27/01/2018
If you are intending to build a home you have to understand the basics of what going to be happening when we build your home
Today lets talk about Foundations
The foundations of the building transfer the weight of the building to the ground. While 'foundation' is a general word, normally, every building has a number of individual foundations. Most buildings have some kind of foundation structure directly below every major column, so as to transfer the column loads directly to the ground.
Since the weight of the building rests on the soil (or rock), engineers have to study the properties of the soil very carefully to ensure that it can carry the loads imposed by the building. It is common for engineers to determine the safe bearing capacity of the soil after such study. As the name suggests, this is the amount of weight per unit area the soil can bear. For example, the safe bearing capacity(SBC) at a location could be 20 T/m2, or tonnes per square metre. This figure is the maximum the soil can bear, so an engineer will take pains to see that her design does not exceed this figure in any part of the building.
This capacity also changes at different depths of soil. In general, the deeper one digs, the greater the SBC, unless there are pockets of weak soil in the earth. To properly support a building, the soil must be very firm and strong. It is common for the soil near the surface of the earth to be loose and weak. If a building is rested on this soil, it will sink into the earth like a ship in water. Building contractors will usually dig until they reach very firm, strong, soil that cannot be dug up easily before constructing a foundation.
To study the properties of the soil before designing foundations, engineers will ask for a soil investigation to be done. A soil investigation engineer will drill a 4" or 6" hollow pipe into the ground, and will remove samples of the earth while doing so. He will then send these samples to a lab to find out the detailed properties of the soil at every depth. Soil is usually composed of strata, or different layers, each with its own set of properties. Drilling technology today makes it easy and economical to drill to great depths, easily several hundred metres or more, even in hard rock.
The soil investigation team will then prepare a soil investigation report that lists the engineering properties of the soil at regular intervals, say every 2 meters. Based on this deport, engineers designing the structure can decide at what depth of soil to provide the foundations, the type of foundations they should provide, and the size of the foundations.
Once the foundations have been built, the loose soil that has been excavated must be put back over and around the foundations. This is called backfilling. Backfilling must be done carefully, as the soil there must support the weight of the floor slab at ground level Backfilling is done by putting back the soil in horizontal layers about a foot thick, and then compacting the earth, or squeezing it under pressure in a wet condition. This causes the soil particles to be squished together and removes air voids, there by making the layers strong. Good backfilling also improves the performance of the foundations, as the earth holds them firmly in place, and weighs down on the foundations to anchor them in position.
(BuildersUnderstandConstruction)
Have you learnt anything new?
