Podcast
Questions and Answers
What is the primary difference between gross pressure (qg) and net pressure (qn)?
What is the primary difference between gross pressure (qg) and net pressure (qn)?
- Gross pressure is the pressure exerted by the foundation, while net pressure is the pressure exerted by the soil
- Gross pressure is the total pressure at the base of the foundation, while net pressure is the pressure in excess of the pressure due to the soil (correct)
- Gross pressure is the pressure exerted by the building, while net pressure is the pressure exerted by the foundation
- Gross pressure includes the weight of the soil, while net pressure does not
What is the relationship between net ultimate bearing capacity (qnu) and ultimate bearing capacity (qu)?
What is the relationship between net ultimate bearing capacity (qnu) and ultimate bearing capacity (qu)?
- qnu = qu / Df
- qnu = qu * Df
- qnu = qu - Df (correct)
- qnu = qu + Df
Which type of soil failure is associated with a well-defined wedge pattern?
Which type of soil failure is associated with a well-defined wedge pattern?
- General shear failure
- Punching shear failure
- Local shear failure (correct)
- All of the above
What is the relationship between safe bearing capacity (qs) and net safe bearing capacity (qns)?
What is the relationship between safe bearing capacity (qs) and net safe bearing capacity (qns)?
Which of the following is NOT a factor in determining the net safe bearing capacity (qns)?
Which of the following is NOT a factor in determining the net safe bearing capacity (qns)?
Which type of soil failure is associated with a well-defined failure pattern and is characteristic of dense sand?
Which type of soil failure is associated with a well-defined failure pattern and is characteristic of dense sand?
What is the primary difference between general shear failure and punching shear failure?
What is the primary difference between general shear failure and punching shear failure?
Which of the following is NOT a type of shallow foundation?
Which of the following is NOT a type of shallow foundation?
Which foundation type is typically used for structures with heavy and concentrated loads?
Which foundation type is typically used for structures with heavy and concentrated loads?
Which code or standard is typically used to design shallow foundations in the United States?
Which code or standard is typically used to design shallow foundations in the United States?
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Study Notes
Foundation Types
- Shallow Foundations: Suitable for conditions where B > Df (width > depth) and offer cost-effective solutions.
- Deep Foundations: Required when Df > B (depth > width) demonstrating increased support for structures in unfavorable soil conditions.
Soil Conditions and Recommendations
- Dense and compact sands provide strong support, suitable for shallow and deep foundations.
- Loose sand may necessitate deep foundations due to its compressible nature.
- Soft clay: characterized by low bearing capacity, can extend up to significant depths; may require special foundation types like piles.
- Medium to stiff clay: generally provides better support with increased stiffness slightly alleviating the need for deeper foundations.
Foundation Options Based on Soil Type
- Raft foundations may be necessary in areas with soft soil.
- Pile foundations can be adapted for various soil conditions, including drilled piers and driven piles for greater stability in soft or loose soils.
- Use of friction piles and end-bearing piles depending on the soil stratification and load requirements.
Codes and Standards
- IS: 1904 outlines design and construction practices for foundations in soil; reaffirmed multiple times.
- IS: 6403 focuses on the bearing capacity determination for shallow foundations.
- Eurocode 7 provides guidelines for geotechnical design and works examples.
Earthquake Resistant Design
- Foundations must be designed to withstand seismic forces as part of earthquake-resistant design principles.
- Topics include bearing capacity, combined footings, raft foundations, and dynamic loading considerations.
General Design Requirements
- The selection of foundation types must consider the mechanical properties of soil and structural load demands.
- Understanding modes of soil failure is crucial in foundation design to prevent structural issues and ensure longevity.
Recommended Practices
- Engineers typically favor shallow foundations for economic reasons, unless soil inadequacies dictate otherwise.
- Ensure thorough geological assessment to identify the best foundation choice and avoid settlement issues detrimental to structural integrity.
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