Guide for conducting a geotechnical study: Key steps and recommendations

1. What is a geotechnical study and why is it important?

The geotechnical study is the process of analysing the physical and mechanical properties of the soil on a specific site. Its main objective is:

• To assess the strength and bearing capacity of the soil.

• To detect potential risks, such as the presence of groundwater or ground instability.

• To recommend the most suitable type of foundation for the project.

In addition to enabling safe and economical design for the construction, the study results prevent future problems such as cracks, excessive settlement or collapse, thereby avoiding costly over-runs or repairs later on.

2. Planning and collecting information beforehand

Before starting the fieldwork, it is essential to gather all the preliminary information available:

1. Existing documentation: Review topographical plans, previous studies or old reports that may provide data about the area.

2. Climatic and geological characteristics: Understand the climate, rainfall regime and geological formation of the region.

3. Local regulations: Ensure compliance with the specific legal requirements and obligations of the site where construction will take place.

This planning stage not only speeds up the process, but also optimises resources and ensures that geotechnical investigations are carried out in the most efficient way possible.

3. Fieldwork: Boreholes and sampling

Fieldwork is essential to obtain representative soil samples and to understand in detail their composition. The most common steps are as follows:

3.1 Geotechnical boreholes

Using specialised machinery, the ground is drilled to the required depth (usually down to the planned foundation level). During the process, soil cores or samples are extracted, enabling the geological strata and their strength characteristics to be identified.

3.2 Bores, pits and trial trenches

Depending on the ground type and the scope of the project, the geotechnical team may use trial trenches (shallower trenches) or pits at greater depth. These techniques facilitate direct observation of the soil stratigraphy and the taking of undisturbed samples for accurate testing.

3.3 Recording observations

It is crucial to keep a detailed photographic and written record of each stage: the depth of the boreholes, the colour and consistency of the soil, the presence of water or rocks, and any other feature relevant to the geotechnical assessment.

4. Laboratory tests to evaluate the soil properties

Once the samples have been obtained, various laboratory tests are carried out to determine characteristics such as:

• Particle size distribution: Size and distribution of particles (sand, silt, clay, etc.).

• Atterberg limits: Plasticity and consistency of the soil.

• Density and moisture content: How much water the ground can retain and the extent to which its mechanical behaviour changes.

• Shear strength: Determines the bearing capacity and stability under applied stresses.

These tests provide quantitative data that form the basis for any structural calculation and for the subsequent selection of the appropriate foundation type.

5. Interpretation of results and geotechnical report

Once the field and laboratory tests have been completed, the geotechnical team interprets and analyses the information obtained. From there, the geotechnical report is produced:

1. Site description: Includes stratigraphic composition and hydrogeological conditions.

2. Design parameters: Resistance values, cohesion and friction angle, among others, are specified.

3. Foundation recommendations: The type of foundation (shallow, deep or piled/combined) that ensures the safety and durability of the structure is suggested.

4. Risks and special considerations: Possible hazards are identified, such as the presence of groundwater, zones with expansive clays or areas of uncontrolled fill.

This report is extremely important for architects, engineers and contractors, as it defines the project’s feasibility and provides guidelines for designing stable structures.

6. Foundation selection and structural design

Based on the data from the geotechnical study, the foundation solution that best suits the project is selected:

• Shallow foundations: Ideal for soils with good bearing capacity and smaller-scale constructions.

• Deep foundations: Used in ground with weak near-surface strata or when the building is large and requires greater stability.

• Combined or special systems: Used in cases where there are significant variations in the soil or very particular geological conditions.

In this way, the structural design starts from a solid and reliable base, minimising the possibility of differential settlement or structural failures.

7. Conclusions and final recommendations

A properly executed geotechnical study is the key to ensuring that any construction is carried out on safe and durable foundations. Although it may involve an initial cost, in the long term it is an investment that avoids costly damage and provides the peace of mind that the ground has been assessed by specialised professionals.

If you are considering starting a construction project, remember:

• Hire a team of geotechnical professionals with experience and appropriate equipment.

• Don’t skimp at this stage: a good geotechnical study can make the difference between a successful project and one with future problems.

• Make sure you review the geotechnical report in detail and follow the recommendations for the foundation and structural design.

Having a geotechnical study is, in short, an essential step for any safe and durable work. Don’t hesitate to contact us if you need more information on how to carry out or interpret a soil study before embarking on your next project!