Guide to Shallow Foundations: Types, Calculations, and Differences from Deep Foundations

Shallow foundations are one of the most important elements in any building project, since they constitute the system that transfers the structure's loads to the ground. Their proper selection and design directly affect the stability, safety, and durability of a building.
In the the field of foundations in architecture, These types of solutions are used when the soil provides adequate bearing capacity at shallow depths, thereby avoiding the need for more complex solutions such as deep foundations.

When is a foundation considered shallow, and in what situations is it used?

Foundations are considered shallow foundations when the The transfer of loads to the ground occurs at a shallow depth, generally less than the width of the foundation itself.
They are mainly used when:

• The surface soil has good bearing capacity
• The building's loads are not excessively high
• There are no resistant strata at great depths
• These are low- or mid-rise buildings

They are common in single-family homes, small residential buildings, and light-frame structures.

How to Calculate and Design a Shallow Foundation

The design of shallow foundations is based on ensure that the ground can support the loads without suffering excessive deformation or failure due to subsidence.
The general calculation process includes:

• Geotechnical Study of the Site
• Determination of the Building's Structural Load
• Calculation of the Allowable Soil Stress
• Sizing the Support Surface
• Verification of Seats and Stability

The goal is for the pressure transmitted to the ground is always less than its bearing capacity.

Practical Example

Let's imagine a single-family home with a total load of 300 kN and a site with an allowable stress of 150 kN/m².
The minimum required foundation area would be:
300 kN ÷ 150 kN/m² = 2 m²
This means that The foundation must cover an area of at least 2 square meters. to ensure structural safety.

Differences Between Shallow and Deep Foundations

The differences between the two systems They are essential among the types of foundations used in engineering and architecture.

The Shallow and deep foundations do not compete with each other, rather, they are chosen based on the characteristics of the site and the project.

Types of Shallow Foundations

There are several types shallow foundation systems, each tailored to different structural needs.

Soles

A strip foundation is the the most common solution for shallow foundations. It consists of a widened concrete foundation that distributes the load from a column or wall to the ground.
They are cost-effective, easy to implement, and widely used in residential construction.

Types of shoes

• Isolated sole. It is used to support a single column. It is the most common type in homes and small buildings, since it distributes the load at specific points on the ground.
• Running shoes. It is placed under walls or rows of nearby columns. It distributes the load evenly across the ground.
• Combination shoe. Designed for two or more adjacent columns when it is not possible to use separate footings. It allows for better load balancing.
• Eccentric or party wall footing. It is used when the column is close to a boundary or a dividing wall. It usually requires additional components to compensate for the load.

Foundation slabs or plates

Foundation slabs are a continuous solution which distributes the loads of the entire structure over a large area.
They are used when:

• The soil has low bearing capacity
• There are heavy or irregular loads
• The goal is to reduce differential seats

This type of foundation is very common in basements or multi-story buildings on difficult terrain.

Requirements for Shallow Foundations

To ensure they function properly, shallow foundations must meet a series of Technical requirements:

• Stability vs. Sinking
• Differential Seat Control
• Adequate structural strength
• Terrain Compatibility
• Resistance to Moisture and External Factors

Compliance with these conditions is essential for the building's long-term safety.

Other Frequently Asked Questions About Shallow Foundations