Overview
A foundation is usually the lowest part of a building structure. It is designed to distribute the weight of the structure to the ground below. In this unit you will examine the different types of foundations used in the Caribbean. You will learn factors that dictate the type of foundation that may be used. You will learn the parts and components of a foundation and how to draw sectional details and plans for foundation.
Learning Objectives
After you have completed this unit, you should be able to:
Determine the factors that dictate foundation type selection
List types of foundations
Prepare pictorial and sectional diagrams of various types of foundations
Prepare working foundation plans
Section 1 - Choosing foundation type:
The type of foundation chosen for a building depends on a few key factors. To select an appropriate foundation for a construction every factor must be considered. The major factors to consider for choosing a foundation in the Caribbean include:
The ground: this refers to the type of soil on which the foundation is to be laid. (Stony, clay, sandy etc....)
The nature of the load: this refers to the amount of weight and size of the structure to be placed on the foundation. E.g. (1-storey vs 3-storey, wooden vs concrete, roofing material (galvanize vs concrete))
Water, Water beds and drainage: this refers to the water content of the soil and the proximity of the proposed foundation to the nearby waterbeds. Some foundations may require drainage.
Surface area: this refers to the size of the footprint of the proposed building to be erect. Also, some foundations will not be suitable for small lots.
Accessibility: this refers to how easy it is to get the foundation laid (excavation, concrete pouring etc.)
Section 2 - Types of foundations:
Strip foundations: Strip foundations consist of a continuous concrete footing that distributes the weight to the ground. Footing must be placed under all load bearing walls and more strips are added within the perimeter of the building, with walls that extend up to the floor slab, to provide added structural support. Strip foundations are simple to build and generally require minimal amounts of excavation and labor. Strip foundations are commonly used for firm grounds with good load bearing capacity and can be modified to suit various conditions. Traditional strip foundations are most suitable for soils with good load bearing capacity where settlement or differential settlement is not expected. They are also particularly suitable for light loads. The size of traditional strip foundations is directly related to the walls to be erected on it. The strip should be three times wider than the wall.
Section through a simple strip foundation
Variations of the strip foundation include:
Deep strip foundation: This adaptation of the strip foundation has a much longer and narrower footing. It is more suitable for clayey and marshy soils.
Wide Strip foundation: This adaptation of the strip foundation has wider footing and is suitable for grounds with lower load bearing capacity or underneath walls with bigger loads. Since the footing is wider, it is necessary to reinforce it with steel.
Pad foundations: Pad foundations are the simplest type of foundations. It consists of isolated reinforced concrete slabs that columns or piers sit on. They allow the weight of the structure conveyed by the piers to be distributed over a wider area. These foundations are easy to construct and are also good for slopes where columns are advantageous. Additionally, they can easily be excavated to depths to reach soils with greater load bearing capacity. One cool thing about pad foundations is that it is not limited to the traditional rectangular shape.
Visual Representation of a pad foundation
Section through a pad foundation
Raft Foundation: Raft foundations are usually reinforced concrete slabs that span the entire building area. Since the raft foundation is a slab of equal thickness it also serves as the ground floor slab. Raft foundations contain reinforced beams that improve structural integrity and greatly improve building settlement. These foundations may extend past the perimeter of the building.
Section 3 - Preparing working foundation plans
Checklist:
Obtain a working floor plan
Find out relevant foundation codes and conventions
Select foundation type
Identify load bearing walls that require beams or strips and determine the location of all additional strips or beams necessary
Sketch foundation plan to finalize location of all elements
Complete working drawing of foundation plan to include:
Foundation footing (indicated with hidden detail lines)
Columns, strips or rafts
Dimensions
Labels and title
Appropriate hatching
Example of a Foundation Plan
