There are different types of foundation available and each is unique to the soil that it would be constructed on. Let’s take at a look at some foundations and how they are constructed.
Traditional strip or Orthodox
This is the oldest and most common form of foundation. Method of construction is, the trench is excavated, concrete is placed in the bottom and the wall is built on it. The width is governed by the relationship between the imposed loads and the bearing capacity of the soil; and by the practical necessity for operative to work in the trench.
Wide Strip Foundations
This foundation is used where the load bearing capacity of the ground is low. For example in: marshy ground, soft clay silt and made-up ground.
Weft strip foundations are:
o A variation of the traditional strip
o It spreads the load over a larger area of soil
o It is usual to provide transverse and longitudinal reinforcement to the withstand the tension that will arise from the building load
o The depth below the ground can be the same as for traditional or orthodox strip foundation
Inverted ‘T’ Beam
This is one of the best; you don’t have to worry about the soil.
o It is an alternative to the wide strip foundation
o It is a form of wide strip foundation with an up stand beam
o It carries both transverse and longitudinal reinforcement
o This Type of foundation s used in expansive clay soils
Deep Strip or Trench Fill Foundation
o A variation to the traditional strip
o It was first introduced to reduce the expense entailed in constructing the traditional strip foundation to depths of nine hundred millimeters or more in shrinkable soils and to counteract the variable soil conditions.
This type a foundation can prove economic. Why?
o When excavated by machine the volume of excavated earth is reduced
o Trench is reduced
o Back fill and surplus soil are also reduced
o There is also time saving due to quicker completion
o Reinforcement if necessary
Stepped Foundations
Foundation must be horizontal unless of course they are required to resist inclined thrust from walls or some arched forms. To put strip foundations on a sloping site at the same level will mean deep trenches for those on higher since they will be at a good depth below ground level, necessitating excessive walling in the soil.
The excessive building into the soil may be reduced by:
i. Cut only
ii. Fill only
iii. Cut and fill, so as to provide a horizontal plane to build on or stepping the foundations of the wall down the slope, parallel to the slope. These are called step foundations.
Isolated Column Foundations (also called pad foundations)
Isolated column foundations is an independent square or rectangular concrete slab with a pier or column bearing in the centre of it. Usually this is used to support framed structures on uniform, firm and stable soils.
Continuous Column Foundation
Continuous column foundation is a concrete strip carrying a line of columns. Such a foundation may be used because where:
1. Spacing in one direction and loading of columns are such that the edges of adjacent individual pads touch or overlap.
2. The spread of foundation at right angles to the line of columns is restricted, say by site boundary building and so prevents the independent pads of adequate size.
Combined Column Foundations
The foundations of adjacent columns are combined when:
1. A column is close to the boundary of the site that a separate foundation would be eccentrically loaded and
2. Where foundations of adjacent columns are linked to resist uplift, overturning or opposing forces
Because the base of the column adjacent to the site boundary cannot spread uniformly around the column it is combined with the base of an adjacent column to form a combined or balanced base foundation.
