The Constructor

Selection of Foundations Based on Different Types of Soil

selection of foundations based on different types of soil

Commonly, the selection of foundation type for a given structure is controlled by number of factors for example soil type, past site usage, adjacent construction, size of development process, limitations.

Among these factors, types of soil play significant role, that why this article discuss the selection of foundation based on different types of soil.

Selection of foundation based on different types of soil

Foundations are recommended based on the different soil types which are provided below:

  1. Rocks
  2. Uniform firm and stiff clay
  3. Soft clay
  4. Peat

1. Rocks

This category involves rocks, hard sound chalk, sand and gravel, sand and gravel with little clay content, and dense silty sand.

Recommended foundation types

The following types of foundations are suitable for this type of soil:

  1. Strip foundation
  2. Pad foundation
  3. Raft foundation.

Fig. 1: strip footing

Fig. 2:pad foundation

Fig.3:Raft foundation

Factors need to be considered

The following factors shall be taken into account while foundation type is selected:

2. Uniform firm and stiff clay

There are three cases which are discussed below:

Case I

where the foundation is not close to vegetation or existing vegetation is not important.

Recommended foundations

  1. Strip foundation
  2. Pad foundation
  3. raft foundation.

Factors to be considered in this case are as follow:

Case II

where trees, hedges, and shrubs are close to foundation location, or there is a plan to plant these trees near the structure in the future.

Recommended foundation

One of the following types of foundation may be selected:

  1. concrete piles supporting reinforced concrete ground beams and precast concrete floor
  2. concrete piles carrying in situ concrete slab
  3. specially designed trench fills in certain clay soil based on the foundation location relative to trees
  4. Raft foundation

Fig.4:pile foundation

Factors to be considered

Case III

where trees are cut down shortly before the foundation construction begin

Recommended foundation

  1. Reinforced concrete pile in previously tree root zone
  2. Strip foundation
  3. Raft foundation

Factor needed to be taken into accounted

3. Soft clay

This category includes soft clay, soft silty clay, soft sandy clay, and soft silty sand.

Recommended foundations

The following types of foundations are valid option for this type of soil:

  1. Wide strip footing
  2. Raft foundation
  3. Pile to firmer strata below
  4. For smaller projects use pier and beam foundation to firm strata

Factors to be considered

4. Peat

Recommended foundation

  1. Concrete piles extended to the firm soil layer below
  2. For small projects, pad and beam foundation taken to firm strata blow.
  3. Raft foundation for the case where firm strata is not available at reasonable depth but there is hard surface crust with 3-4m thick of suitable bearing capacity.

Factor to be considered

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