Foundation and structural design consultants

What are foundations?

Foundations are a critical part of the structure that helps transfer load from the structure to the ground. The foundation is part of the structure on which the building stands. Hence, the consultants for structural design consider the foundation to be a critical member of the structure. The ground on which the foundation rests is the foundation bed.

Construction of the foundation needs excavation of the earth up to the required depth. The foundation depth is the distance from the natural ground level to the lowest point of the foundation construction.

Why is a foundation an essential element of the structure?

The foundation is an essential element due to the following: 

1. It distributes the weight of the structure over a large area of soil.
2. The foundation avoids unequal settlement.
3. The foundation helps prevent the lateral movement of the structure.
4. It increases structural stability.
5. It helps anchor the structure against natural forces. 
6. The foundation provides a level surface for construction.
7. The foundation anchors the structure into the ground, improving stability and avoiding overloading.

Characters of a good foundation

A well-performing foundation must have the following characteristics:

• The design and construction of the foundation must sustain and transmit the dead and the imposed loads to the soil. The transfer of loads should not result in any settlement that can cause stability issues.
• The foundation should avoid differential settlements by a rigid base, especially where the superimposed loads are not uniform.
• The consultants should also look into the temperature changes that may cause shrinkage and swelling while designing the foundation. 
• The location of the foundation chosen must be an area that is not affected or influenced by future works or factors.

Types of Footing

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

Shallow Foundations

In a shallow foundation, the depth is less and, hence, economical. It is typically for lightweight structures. Shallow foundations are of the following types:

1. Isolated Spread Footing: These footings are economical. These footings transfer the load of the columns to the soil. They could be rectangular, square, or round. The structural design consultant may or may not add reinforcement. The structural design consultants design such footings when no differing settlements are there under the structure. Such structures help when the structural load is low, and soil bearing capacity is high at a shallow depth. 
2. Wall Footing or Strip footing: Also known as continuous footing. These footings distribute the loads of the structure so as not to outperform the capacity of the soil. Structural consultants go for wall footing when loads are small, and the soil is dense. 
3. Combined Footing: These footings form a part of the structure with soil of low bearing capacity. The footings overlap each other. In this case, the foundations are often common to multiple columns. Such foundations help in a uniform distribution of load. These foundations are economical when placed too closely, or a footing on one side has restricted dimensions.  
4. Cantilever or Strap Footing: These are similar to combined footings. But the foundations under the columns are built individually and a strap connects them. Structural consultants use this type of footing when extending the footing’s edge beyond the property line is impossible. The exterior footing is connected with a strap beam.
5. Raft or Mat Foundation: is designed where the other foundations are unsuitable, or the bearing capacity of soil is inadequate. Structural consultants use these foundations when the structural load distribution is over a large area, or the structure has to bear continuous jerks and shocks. Additionally, it is the foundation of choice to prevent differential settlement. 

Deep Foundations

There are several types of deep foundations. Some of the common types of deep foundations that consultants foe structural design recommend are as follows: 

1. Pile Foundation: This is the most common type of deep foundation. Pile reduces the cost when shallow foundations cannot transmit the loads due to soil properties. In such cases, the pile transfers the loads to deeper soil or rocks. This foundation resists uplift by the structures and stabilises the building in lateral forces. Some of the conditions when a structural consultant recommends pile foundation are : 
   1. The soil has great bearing capacity at a depth.
   2. Irrigation canals are in the vicinity.
   3. Raft is expensive
   4. Also when there are concentrated heavy loads on the foundation. 
   5. Marshy areas
2. Pier Foundation: Piers are shallower than piles. The consultants design pier foundations in multi-storey structures. They go for pier foundations when: 
   1. There is a rock strata under a decomposed rock layer at the top.
   2. The topsoil is stiff clay and not suited for piling.
   3. A heavy load is to be transferred to the soil.
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 design foundations based on the geotechnical analysis of the soil. The key deciding factors are settlement and bearing capacity. Structural consultants design total settlement and differential settlement differently. As in differential settlement, a part of the foundation settles more than another part. 

Factors for deciding the foundation type

1. Ground type: The structural consultants and engineers determine whether the soil is clay, loamy, silt, hard rock, soft rock, etc. 
2. Load: It also depends on the actual load to be passed to the ground
3. Availability of equipment and materials: A major factor is the availability of equipment, materials and technology for the foundation at the site. 
4. The consultants also consider geographical conditions like proximity to water bodies, vegetation, and contours. 

To conclude, the foundation is a critical structural supporting member that passes the load from the beam, wall, or slab to the earth. It provides stability to the structure. The consultants for structural design ensure that the structure can withstand the loads throughout its lifespan.