Typical strip foundations are a continuous strip of concrete supporting load-bearing walls.
Deep strip foundations:In instances where strip foundations are required to be at a lower level to reach soil with suitable a bearing capacity, a wider, deeper trench can be dug to work in. The strip foundations are then dug and poured at a lower level. Walls are then built up to ground level in masonry.
Wide strip foundations: In instances where the soil is soft or of a low load-bearing capacity, wide strip foundations can be used to spread the load over a larger area, reinforced with steel so that the loading per m² is reduced.
Typical Pad foundations are used to support individual or multiple columns, spreading the load to the ground below. They are generally square or rectangular in plan, with the plan area being determined by the agreed bearing pressure of the soil. The shape in plan will be dictated by the arrangement of the columns and the load to be transferred into the soil.
The thickness of the slab must be sufficient to ensure distribution of the load. The top of the pad may be sloping (i.e. the pad is thicker in the centre than it is at the edge). This is an economic solution, although there may be construction problems involved with casting the slope.
Typical reinforced concrete raft foundations are used on very weak or expansive soils such as clays or peat. They allow the building to ‘float’ on or in the soil. Raft foundations are used where the soil requires such a large bearing area that wide strip foundation would have to spread too far. The Raft foundation offers a economical than pouring slarge reinforced concrete slab. A raft is an alternative to piles as it can be less expensive.
Due to ever increasing high cost of labour, deep strip foundations are more commanly being replaced by trench fill foundations. Typicaly trench fill foundations are dug to a depth where the subsoil provides sufficient load-bearing capacity, the entire trench is then filled with concrete. Steel reinforcement may be added in areas close to trees.
Compared to a deep strip foundation, trench filled foundations minimise the width of the dig and in turn the labour costs and as a result the materials required for building masonry below ground level, offsetting the cost of the additional concrete.