Skip to main content

Foundation Type and uses


Foundation of building structure as the name implies is the starting/beginning of a building construction.
When building or planning to build a new home (house) or a structure, it is vital that you get the foundation right or you might find your home.
·        Moving,
·        Cracking, or even
·        Sinking or collapsing over time.

Foundations are that part of walls, piers and columns in direct contact with, and transmitting loads to, the ground. They are sometimes called footings or the substructure in engineering field, and are designed to support the columns, beams, slabs, walls and the roof loads and wind loads in some instance (i.e. sky scrapers) and also to provide a solid base on which to build the house.
Foundation is the structure that transmits the load of the building to the soil. The type of foundation chosen will depend on two distinct variables.
The total building load (dead and live loads),( which means the weight of the house and the load of properties within the house),
. In addition, different weather conditions and soil types may reduce the effectiveness of foundation, depending on the type of soil. Frost heaves (upwards swelling of soil during freezing conditions) is common problem in sandy soils where water in the ground freezes and pushes upwards as it expands into ice (i.e. western continent). The reverse problem is drought, which causes shrinking of the land and is most common in clay soils (i.e. tropical regions). Both conditions can seriously affect the foundations, causing disturbance and, in extreme cases, cracking of the foundations. They are, however, easily avoided if you dig deep enough trenches to around 1 meter or so depending on the designed foundation.
The ratio of water to cement used in the mixing of concrete affects its ultimate strength, if so little water is used the concrete will be so stiff that it cannot be compacted and if too much water is used, the concrete will not develop full strength. Very little water is required to ensure that a full chemical reaction takes place within the concrete mix.


 Foundation types:

1)    Strip foundation –

Strips Foundation 

This is the most common type; it is mainly used where you have strong soil base and non-waterlogged areas. Most small buildings of just a floor are constructed with this type of foundation.
Strip foundation consist of a continuous formed centrally under load bearing walls which serves as a level base on which the wall is built.
 Depends on the structural engineers advice, the depth of your foundation could be from 600mm to 1200mm (2ft to 4ft) mostly for small scale buildings. When the soil is excavated, a level at which the concrete will settle evenly is established, then concrete is poured this may be from 150mm(6”) thick to 450mm(18”) thick depending also on building after that, block is set round the trenches at the center of foundation ,the foundation usually follows the block lines. The blocks are then laid to D.P.C (Damp Proof Course) level before another concrete is poured on top, this is the German or over site concrete. This type seems to be the cheapest.
Forms of strips foundation includes stepping strip foundation, wide strip foundation (reinforced or not), narrow strip foundation,


 2) Pad foundation –

Pad foundation 

Pits are excavated down to the necessary dept level and sides of the excavation may be temporary supported, isolated pads of concrete and columns (pillars) are casted from the bottom of the pits or foundation to carry a slab and beam at the top of the ground.pad foundation are constructed to carry point loads, it transfer the loads to a lower level where soil of sufficient load bearing strata exist. The width can be increased to distribute the loads over a greater area, thus reducing the pressure on the ground.pad are usually reinforced according to design


 3) Raft foundation (Mat foundation)-


Raft/Mat Foundation
Raft foundation consists of a raft or mat of reinforced concrete under the whole building.
This is where you have concrete spread around your building from the base of foundation all through to the German floor/over site concrete/ground floor slab. It is mainly used in areas where the soils is sandy and loose you spend more on this than the other previous two most of  the time. It is also recommended in waterlogged areas but with buildings of fewer storeys it has a ground beam which shuts out from the foundation base and is also attached to the ground floor slab to form a network of concrete embedded round the building space. A raft foundation is a type of foundation that spreads the load around your building or structure from the base of foundation all through to the German floor/oversite concrete/ground floor slab. The concrete can be stiffened by ribs or beams in order to provide extra strength and to help with the distribution of the load. Raft foundations are ideal for use on softer or looser soils as they spread the load so well. They can also be used when a standard strip foundation would cover more than half of the ground area underneath the building, or when there may be movement in the deeper soil levels. Because the raft foundation distributes the load evenly over an area, it will not have areas of pressure that can cause soil settling that will damage the building. A raft foundation is usually laid on a hardcore or scalping bed and the foundation is thickened at the edges. The exterior walls are generally built upon these thickened edges as are the inner walls. The ground beams are usually from 600mm to 1200mm for low buildings.


4) Pile foundation-

Pile foundation
Where the subsoil is of firm, shrinkable clay, which is subjected to volume change due to deep-rooted vegetation and uncertain soil bearing capacity below surface, its advisable to use a system of piles foundation.
Piles are either precast or driven (hammered) into the ground or cast in holes (cast insi tu) that are dilled into the ground down to a level of firm, stable, stratum of subsoil.
Pile foundations are used to support the weight of the building on top of them and also to transfer part of the weight of the building to the surrounding soil. A pile foundation is classified as a deep foundation as the piles (also known as piers) are sunk deep into the soil in order to provide more support and stability. They are used when the soil on which the building stands is soft, silty or clayey. By sinking the foundations down past the softer, less stable surface layers of soil, the foundations can find a strong substrate.
Pile foundation can be classified into short-bored pile foundation and deep foundation
And as Precast or Driven foundation and Cast in holes (Cast insti tu)
The most expensive and the strongest type of foundation, this requires specialist engineering to do.



for foundation concrete mix ratio and grading, see.
concrete grading and mix ratio
Labels:

Comments

Post a Comment

Popular posts from this blog

Construction Procedure of Surface Road Side Drainage-PART 1 (with picture)

Surface water ( i.e., rain water) that falls on the ground surface such as; open field, paved areas or road surface, roof tops etc are channeled to a main drain naturally or through a constructed channel which is referred to as drainage. Procedure for construction of a common drainage (trench) (1m x 1m U drainage) (reinforced). includes; I.       Marking Of Alignment: The surveyor marked out the alignment for the trench to be dug. II.       Digging/Excavation: The surveyor marked out the dept of the trench to be excavated with a mechanical excavating machine. For a 1m x 1m drainage, the mathematical process of obtaining the required dept is to sum together the dept of the required drain + base + blinding. For dept:  A drain of dept1000 mm, base of 150 mm and blinding of 50 mm. Hence 1000mm + 150mm + 50mm = 1200mm (1.2 m) So an excavation of 1200mm (1.2m) is required from the to level of the road surface. For width:
Post a Comment
Read more

Construction Procedure of Surface Road Side Drainage-PART 2 (with picture)

  V.        Next step is laying of concrete base on the blinded surface and the positioned reinforcement. A concrete base of 150 mm is to be laid or cast on the blinded floor, concrete grade C20 of ratio 1:2:4 is allowed (See concrete grading and mix ratio). A guiding panel is placed into position to guild in the laying of the concrete base in order to achieve a uniformly alignment base edge, thickness and width, also to manage concrete material while pouring. The base is cast with the U shape reinforcement bottom in between the concrete base achieving concrete cover below and above.   VI.        After setting and drying of the concrete base, next is to position the side wall panel form work. The floor base is marked to give the required one meter (1000 mm) internal width where the panel will be positioned. The panel wall spacing is 100mm, and wall height of 1000mm (1 meter), the panel is lubricated, clipped and prepared to accept the Concrete.
Post a Comment
Read more

Setting out of a building

A building is set out in order to accurately define the outline and width of the excavation and to determine the center line of the proposed building walls, so that construction according to the building professionals drawing (the architectural plan) plan can be transfer into the ground, this building process is called setting out of building. The center line method of setting out is generally preferred and adopted Setting out can be a very complex engineering process but with need experience its quite easy. Experienced engineer and surveyors are those involved in setting out of structures, in large projects, services of land surveyors are required for more accurate transfer of levels and angles in setting out with the aid of a Theodolite to decided point around the building area But we are going to concern ourselves with the most common setting out method ·          Setting out using pegging ·          Setting out using blocks. But here, we will be discussing
Post a Comment
Read more