Foundation selection based on soil types

FOUNDATION SELECTION BASED ON SOIL TYPES

Foundations are selected based on the type of soil reason being not every foundation can be supported on every soil type because of their varying textures and properties.

Foundations are selected based on the following types of soils: - 

1. Rocks

2. Uniform, firm and stiff clay 

3. Soft clay

4. Peat

1. Rocks: - Rocks, hard sound chalk, sand, and gravel with limited clay content and dense silty sand all fall under this group.

The foundations recommended for this soil type are:

1. Raft foundation

2. Pad foundation

3. Strip foundation

2. Uniform, firm and stiff clay: - This type is divided into 3 cases:

•  If the foundation is adjacent to the vegetation or where the presence of vegetation is unimportant.

The foundations recommended for this case are: -

1. Raft foundation

2. Strip foundation

3. Pad foundation

•  Where there are trees, hedges and bushes near the foundation or where there is a proposal to plant these plants near the structure in the future.

The foundations recommended for this case are: -

1. Concrete piles supporting reinforced concrete ground beams and precast concrete floor.

2. Raft foundation.

3. Specially designed trench fills in certain clay soil based on the foundation location relative to trees. 

4. Concrete piles carrying in situ concrete slab.

• Where trees are felled just prior to the start of foundation construction

The foundations recommended for this case are: -

1. Strip foundation

2. Raft foundation

3. Reinforced concrete pile in previously tree root zone

3. Soft Clay: - soft clay, soft silty clay, soft sandy clay and soft silty sand all fall within this group. 

The foundations recommended for this case are: -

1. Pile to firmer strata below

2. Wide strip footing

3. Raft foundation

4. For smaller projects use pier and beam foundation to firm strata.

4. Peat: - The foundations recommended for this case are as follows:

1. Raft foundation for the case where firm strata is not available at reasonable depth but there is hard surface crust within 3-4mm thick of suitable bearing capacity.

2. Concrete piles extended to the firm soil layer below.

3. For small projects, pad and beam foundation are taken to the firm strata below.