We can distinguish three main types of foundation which are:
- the surface foundation
- the deep foundation
- the special foundation
A structure, whatever its form and destination, is supported on a seat floor and transmits a set of loads to it.
The elements which play the role of interface between the supporting structure and the ground constitute the foundations .
Adapted to both the structure and the nature of the soil, they take various forms so as to ensure a good distribution of stresses. We distinguish the following different types of foundation :
- Continuous soles under the wall.
- Insoles insulated under pillars.
- Plots and sills.
2-Foundation by deleting general.
- On well.
- On stakes.
1- SURFACE FOUNDATIONS:
Shallow foundations (i.e. shallow foundations ) are used when:
- The soil capable of the necessary lift is at depth.
- The shear resistance of the layers is sufficient.
- The deformability of the soil is low.
This process is economical in the case where the bearing soil is accessible by common earthmoving means, that is to say for depths between 1 m and 4 m at most.
The surface foundations consist of footings having a greater width than the supported element so that the compression ratio of the soil does not exceed its admissible compression ratio.
1-1 Continuous footings under the wall:
Wall foundations can be made:
- In masonry.
- In rubble.
- Reinforced concrete.
- Reinforced concrete.
A- Brick foundations:
- At the end of the trench, we lay a first layer of bricks on a layer of coarse sand.
- Over this entire width of the bass we build at least 2 seats.
- We then gradually shrink each set of two seats until the desired thickness or wall is obtained.
- The tangent to the overlaps cannot be tilted by more than 60 ° with respect to the horizontal.
- What exceeds the 60 ° angle undergoes tensile forces: masonry of broques cannot resist it.
B- Rubble foundations:
Rubble foundations generally fill the entire width of the excavation.
- At the bottom of the trench we put a layer of clean concrete.
- Then put a layer of mortar 3 to 4 cm thick and then place the rubble, blocking it and bonding it properly with mortar.
C- Grained concrete foundations:
The cross-section of the groomed concrete foundation in the form of an isosceles trapezoid whose
bass angles are at least 60 °.
Concrete can be cased or poured directly between the two walls of the excavation. It must be of “wet earth” consistency and carefully groomed during installation.
This concrete is sometimes lightly reinforced to form a chain which may be necessary if the soil is not homogeneous.
D- Reinforced concrete foundations:
We use reinforced concrete footings :
- To distribute the load more evenly (consequence of their greater rigidity).
- To limit the weight of foundations ( stronger foundations therefore less thick).
- To reduce the pressure exerted on the ground by widening the sole (which requires a reinforcement to resist the tensile forces produced at the bottom of the sole ).
First, a lean concrete of concrete 5 to 10 cm thick is poured. We then pour the reinforced concrete footing either between floors
forming formwork, either directly between the walls of the excavation.
1-2 Insoles insulated under pillar:
These pyramid or rectangular footings can be made of concrete or, more often, reinforced concrete.
The tensile forces due to the bending of the sole are manifested in 2 perpendicular directions according to these efforts involves the installation of a reinforcement along these 2 axes. This reinforcement therefore a grid.
Concrete must be heavily packed and vibrated. It is generally poured between the earth walls, prepared at the time of earthwork, at the required dimensions. Previously, the reinforcement was placed on a form of about 5 cm thick, made of lean concrete and forming clean concrete.
The upper side of the sole, intended to receive the formwork of the pillar, must be provided with a redent of about 5 cm.
The connection of the sole to the pillar is ensured by a waiting reinforcement included in the reinforcement of the foundations .
1-3 foundation by prefabricated studs and sills:
A concrete stud is a massive square or rectangular footing , made of coarse concrete , unreinforced or lightly reinforced.
A sill is a reinforced concrete beam that serves as the foundation for the walls.
The foundations by studs and prefabricated sills are formed by a load-bearing assembly consisting of:
- Isolated support points on the foundation soil (the studs).
- Longrines which come to rest on the studs
The sills carry the walls and serve as chaining at the Foundation level . They can also be used:
- Either to support the floor.
- Or limit the paving on the banks of the building.
This system is frequently used, especially on construction sites with a large number of similar dwellings.
The sills are then prefabricated in series to the desired lengths.
This system has the following advantages:
- Minimum earthworks (only for the studs).
2- GENERAL RADIER:
The general raft is in the form of a foundation p p which transmits the loads of the construction on the ground by an area equal to or greater than that of the structure.
It can be made up of:
- Either by a simple thick slab.
- Either by longitudinal and transverse beams linking the supporting pillars and supporting a thinner slab.
This solution can be adopted:
- when the soil is not very resistant but homogeneous.
- when the construction area is small in relation to its height or weight (skyscrapers, silos, etc.).
- when you want to get a waterproof basement for a construction sitting in an underground water table.
3- DEEP FOUNDATIONS:
When the good soil is several meters deep it would be
too expensive to descend conventional foundations to the desired depth because:
- The volume of soil to be removed.
- Shoring to be put in place.
- Difficulty carrying out such searches.
The load is then transferred to the correct floor by separate support points. There are two processes:
3-1- the wells
– “Wells”: we dig “wells” of at least 1 m in diameter to the right soil and fill them with unreinforced concrete which serves as a foundation .
3-2- the stakes
– “Piles”: reinforced concrete elements with a diameter of +/- 40 cm and a length of up to more than 20 m can be driven into the ground if necessary.
Longers connecting at the head these piles or these wells provide the masonry with a stable and flat foundation.
The study of deep foundations is the responsibility of the engineer and is carried out in collaboration with specialized firms, following tests.
The following drawing shows the drilling steps.