The purpose of the foundation can be neatly summed up with the following goals:

  • To evenly distribute the building’s weight load across the foundation bed.
  • Avoiding unequal settlement (making sure the building is, and stays level).
  • To prevent sliding/sideways movement.
  • Increasing building stability and structural fortitude.

Main types of foundation and their selection

The main types of a building foundation can be put into two categories: deep foundation, and shallow foundation. Ultimately, an construction contractor and/or engineer will choose the foundation type based on:

Although the criteria for foundation building can be complicated, a foundation is generally judged as shallow if the width of the foundation is greater than the depth at which it is placed. The foundation will be a deep foundation if the depth at which it is placed is greater than its width.

Shallow foundation types

Wall/continuous/strip footing

This foundation types spread continuously beneath the wall, and transfer the load directly from the wall into the ground. The footing should be two to three times the width of the wall at floor level. It can be made of many types of materials too, including stone, brick, reinforced concrete, or plain concrete cement.

Wall footing is best used when:

  • The building has a light load. (It’s good for houses ans small residential structures)
  • The soil is dense sand or gravel.

Isolated or pad-spread footing

We will try to define important foundation-related terms as we get to them, so knowing what footing is is important. Footing is the actual part of the foundation that spreads the load to the soil (foundation bed) beneath it. In general, it is a concrete square – or foot – that does this. 

This is lower-cost and effective shallow foundation option. It uses spread out columns, often reinforced, with cement feet at the bottom contacting the foundation bed. Each section/column has its footing, which may be rectangular, square, or circular. 

Isolated spread footing is best used when:

  • The structure has a relatively low load.
  • The soil has a high bearing capacity, even at a shallow depth.
  • The columns/sections are far apart from one another.

Combined footing

This type of foundation is made wider by providing rows of columns. It is a footing type which is quite similar to isolated footing. However, it uses a blend of different types of footings according to the requirements of the structure, and the footings can be many different shapes. There are different types of combined footing, but ultimately, what makes combined footing is that individual footings act as one.

Combined footing is a good choice under the following conditions:

  • The columns are constructed close to each other.
  • Dimensions of one side of the footing are restricted, necessitating a trapezoidal or other non-rectangular or circular shape.
  • When a footing from a column may cross a building’s property line, requiring a different or eccentric shape to still distribute the load.

Cantilever/strap footing

This is an even more specific type of combined footing, used in cases when the footing can not extend beyond the property line. It is when other footings are combined using a strap beam (a beam at soil level that unites the footings).

Mat/raft/fleet foundation

This is constructed via a joining notch which covers the entire foundation of the structure, receiving load from both walls and columns. It is made of reinforced slab, or T-beam slab. The name comes from the foundation spreading the total load evenly, acting almost like a raft for the building, while the soil is the water.

Use mat foundation when:

  • Weak soil requires a large load spread.
  • Columns are close to one another.
  • The structure is often subjected to shocks.
  • You need to use a shallow foundation with a heavy structure.
  • The building has a basement.

Deep foundation types

A pile is a thin, long cross-sectional material, planted deep in the earth and used for transmitting the structure’s load to various strata of soil. There are many types of piles, but they all ultimately use their length and depth to transfer load. Piles can be made from timber, concrete, steel, and composite.

When to use pile foundations:

  • Soil with higher bearing capacity is deeper. The load can be shifted to a stronger strata, such as rock.
  • When there is a heavy concentrated load.
  • In marshes, riverbeds, and where top soil strata are more compressible.
  • When other foundation types are too expensive.

Caisson foundation

Caisson is a water-tight foundation type used for structures that will be placed in bodies of water. It is  used because the foundation structure can be built, floated into place, and then sunk to the bottom of the water body. They are made from hollow tubes sunk into the soil and then filled with concrete to transform into a foundation. 

Use caisson foundation for:

  • Piers, dams, bridges, and other structures on bodies of water.
  • High loading capacity is required.
  • Vibration and movement should be kept to a minimum. 
  • The least pile is required.

Pier foundation

This transmits a much larger load that shallow foundation types can not carry. It consists of large cylindrical columns that transfer the structure loads to the strata beneath. The pier cylinder will have a pile cap at its bottom end, which multiple piles stick out of and delve into the soil.

Used when:

  • Solid rock strata lie beneath damaged rock.
  • Stiff clay soil resists driving piles.
  • A heavy load must be transferred to the soil.

Start your building off with the right foundation

Figuring out what foundation to use is no easy task. With so much to choose from, it’s hard to know what the best fit is. So why not leave it up to the professional commercial contractors? Reliable Commercial Construction can figure out what foundation is right for you. Message us today to get started.