Foundation 283

foundation is a base at which a building rests and its use is to transfer the weight of a building to a suitable sub-soil.

soil in building code is classified as:-

  1. clay
  2. silt
  3. gravel
  4. rock
  5. black cotton soil

types of foundation

strip foundation – has a trench equal to the wall of foundation with a concrete strip cast at the bottom.


stepped foundation – used in a place where the land is not level to reduce excavation.


pad foundation – in this each column has its own isolated base where the load is transmitted to.

raft foundation – this is found where the soils have no bearing capacity or where there are different types of soil with different bearing capacities.


deep strip foundation – it is constructed underneath all walls of the ground floor and is used in small buildings or where minimal excavation is to be carried out.

excavation – this is the cutting, digging or scooping of land to form a trench.


This is the temporary support to the sides of excavations.

Types of timbering

hard soils timbering – This is used in soils that are hard. it resists collapse of soil on the workmen on the trench. its dug by a trencher, a excavator or a backhoe if its a mechanical method. it can also be dug by fork, spade or mattock if its manual. 

loose dry soils – this are soils that are loose yet dry. they tend to collapse a lot  so walling and polling boards are used to prevent collapse. the strut is there to provide support.


loose wet soils – this is used in soils that are loose yet wet. this are very dangerous soils left without plunking and struting i.e timbering. They are to be supported with walling and polling boards and a strut to support the boards.

Walling boards are the longitudinal timber boards while polling boards are the vertical polling boards. struts are the members joining the two parallel walling and polling boards.


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