Soil testing or study: what it is and why it should be done before building a house

Soil testing

Soil testing is a study that is practised on the ground before designing a construction, also called a geotechnical study, and with it the type of land where it is going to be built, characteristics and properties are defined.

What is soil testing done for?

This study is carried out to define the type of structure and foundation that is needed in a certain place.

What can the result of the soil study change in a design?

The ground is the base where the house will be built and it already exists, without the possibility of modification, so the design of the house must correspond to the ground where it will be built.

What information is very important to know in the soil study?

It is important to know if there are underground water bodies and at what depth they are since this situation can affect the behaviour of some types of soil.

When the soil study indicates it and depending on the load that the building will have, suitable solutions are sought for this situation, such as the deep foundation with the design of piles that will distribute the loads on the ground correctly.

In this article, we will briefly see what concerns soil studies for house construction.

Soil mechanic

What is soil mechanics?

It is the study of the application of the laws of physics and natural sciences on problems involving the loads imposed on the surface layer of the earth’s crust:

  • On the terrestrial surface, the constructions that are carried out are supported, in one way or another.

  • The earth is also used in different types of constructions such as embankments, dikes, fillings and other works in general.

For this reason, it is important to know the characteristics of the soils, in which these works are supported and in which the earth is used as a construction element.

In soil analyzes, the following must be defined in the first instance:

  • Its stability.

  • Functional behaviour.

Not taking the soil study into consideration, it can lead to certain negative situations in buildings, such as the following:

  • Deformations in the structure of the building.

  • Fissures

  • Cracks

  • Warping of the structure.

  • Construction collapse, in extreme situations.

The soil is the element where the construction is sustained and the foundations are those that are between the soil and the structure, for which the characteristics of the soils are studied and the appropriate foundations can be designed.

On what types of soils can a house be built?

In reality, there are different types of soils, some more suitable for building than others. In the most suitable soils, the design and cost of the foundations will be easier and less expensive to execute than in the less suitable soils.

Characteristics of the types of soils most suitable for building on them

  • Choosing a soil suitable for construction is more feasible, lower cost and lower maintenance, than land, which, however beautiful it may be, but which, due to its characteristics, requires complex designs in the foundation of the construction, more expensive and with a higher risk of short and long term maintenance.

  • Not all soil is suitable to build on, if cost, safety and maintenance are taken into account.

What are the most suitable soils to build on?

The most suitable soils to build on are soils composed of gravel and sand.

Characteristics of gravel and sand soils:

  • Composed of this type of soil: tiny stone particles that can be seen with the naked eye, larger stones.

  • Firmer ground.

  • Seismic waves are less amplified.

  • Resistant to loads.

What are the least suitable soils to build on them?

The least suitable soils for building houses are clay and silt soils.

soil characteristics

Characteristics of clay and silt soils:

  • It is made up of clays and silts that are tiny particles like dust.

  • Although they have good cohesion, they suffer great changes with water.

  • Resistance depends on the degree of humidity to which they are exposed.

  • Moisture from underground water bodies can directly affect this type of soil.

Variables that are analyzed in the soil study before building a house:

The variables that are analyzed in the soil study before construction are the following:

Characteristics of the soil suitable for building

  • Texture: Coarse

  • Colour: Gray

  • Particle shape: Angular

  • Unit weight: Heavy.

  • Granulometry: Various sizes.

  • Pre-consolidation: Compact and firm.

  • Water table: No water or deep.

  • Plasticity: Not plastic.

  • Expansion: Non-expansive.

  • Dispersion: Not dispersed.

  • Collapsible: Stable.

  • Organic material: No organic material.

When should the soil study be done?

  • In small constructions and with others built in their proximity with exposed, good quality soils suitable for construction, the average resistance of the soils is taken and a particular study of the land in question is not necessary.

  • In a land of doubtful aspect or in constructions of medium and large dimension, it is mandatory to take the precaution of doing the soil analysis.

How does the soil study influence the costs of building a house?

The testing soil study gives the physical, chemical and mechanical characteristics of the soil.

If this study is not done, its type is generally estimated depending on the constructions made in its environment for the design and calculation of the foundations.

When, due to not having the soil study, the foundations are oversized, this leads to a considerable increase in the cost of the construction of the house.

Recommendation: The soil study specifies exactly what type of foundation the house should have and thus adjusts to what is needed without unnecessary additional costs.

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