How To Build A Raft Foundation In Silty Soils
Silty soils are unstable and have very low safe bearing capacity. This means that they cannot safely carry foundations. Due to there unstable nature, different foundations are used. This foundations are either piles or rafts. The raft foundation involves bulk excavations. Other soils that may require total bulk excavations are cotton soils. The excavations allow for the loose silt to be removed. This is normally found on areas near water bodies, rivers, bottoms of valleys and swamps. The depth will vary according to the topography of the land.
Raft foundations cover the entire area of the building. This means that the total surface to be covered is built on this foundation. The depth of excavation should be determined on site. The foundation should be cast on a firm surface. This is usually a hardcore surface. The depth of concrete is one foot over general surfaces. to be located, the depth is one and a half feet. The whole base should be like a floating mass of reinforced concrete.
The raft foundation commences by marking out the desired building layout. After checking the depth of silt from a trial pit., excavation commences. After it is complete, a compactor is used to form a flat hard surface. Care should be taken to avoid water in the pit. The firm surface is then compacted to the approved levels. When this is complete, Hardcore is then added to the pit. This is compacted in stages of one foot. A two feet depth is ideal.
After the hardcore is in place, The areas to have the walls are marked out. Any walls that are load bearing are clearly marked out. Hardcore is then removed to a depth of one foot and two feet wide. Blinding and a damp proof membrane are laid over hardcore. A mesh reinforcement is laid over at a height of six inches. Concrete is then poured onto the hardcore. After curing for a week, the walling may now commence for the actual building.