Types of Shallow Foundation

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Questions and Answers

What is the maximum depth for constructing a spread footing economically?

1 m

10 m

3 m (correct)

5 m

Which type of footing is suitable for walls and masonry columns?

Strip footing

Spread footing (correct)

Grillage footing

Mat foundation

What feature distinguishes shallow foundations from other types?

They are always made of concrete

They transfer loads at deep levels

The depth is less or equal to the width (correct)

The depth is greater than the width

Which of the following types of shallow foundation is not correct?

Deep footing Signup and view all the answers

What mixture is typically used in constructing a spread footing?

1:4:8 Signup and view all the answers

What term is used to refer to shallow foundations, emphasizing their construction near the ground surface?

Open foundations Signup and view all the answers

In which type of shallow foundation is the base wider than the top?

Spread footing Signup and view all the answers

Which characteristic of a shallow foundation relates to its load transfer mechanism?

Transfers loads at a shallow depth Signup and view all the answers

What is the usual projection of bed concrete from the lowest course of foundation masonry?

150 mm Signup and view all the answers

Which type of footing supports only one column?

Isolated Footing Signup and view all the answers

In which scenario is a combined footing most likely used?

Column close to property boundary Signup and view all the answers

What type of footing is common to more than two columns in a row?

Continuous Footing Signup and view all the answers

What is the primary design concern for an inverted arch footing?

Resistance to horizontal thrust Signup and view all the answers

How would you categorize a footing that is a beam connecting two columns?

Strip Footing Signup and view all the answers

What characteristic defines a continuous footing?

Common to multiple columns in a row Signup and view all the answers

Why might a continuous footing be preferred when soil bearing capacity is low?

Distributes loads evenly Signup and view all the answers

What is an eccentrically loaded footing?

A footing where the center of gravity does not coincide with the supporting area Signup and view all the answers

Which type of footing is beneficial when multiple columns have extensive loads or the soil's SBC is low?

Mat footing Signup and view all the answers

What type of mat footing is described as having a slab thickness exceeding 90 cm?

Cellular footing Signup and view all the answers

What is the primary purpose of a grillage footing?

To spread heavy loads over a larger area of poor soil Signup and view all the answers

What describes the structure of grillage foundations?

Utilizes multiple tiers of I-section steel beams Signup and view all the answers

In a grillage foundation, what is the minimum required clear space between the flanges of adjacent grillage beams?

75 mm Signup and view all the answers

Which of the following is a type of grillage foundation that avoids differential settlement?

Timber grillage Signup and view all the answers

What is the function of pipe separators in a grillage foundation?

To maintain spacing between grillage beams Signup and view all the answers

Which type of shallow foundation is specifically designed for a single column?

Individual Footing Signup and view all the answers

What is the main purpose of a combined footing?

To accommodate several overlapping footings Signup and view all the answers

Which of these footings is used for walls and wider load-bearing applications?

Spread Footings Signup and view all the answers

For a square footing with a vertical load of 200 kN and a safe bearing capacity of 100 kN/m2, what is the length of each side?

1.414 m Signup and view all the answers

What is the primary method used for constructing drilled shafts?

Auger drilling Signup and view all the answers

Which type of footing would be most appropriate for a situation where eccentric loads are encountered?

Isolated Footing Signup and view all the answers

In what soil conditions are drilled shafts or caissons generally unsuitable?

Deep deposits of soft clays Signup and view all the answers

What is a key characteristic of mat or raft foundations?

They spread load over a large area. Signup and view all the answers

Which type of foundation is more capable of transferring larger column loads?

Drilled shafts Signup and view all the answers

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

Piled Foundation Signup and view all the answers

What is a distinguishing feature of drilled shafts compared to pile foundations?

They provide higher load capacities. Signup and view all the answers

What shape is a typical combined footing?

Rectangle Signup and view all the answers

What depth range is suitable for the use of drilled shafts or caissons?

From 10m to 100m Signup and view all the answers

Which type of footing is used for preventing differential settlement of individual footings?

Raft or mat foundation Signup and view all the answers

What term is used to describe the combination of shaft resistance and toe resistance in drilled shafts?

Total bearing capacity Signup and view all the answers

What defines a combined footing?

When two or more columns share a footing. Signup and view all the answers

Study Notes

Shallow Foundation

Types of Shallow Foundation
- Spread Footing
  - A widened base distributes load over a larger area
  - Suitable for walls & masonry columns
  - Three types:
    - Isolated Column Footing/Isolated Footing
      - A separate footing for each column
      - Designed to distribute loads evenly
      - Constructed on a concrete bed
    - Combined Footing
      - Supports two or more columns with a single base
      - Used when columns are close to property boundaries
      - Can be rectangular or trapezoidal
      - A strap beam connects the columns
    - Continuous Footing
      - A footing shared by multiple columns in a row
      - More suitable for closely spaced columns or low soil bearing capacity
- Strip Footing
  - An independent footing connecting two columns with a beam
  - Types include:
    - Inverted Arch Footing
      - Used for poor soil bearing capacity where load is transferred through walls
      - Inverted arches distribute weight between walls
      - End walls need to withstand outward horizontal thrust
    - Eccentrically Loaded Footing
      - The center of gravity doesn’t align with the footing’s supporting area
      - Designed to account for uneven load distribution
- Mat Footing/Raft Footing
  - Used for extensive loads, particularly with multistory buildings
  - Overlapping footings create a continuous base for multiple columns
  - Helps ensure uniform settlement of the structure to prevent uneven stress
  - Three types based on slab thickness:
    - Slab (Solid) - up to 30 cm
    - Slab and Beam - over 30 cm
    - Cellular - over 90 cm
- Grillage Footing
  - Used for heavy loads from steel columns when soil bearing capacity is low
  - Consists of multiple tiers of I-section steel beams
  - Top tier has fewer but larger steel sections
  - Bottom tier has more numerous but smaller steel sections
  - Beams are encased in concrete and spaced apart to allow proper concreting

Deep Foundation

Pile Foundation
- Used when soil bearing capacity is weak at shallow depths
- Piles extend into deeper, stronger soil strata
- Transferred loads through friction resistance or end-bearing capacity
- Suitable for structures subjected to high lateral and uplift forces
Drilled Shafts or Caissons
- High capacity cast-in-place foundations similar to pile foundations
- Resist loads through shaft resistance, toe resistance, or a combination of both
- Constructed using an auger for deeper installation
- Can transfer greater loads than pile foundations
- Suitable for depths between 10 to 100 metres
- Not suitable for soft clays, loose water-bearing soils, caving formations, soils with boulders, or artesian aquifers

Comparison

Isolated vs. Combined Footing: Combined footings are used when multiple columns are close together and their individual footings overlap. They are essentially a combination of isolated footings.
Pile Foundation vs. Drilled Shafts: Drilled shafts are similar to pile foundations but offer higher capacity and are used for greater depths.
Raft Foundations: Used to distribute loads from walls and columns when soil bearing capacity is low. They act as a single combined footing for the entire structure.

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Description

Explore the various types of shallow foundations, including spread footings such as isolated, combined, and continuous footings. Understand how these foundations distribute loads and their suitability for different construction needs. Test your knowledge on the essential concepts and applications.