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Introduction

In the past 20 years, thousands of foundations in building construction have collapsed all around the world due to failures alone. As a construction site manager, I have witnessed a few collapses and I am willing to share all I know about the concept of foundations in building construction and the causes of foundation collapse.

foundations in building construction

After reading this post, you will be able to avoid foundation collapse which can be disastrous and lead to loss of lives and leave many injured.

 

History and concept of foundations in building construction

The concept of foundations in building construction is an important one to understand because a good foundation will help a building stand up to the elements, keep its structure intact, and ensure that it can be used for many years to come.

The Foundation of a structure is always constructed below the ground level so as to increase the lateral stability of the structure. It includes the portion of the structure below the ground level and is built, so as to provide a firm and level surface for transmitting the load of the structure on a large area of the soil lying underneath. The solid ground on which the foundation rests is called the Foundation Bed.

foundations in building construction
source: thespruce.com

A properly designed foundation will also be able to resist movement, provide drainage and ventilation, and support the surrounding infrastructure. Foundation work should be carried out by a qualified
professional, in order to ensure that the building is protected and that its long-term stability is ensured.

Foundation meaning in construction

A good foundation will be composed of a solid base layer It should be supported by surrounding layers that provide stability and support The foundation should be designed to accommodate the weight of the building above it and the loads it will be subjected to, It should be able to withstand the expected and non-expected environmental conditions (natural or man-made) like an earthquake, whirlwind, adjoining demolition, etc, therefore, from the above:

A foundation can be defined as the structural system that is below the ground which gives support to the superstructure by transmitting its loads directly to the earth through other structural elements.

Purpose/ uses of foundations in building construction

  • Stability is the major or main purpose of a structure. Foundations are built mainly for this. The stronger the foundation, the more stable the structure becomes.
  • Foundations are designed so that a proper firm flat surface bed can be constructed for the development of the substructure ready to receive the substructure.
  • Foundations ensure that lateral movements are avoided when such foundations are specially designed.
  • Another purpose of the foundation is the receipt, into the ground, of uniformly distributed load. This uniform transmission aids in preventing uneven building settling. Which causes the foundation to collapse.

The major categories/ types of foundations in building construction

There are different types of foundation designs but they all serve one singular purpose:  to transfer a structure’s weight load to the soil beneath it. The type of foundation of a building is mostly determined by the following:

   the type of construction

   the nature of the soil

   the surrounding environment.

Generally, all types of foundations are categorized into two:     

1.   shallow foundations

2.   Deep foundations

In this post, we will be concentrating on shallow foundations as we have written extensively on deep foundations. You can learn more about it here.

Shallow Foundations

This type of foundation is also called the spread foundation and it is typically suitable where the loads imposed by a structure are smaller than the bearing capability of the surface soils. This load and bearing
the structural Engineer can determine capacity.

Shallow foundations in building construction are constructed with concrete strips that are laid beneath the soil. The depth at which the concrete strip is laid is determined by the bearing capacity of the soil but mostly it is laid about one meter (about 3.28 feet)

Below are the different types of shallow foundations:

a. individual footings/ isolated footing

foundations in building construction

The most frequently used and most economical type of foundation utilized for building construction is the individual footing or isolated footing. This foundation, also known as a pad foundation, is designed for a single column. Individual footings are square or rectangle in shape and are utilized to carry loads from the structure to the ground by the columns.

Generally, every section of the foundation has its own footing which can
be square or rectangular in shape. It can even be circular sometimes.

b.     spread footings

Spread footings are typically utilized to support each structural column.
Construction of these footings is both cost-effective and economical. It works
well on any soil with sufficient load-bearing capacity.

c.      strip footings

foundations in building construction
source: acivilengineer.com

A strip foundation is a continuous concrete that is constructed or cast
centrally beneath the loadbearing walls on the entire proposed building to form
a strip. The continuous strip serves as a support for the walls and is of
sufficient width to distribute the building’s load evenly on the ground beneath
it. This serves as a support for the building.

Generally, the thickness of a strip foundation should not be less than 150mm
and the spread should not be less than three times the size of the proposed
load-bearing wall or more. This minimum thickness is required to ensure that
the strip foundation has sufficient rigidity and can therefore span throughout weak
soil pockets.

Types of strip foundation

The three types of strip foundation are:

  • deep strip
  •  raft
  • trench fill and piled

d.     Combined footings

foundations in building construction

Combined footings are built when two or more columns are near to each other and their foundations overlap. You might be asking “when do you need a combined footing?” A combined footing is necessary when two or more columns are so close to each other and their footings overlap.
This will bring about their footings to be combined into one singular footing to serve two or more columns.

 e. Raft or mat footings

foundations in building construction

A raft or mat foundation is a big continuous rectangular or circular concrete slab that carries and distributes the entire load of the superstructure over the entire area beneath the building. It is one sort of
the shallow foundation that is useful for controlling differential settlement.

Raft or mat foundations are used in foundations when other types of shallow foundations are not suitable or where pile foundations cannot be employed. It is also recommended in circumstances when the soil’s bearing capacity is insufficient.

f.       strap or cantilever footings

picture of strap foundation

A strap footing is a conjunctive feature used with columns that run parallel to the property or plotline of a structure. It connects an eccentrically loaded column to a column well inside the foundation region, allowing the eccentricity’s moment to be transmitted to the inner columnar foot.

g.      grillage foundation

pix showing grillage foundatiomn
source: gharpedia.com

A grillage foundation is a foundation that consists of two, three, or more cross-timbering or metal beams, laid at 90-degree angles, in order to distribute the load over a large area, forming a foundation for building on difficult ground.

Grillage Foundation design is usually applied for heavy structural loads from columns, piers, or beams which are required to transfer the bearing capacity of a soil that is comparatively poor.

Types of grillage foundation:
  1. steel grillage foundationas the name implies, this is an arrangement of steel beams in single or double layers
  2. timber grillage foundation – The timber grillage foundation is mostly used for masonry walls that are carrying an extreme load with timber columns. This type of foundation is especially useful in areas that are covered with flood or where the load-bearing capacity of the soil is very low or is limited to 50-60 KN/M2.
  3. Reinforced concrete grillage foundation – This type of foundation is very typical of the steel and timber grillage foundation. The only and major difference is the type of material used. Steel is used in this instance. But the process remains the same.

Deep foundations

A deep foundation, in construction, is a type of foundation that is… continue reading…

Types and Causes of foundation failure with their remedies

foundation failure depend on a number of different reasons. we will examine the types, the causes, and their remedial solution.

when building construction is to proceed, it is the duty of the civil or structural engineer to carry out necessary tests on the soil to ascertain the bearing capacity of the soil in order to calculate the best suitable type of foundation for the proposed structure.

The following are the different types of foundations failure in building construction:

A.) Foundation failure due to the movement of soil

foundation settlement
original source: theconstructor.org

– water is an important factor In the construction process therefore when the water between soil particles in the foundation *whether from construction works or from nature) is eliminated, the soil particles tend to move closer together. this will cause particles movement due to this space. Clayey soils move around more than sandy soils. This form of soil movement caused by variations in water content has an impact on foundation settling. The foundation has a tendency to settle, and significant foundation settlement can cause structural damage and differential settling.

Soil movement can be caused by one or all of the following factors:

  1. remains of roots or vegetation in the foundation
  2. if the area was mined before
  3. if the soil has a shrinking capacity

Remedial solution for foundation failure due to soil movement:

a. Any mining region should be explored, and professional help should be obtained before building new structures there.

b. Proper elimination of vegetation and/or roots on the construction site

c. Pile foundations should be utilized to transfer stresses to the hard strata or rock when the soil is shrinkable.
d. Lower the foundation levels to avoid foundation on shrinkable soils.

B.) Foundation failure due to Settlement when Soil is Filled

foundation soil settlement
original source: theconstructor.org

There is every tendency that soil will settle if the structure was newly constructed on made-up or imported soil material because such soils take a long time to settle and compress.

foundations on such soils tend to continually settle over time.

The remedial solution to this kind of foundation failure is as follows:

  1. Before building begins on such soils, it must be guaranteed that they are suitably compacted.
  2. The soil should be allowed to settle for a while and properly vibrated with mechanical equipment
  3. The foundation depth should be extended to the hard stratum or rock beneath or under the soil
  4. Pile foundations should be employed.

C.) Foundation failure due to trees and shrubs

foundation trees and shrubs

The trees in the vicinity of the construction site live by absorbing water from the soil, causing voids in the foundation and eventually leading the structure to sink and crack.

The remedial solution to this kind of foundation failure is as follows:

  1. The foundation depth for this kind of foundation failure should be kept at least one meter.
  2. Trees and plants or flowers that have roots that spread should not be planted within 8 meters of the wall.

D.) foundation failure due to load carried by foundation

foundation load
source: gharpedia.org

When this isn’t properly done and a foundation is designed poorly to carry a load is not designed for, one of the following three types of foundation failures under load may occur:

  • Punching shear failure – this kind of failure, which is also called the diagonal tension failure of foundation, happens when there is a formation of inclined crack(s) at the surrounding of the foundation columns probably due to the poor concrete mix or inadequate reinforcements. 

The remedial solution to this kind of foundation failure is as follows:

  1. additional reinforcement should be provided around the column perimeter in order to resist the punching shear.
  2. the perimeter of the column should be properly filled with concrete. It should be properly vibrated with a good concrete vibrator machine with a good concrete compaction test result.
  3. For the given percentage of concrete, the ultimate upward shear force at the critical section of the foundation must be calculated to be less than the shear resistance of concrete. Punching shear failure occurs at d/2 from the column’s face, where d is the effective depth of footing.
  • One-way shear failure – This kind of failure occurs in inclined cracks across the entire width of the foundation footing that intersects the bottom of the footing slab at a distance d from the column face i.e. the critical section, where d is the effective depth of the footing slab.

The remedial solution to this kind of foundation failure is as follows:

  1. The shear stress at the crucial portion of the footing should be made less ess than the shear strength of concrete. A specific percentage of reinforcement should be introduced to avoid the one-way shear collapse of foundations.
  • Flexure failure of foundation – Mu/bd2 is measured during footing design to determine the percentage of reinforcement for the moment the foundation is exposed to.
    The ultimate or calculated moment is Mu, and the breadth of the footing is b.

Other causes of foundation failure?

  • uneven settlement in Soil.
  • Masonry settling is uneven.
  • Moisture movement in the subsoil.
  • Lateral pressure from the superstructure.
  • Atmospheric action. 

 

In conclusion

When choosing a proper type of foundation, the soil type, and the load-bearing capacity of the structure are two of the most important aspects to consider. Regardless of the size of the project, an engineer must be fully aware of the site and its surroundings in order to construct a long-lasting structure without danger of loss of lives and property.
If you’re an engineer, there are a few procedures you must do in choosing the right type of foundation.

Did I miss anything important? Please,  let me know in the comment section below and share this piece if you gained value.

you might also like:

Builders’ mistakes in construction: silly and hard to avoid
Shoring and underpinning in construction: overcome site risks
Different types of deep foundations: what you need to know

featured image: Designed by macrovector / Freepik

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