raftAuthor: Andrew Karundu: 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

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