Strip Foundation
The strip footing is the most common foundation for masonry structures, and is wider than the masonry above it.
It is typically made of concrete or floating concrete, poured between the foundation trench walls.
If the soil is not of sufficient strength, formwork is required for its construction.
If structural reinforcement is required, scaled reinforcement is also placed in the concrete.
The implementation process is as follows:
- Site clearing to remove plants and humus, the top layer of soil.
- The batter boards are installed, fixing all the corner points and the boundary lines, which can be marked out on the surface of the soil, for example with lime powder.
- Dig the foundation trenches, either by machine or by hand, taking care to ensure that the levels are at the correct height.
- Formwork - only if necessary. In this case the foundation trench should be made wide enough to accommodate the formwork.
- A blinding layer is prepared for the steel fixing.
- Concreting takes place using a rotating drum mixer or by pouring ready-mixed concrete, in layers of approximately 25 centimetres.
The layers must be compacted with a rod vibrator.
During solidification, the concrete must be watered to avoid rapid loss of moisture, which could lead to the concrete overheating.
- Removal of formwork.
- Backfilling in layers of 15 cm and compaction around the foundation.
The foundations of the partition walls are made in the same way as the main walls, but with a smaller cross-section.
The cross-section can be further reduced by using reinforced beams.
For light loads, it may be sufficient to reinforce the substrate with reinforcing steel.
In the case of sloping terrain and the use of different foundation levels, the strip foundation must be stepped.
The maximum level difference (step height) is 50 cm, and the maximum angle of inclination for the stepping is 30 degrees.
Spread Footings
Spread footings support columns or pillars and are typically made of monolithic reinforced concrete.
Spread footing can also be a prefabricated reinforced concrete structure, a so-called pocket foundation.
Constructing monolithic reinforced concrete is the same as for strip footings, except that the footings are isolated and not continuous.
When they are constructed, the longitudinal rebars of the pillar typically continues into the foundation to create a fixed joint.
Waterproofing can be also accomplished by placing metal sheeting under the pillar, or by insulating around the entire spread foundation.
For pocket foundations, the typical solution is to first construct the monolithic concrete spread foundations and then place the pocket foundations on top of these.
The placement requires 8 to 10 cm of blinding concrete on top of the pad footing and then placing the pocket foundation in the bedding mortar laid on its surface.
The pillar is then lifted into the pocket, initially fixing it with wedges and finally concrete.
Waterproofing can be achieved with a pillar made of watertight concrete.
Strap and Grid Foundation
This may be necessary if the load is too heavy, resulting in point bases that are too large or too close together.
Also, it may be necessary where there is a risk of subsidence or slipping.
The construction is the same as for a strip foundation.
Mat Foundation
A mat foundation is particularly needed in poor bearing soils, but most of all in high groundwater.
The mat foundation resists the water pressure through its weight and its uniform design, which provides protection against flotation.
Construction of the mat foundation:
- After site clearing and setting out, drainage follows.
- After the excavation work make a min. 10 cm thick insulation protector concrete substrate, on which the waterproofing layers are laid.
The substrate is wider than the mat in all directions and is provided with a perimeter beam to receive the insulation retaining wall, which can be built from small bricks, for example.
- Complete the ground waterproofing arouind the entire mat foundation.
- Lay 5 cm of blinding concrete, and follow with any necessary formwork and ironwork.
- Complete the concreting, preferably in one session.
- Finally, the earth is backfilled.
