BASIC TECHNOLOGY LESSON NOTE: Building Construction - Foundation

Building has two parts, namely:

 

1.                   Substructure: the part buried in the ground (foundation);

2.                   Superstructure: the part above the ground (house, workshop, etc)

FOUNDATION is the part of a building which is in direct contact with the ground. Foundation carries the weight (load) of the building.

Foundations are designed to carry three types of load (pressure), namely:

a.            the weight of the building structure;

b.            the weight of goods (e.g. furniture, tv, freezer, water tank) and human beings in the building; and

c.            wind loads – particularly storms.

Functions of foundations

·                A foundation provides the stability against the undermining, souring flood water and the burrowing animals.

·                They transfer the non-uniform load of the superstructure evenly to the sub soil hence it minimize the differential settlement

·                The foundation helps to spread the load of the building evenly over a larger area at a uniform rate so that the load coming over the foundation soil does not exceed the safe bearing capacity.

·                Foundations provide safety against land slide.

·                It provides a level surface for the construction of the superstructure.

Types of foundations

1.        Strip foundation:  this foundation looks like an inverted letter ‘T’. The concrete is spread in the trench at even depth/height. It is the most commonly used type of foundation.

 

Pad Foundation

2.      Pad foundation: this foundation can be either shallow or deep. Shallow pad foundations are used where the loads imposed by a structure are low relative to the bearing capacity of the surface of the floor. But where the bearing capacity of the surface soils is insufficient to support loads imposed, deep pad foundation is used.

 

Raft Foundation

3.      Raft foundation: this foundation is formed by reinforced concrete slabs that cover a wide area, often the entire footprint of a building. It is used in loamy or water logged areas. Some rafts foundations may not require deep trenches like strip and pad foundations.

Most bridges have pile foundations

 

How pile foundation is constructed

4.      Pile foundation: this is a deep foundation. Pile foundations are formed by long, slender, columnar elements often made from steel or reinforced concrete and sometimes timber. The piles are commonly driven into the soil trough weak, compressible strata of water onto stronger, more compact, less compressible and stiffer soil or rock mass. Most bridges are made using pile foundations.

*NOTE: the type of foundation to be used depends on the nature of the soil at the building site and the weight (load) to be carried by the foundation.

SOIL

Soil is the uppermost part of the earth crust in which plants grow.

Soil exists in two layers, namely: top soil or vegetable top soil, and subsoil.

Vegetable top soil may vary in depth down to 300 mm.

Below the vegetable top soil is the subsoil.

The top soil cannot withstand heavy load, hence it is always removed before foundation trenches are made.

In building construction, excavation is the digging and removal of the soil to prepare trenches for constructing foundations. Excavation can be done manually or by the use of machines. 

TYPES OF SOILS FOR BUILDING PURPOSES

1.                   NON-COHESIVE SOIL

2.                   COHESIVE SOIL

3.                   ORGANIC SOIL

4.                   MADE GROUND

MATERIALS FOR MAKING FOUNDATIONS

1.    REINFORCED CONCRETE

2.    CEMENT

3.    AGGREGATE

4.    WATER

5.    MORTAR

EXERCISES:

1.       What are the two parts of a building?

2.       What is foundation?

3.       What are the three main types of load foundations carry?

4.       Sketch and name the four types of foundation.

5.       What is soil?

6.       What are the differences between vegetable top soil and subsoil?

7.       Why is top soil removed before foundation trenches are made?

8.       What is excavation?

9.       What are the characteristics of the four types of building soil?

10.   What are the differences in the load bearing capacity of the four types of building soil?

HOMEWORK

1.             What are four common materials for constructing building walls?

2.             What is the full meaning of DPC?

(Credits: homeimprovementsus.net, www.slideshare.net, www.supercivilcd.com, houseunderconstruction.com, www.skylinesteel.com, http://www.buildinghow.com, http://www.designingbuildings.co.uk )