Role of Structural Design Consultants in Foundation Design

What is a foundation?

The foundation is a critical part of any building or non-building structure. Industrial structural consultants understand that foundations help transfer the load from the structure to the ground.

The foundation bed is the ground on which the foundation rests. The foundation depth is the distance from the natural ground level to the lowest part of the foundation. 

Is foundation essential for the structure? 

The foundation of a structure helps in the following: 

1. The foundation helps distribute the structure's weight over a large soil area.
2. It helps avoid unequal settlement.
3. Lateral movements are restricted due to foundations.
4. Foundations help increase structural stability by anchoring the structure to the ground.
5. Foundations form a level surface for construction.

These are some reasons foundations are an essential element in any structure. 

What are the characteristics of a good foundation? 

A well-designed, constructed, and performing foundation has the following characteristics:

1. The design and construction ensure the foundation sustains and transmits the load to the ground. The transfer of load doesn't result in settlement.
2. There are no differential settlements, especially where the superimposed loads are not uniform.
3. The temperature changes also do not cause shrinkage and swelling. 
4. The foundation location is in an area with no chance of disturbance due to future work.
   

Footing types

There are two kinds of foundations depending on their depth- shallow and deep. The structural consultants design different foundations depending on the soil type, the bearing capacity of the soil, and the structural loads. 

Shallow Foundations

Shallow foundations are economical because of the depth. It is typically for structures that are lightweight. Shallow foundations are of the following types:

1. Isolated Spread Footing: These footings transfer the load of the columns to the soil. They are economical. These foundations typically are rectangular, square, or round. Reinforcement is as suggested by the structural design consultant. These foundations are common when the structural load is low, and soil bearing capacity is high at a shallow depth. 
2. Strip footing: Strip footing, also known as continuous footing, distributes the structural loads. Structural consultants design strip footing when loads are small and the soil is dense. 
3. Combined Footing: These footings overlap each other and form part of the structure. They are typically used with soil of low bearing capacity. Foundations are often common to multiple columns and help in a uniform load distribution. These foundations are economical when placed too closely or a footing on one side has restricted dimensions.  
4. Strap Footing: These are similar to combined footings with the foundations under the columns individually built and a strap connecting them. Structural consultants use this type of footing to extend the footing's edge beyond the property line. A strap beam connects the exterior footing.
5. Raft or mat foundations: It's used when other types of foundations are not recommended or when the soil-bearing capacity is inadequate. Structural consultants usually design these types of foundations when the structural load distribution is spread over a large area, or when the structure is subjected to continuous jerks and shocks. These types of foundations are also effective in preventing differential settlement. 
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Deep Foundations

There are several types of deep foundations. Some of the common types of deep foundations are as follows: 

1. Pile Foundation: Pile foundation is a common type of deep foundation. Pile reduces the cost and transfers the loads to deeper soil or rocks. This foundation helps resist uplift by the structures and lateral forces. Some factors for selecting this type of foundation is: 
1. The soil at a depth has great bearing capacity.
2. Irrigation canals in the vicinity.
3. Raft Foundation is expensive.
4. There are concentrated heavy loads on the foundation. 
5. Marshy areas
2. Pier Foundation: Piers are shallower than piles, and consultants design pier foundations for multi-storey structures. They go for pier foundations in situations like: 
1. A rock strata is under a decomposed rock layer at the top.
2. Topsoil is not suitable for piling.
3. Heavy load to be transferred to the ground.
3. Cassion Foundation: This type of water-tight retaining structure is for bridges or structures that need a foundation beneath a water body. 

Foundation and Soil Types 

Structural design consultants decide on the type of foundation based on the geotechnical analysis of the soil. Foundations are an essential and critical part of a structure. Structural consultants must give the necessary thought before designing.