing Capacity Equation?

It is meant for shallow strip footings. Signup and view all the answers

What is one of the significant aspects of the equation $q_u = cN_c + q_0 N_q + 0.5 gBN_g$?

It takes into account the effective stress within the soil. Signup and view all the answers

How can the empirical equation for Kpg be summarized?

It is a quadratic function of the friction angle. Signup and view all the answers

What is the significance of the bearing capacity equation first proposed by Terzaghi in 1943?

It introduced empirical relationships for bearing capacities. Signup and view all the answers

What is the bearing capacity equation for circular footings?

qu = 1.3cNc + qoNq + 0.3gBNg Signup and view all the answers

Which type of soil is associated with punching shear failure?

Loose or soft soils Signup and view all the answers

What characterizes general shear failure?

Sudden failure with dense or stiff soils Signup and view all the answers

What adjustment is required for local shear failure in bearing capacity equations?

Apply corrections to the equations Signup and view all the answers

In which type of failure is there typically no heave observed?

Punching shear failure Signup and view all the answers

What does the factor 0.5 represent in the bearing capacity equation for rectangular footings?

Contribution of soil weight Signup and view all the answers

What does the term 'qo' represent in bearing capacity equations?

Additional surcharge load Signup and view all the answers

What is the formula used for calculating the design cohesion in local or punching shear failure?

f design = tan(-1)(tan(f)) Signup and view all the answers

What type of strength parameters should be used for effective stress analysis in drained conditions?

Effective cohesion, c' Signup and view all the answers

Which of the following statements is true regarding undrained analysis?

It is applicable immediately after loading in clays. Signup and view all the answers

What happens to pore pressure in undrained conditions during loading?

It increases and may take time to dissipate. Signup and view all the answers

In a drained analysis, how should the water table be considered?

It has no effect in total stress analysis. Signup and view all the answers

Which parameter should be used to determine unit weight of soil when the water table is at or above the foundation base?

Submerged unit weight, g' Signup and view all the answers

What is the effective friction angle in undrained conditions for saturated normally consolidated clay?

Zero Signup and view all the answers

In a total stress analysis, how does the water table affect the analysis?

It can be ignored in drained analysis. Signup and view all the answers

Which of the following parameters is not used in undrained strength analysis?

Effective cohesion, c' Signup and view all the answers

Study Notes

Types of Foundations

Foundations are categorized into shallow and deep foundations.
Shallow foundations include mat or raft and pad footings.
Deep foundations typically consist of piles with a pile cap.

Shallow Foundations

Shallow foundations are defined by the relationship where the depth of embedment (D) is less than or equal to the breadth (B).
Types include strip footings, circular, square, and rectangular footings.

Definition of Shallow Foundations

The ratio of embedment depth (Df) to minimum dimension (B) should not exceed 2.5.

Geotechnical Design Criteria

Strength criterion necessitates that applied loads must be less than soil strength.
Serviceability criterion requires that deformation remains within acceptable limits.

Failure of Shallow Foundations

Two analysis methods:
- Lower bound assumes stress states at failure; yields a failure load less than or equal to true ultimate capacity.
- Upper bound assumes failure mechanisms; provides a failure load greater than or equal to true ultimate capacity.
An exact solution is identified when both methods yield the same result.

Case Study: Transcona Grain Silos

Built by Canadian Pacific Railway in 1913, the foundation failed due to inadequate soil bearing capacity.
Remediation included supporting structures and excavation to restore the foundation.

Types of Failure

General shear failure: characterized by sudden failure and surface heave, typical in dense or stiff soils.
Local shear failure: occurs in medium-compacted soils, leading to minor heave and settlement.
Punching shear failure: results from foundation compaction under loose or soft soils, causing settlement without heave.

Bearing Capacity Equation

Terzaghi's equation for shallow strip footings:
- ( q_u = cN_c + q_o N_q + 0.5 \gamma BN_g )
Variations for square and circular footings adjust the bearing capacity factors (Nc, Nq, Ng).

Selection of Parameters

Drained conditions apply for clays after long periods and always for sands, using effective strength parameters.
Undrained conditions apply to clays immediately post-loading, requiring undrained strength parameters.

Unit Weight of Soil

When analyzing bearing capacity, identify the unit weight of soil (γ) and consider the water table's position.
In undrained analysis, the water table has minimal effect; however, in drained analysis, utilize effective overburden pressure.

Practical Considerations

If the water table is at or above the foundation base, use submerged unit weight.
Water table effects can vary depending on its location relative to the foundation dimensions, influencing effective stress.

This summary encapsulates key concepts and findings in geotechnical engineering as they relate to shallow foundations and their bearing capacities.

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Description

This quiz covers the essential concepts of bearing capacity related to shallow foundations in Geotechnical Engineering. It examines various types of foundations, design criteria, allowable bearing capacity, and potential failure modes. Ideal for students looking to deepen their understanding of foundation engineering.

Geotechnical Engineering Part 4: Bearing Capacity

Questions and Answers

What is the primary assumption of the upper bound approach in structural analysis?

What is a characteristic condition for shallow foundations?

Which type of foundation is categorized under shallow foundations?

What caused the failure of the foundation soil under the Transcona Grain Silos?

What ratio defines the embedment of shallow foundations?

What remediation methods were applied to the Transcona Grain Silos after the foundation failure?

What must be true about the failure load in the upper bound approach?

Which criterion states that the applied load must be less than the strength of the soil?

What year was the Transcona grain elevator built?

In the context of failure of shallow foundations, what method of analysis assumes the state of stresses at failure?

Which company purchased the Transcona grain elevator in 1970?

Which of the following is not a type of shallow foundation?

What is the allowable bearing capacity equation used for?

What type of foundation failure is exemplified in the Transcona Grain Silos case?

Which of the following statements about structural failure is correct?

Which condition must be true for a foundation to be considered a shallow foundation?

Which of the following is an example of a shallow foundation design?

What does the serviceability criterion involve in foundation design?

What does the term Nc represent in the bearing capacity equation?

In Terzaghi’s Bearing Capacity Equation, what does the term $q_0$ represent?

How is the bearing capacity factor Ng calculated in relation to the friction angle?

What is the purpose of the bearing capacity factors Nc, Nq, and Ng in the equation proposed by Terzaghi?

Which of the following describes Terzaghi's Bearing Capacity Equation?

What is one of the significant aspects of the equation $q_u = cN_c + q_0 N_q + 0.5 gBN_g$?

How can the empirical equation for Kpg be summarized?

What is the significance of the bearing capacity equation first proposed by Terzaghi in 1943?

What is the bearing capacity equation for circular footings?

Which type of soil is associated with punching shear failure?

What characterizes general shear failure?

What adjustment is required for local shear failure in bearing capacity equations?

In which type of failure is there typically no heave observed?

What does the factor 0.5 represent in the bearing capacity equation for rectangular footings?

What does the term 'qo' represent in bearing capacity equations?

What is the formula used for calculating the design cohesion in local or punching shear failure?

What type of strength parameters should be used for effective stress analysis in drained conditions?

Which of the following statements is true regarding undrained analysis?

What happens to pore pressure in undrained conditions during loading?

In a drained analysis, how should the water table be considered?

Which parameter should be used to determine unit weight of soil when the water table is at or above the foundation base?

What is the effective friction angle in undrained conditions for saturated normally consolidated clay?

In a total stress analysis, how does the water table affect the analysis?

Which of the following parameters is not used in undrained strength analysis?

Study Notes

Types of Foundations

Shallow Foundations

Definition of Shallow Foundations

Geotechnical Design Criteria

Failure of Shallow Foundations

Case Study: Transcona Grain Silos

Types of Failure

Bearing Capacity Equation

Selection of Parameters

Unit Weight of Soil

Practical Considerations

Studying That Suits You

Description

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