What is geotechnics? The invisible foundation of every construction

Essential to carry out a geotechnical study before building

Geotechnics is a fundamental discipline that is often overlooked by the general public, but which is essential in any construction project. When we look at a building, a bridge or a road, we rarely think about what lies beneath it: the ground that supports it. However, it is precisely that interaction between soil and structure that determines the safety, durability and feasibility of any construction.

In this article, we will explore what geotechnics is exactly, why it is essential to carry out a good geotechnical study before building, and how this field of civil engineering protects us all in our day-to-day lives.

What is Geotechnics? Definition and scope

Geotechnics is the branch of civil engineering that studies the mechanical, hydraulic and physical properties of terrestrial materials—especially soils and rocks—and their application to engineering problems. This field combines principles of soil mechanics, rock mechanics, geology and hydrology to analyse the interaction between structures built by human beings and the ground on which they sit.

Unlike other engineering disciplines that work with manufactured materials under controlled standards, geotechnics deals with natural materials that have heterogeneous and variable properties. A geotechnical engineer must:

• Determine the physical characteristics and behaviour of the ground
• Assess the bearing capacity of the soil
• Predict possible settlements and deformations
• Estimate the stability of slopes and excavations
• Recommend the most suitable foundation systems
• Identify and mitigate geological risks

History and evolution of Geotechnics

Geotechnics as a scientific discipline is relatively recent, although mankind has faced challenges related to the ground since the first constructions.

From empirical experience to modern science

For centuries, builders relied mainly on observation and accumulated experience to determine whether a ground was suitable for construction. The Romans, for example, developed advanced foundation techniques based on practical knowledge. However, it was not until the 20th century that geotechnics was established as a formal scientific discipline.

Karl Terzaghi, considered the “father of modern soil mechanics”, published in 1925 his work “Erdbaumechanik” (Soil Mechanics), establishing the theoretical foundations of the discipline. From then on, driven by the development of major engineering works and some notable structural failures, geotechnics experienced rapid development both in its theoretical framework and in investigation techniques.

The Geotechnical study: the cornerstone of safe construction

What is a geotechnical study?

A geotechnical study is an investigation of the subsoil that analyses and characterises the materials on which a construction will be founded. This study provides crucial information to properly design foundations and other structures that interact with the ground.

Phases of a good complete geotechnical study

1. Preliminary investigation: Collection of existing information about the area (geological maps, history of nearby constructions, etc.)
2. Fieldwork: Carrying out boreholes, trial pits, penetration tests and other techniques to obtain samples and ground data.
3. Laboratory tests: Analysing the samples to determine properties such as particle size distribution, plasticity, strength, compressibility, etc.
4. Analysis and interpretation: Processing all obtained data to characterise the ground and its behaviour.
5. Technical recommendations: Proposal of construction solutions tailored to the specific conditions of the ground.

When is a geotechnical study mandatory?

In Spain, current regulations (Código Técnico de la Edificación, CTE) establish the requirement to carry out geotechnical studies for practically any type of building. The extent and depth of the study vary depending on the complexity of the structure and the geological characteristics of the area.

Techniques and tests in geotechnical investigation

Field techniques

Geotechnical professionals have a wide range of techniques to investigate the ground:

Mechanical boreholes

These make it possible to obtain continuous ground samples at different depths. There are various types:

• Rotary boreholes with core recovery
• Percussion boreholes
• Helical boreholes

Penetration tests

They measure the resistance of the ground to penetration of a standardised device:

• Standard penetration test (SPT)
• Dynamic penetration test (DPSH, DPH, DPM, DPL)
• Static penetration test or Dutch cone (CPT, CPTU)

Trial pits

Shallow excavations that allow direct observation of the ground and sampling.

Geophysical tests

Non-destructive methods that use physical principles to investigate the subsoil:

• Seismic refraction
• Electrical tomography
• Ground-penetrating radar

Laboratory tests

The samples obtained in the field are subjected to various analyses:

• Identification tests: particle size distribution, Atterberg limits
• State tests: density, moisture content
• Strength tests: unconfined compression, direct shear, triaxial
• Deformability tests: oedometer test, consolidation
• Chemical tests: sulphate content, organic matter, pH

Applications of geotechnics in different sectors

Residential and commercial buildings

In the building sector, geotechnics is fundamental for:

• Designing safe and economical foundations
• Preventing structural damage due to differential settlements
• Minimising the impact on neighbouring buildings
• Planning excavations and earth retention

Civil engineering works

Large-scale infrastructures pose particular geotechnical challenges:

• Dams: stability, seepage, internal erosion
• Tunnels: behaviour of the rock mass, support
• Bridges: bearing capacity at abutments and piers
• Roads: slope stability, pavement behaviour

Special projects

Some projects require especially detailed geotechnical studies:

• High-rise buildings or structures with exceptional loads
• Construction in seismic zones
• Infrastructure on problematic ground (expansive, collapsible, karstic)
• Rehabilitation of historic buildings

Common geotechnical problems

Expansive soils

These soils undergo significant volume changes with variations in moisture. In Spain, they are particularly frequent on the central plateau and in the Guadalquivir valley. An appropriate geotechnical study makes it possible to identify them and design specific solutions such as:

• Reinforced and deep foundations
• Barriers against moisture changes
• Ground improvement treatments

Karstic ground

Karst formations, characterised by the dissolution of limestone rocks and the formation of cavities, present risks of sudden sinkholes. Detection requires:

• Advanced geophysical methods
• A higher density of reconnaissance points
• Complementary hydrogeological studies

Slope instability

Ground landslides can severely affect structures. Geotechnics enables:

• Assessing the natural stability of the slope
• Designing retaining and drainage systems
• Monitoring movements to detect early-warning signals

Benefits of a good geotechnical study

Guaranteed safety

Without doubt, the main benefit is safety. A complete geotechnical study identifies potential risks and allows solutions to be designed that ensure the stability of the construction throughout its service life.

Economic optimisation

Although it involves an initial investment, a good geotechnical study allows construction solutions to be optimised, avoiding:

• Unnecessary over-sizing
• Modifications during execution
• Costly repairs due to problems not detected
• Litigation arising from damage to third parties

A study costing between 0.1% and 0.5% of the total budget can save up to 20% in foundation costs and prevent problems that could multiply the final cost.

Sustainability and respect for the environment

Modern geotechnics incorporates sustainability criteria:

• Minimising earthworks movement
• Reusing excavated materials
• Low environmental-impact ground improvement techniques
• Solutions adapted to the natural environment

How to choose a good geotechnical study service

Selection criteria

When commissioning a geotechnical study, it is worth assessing:

• Experience and specialisation in similar projects
• Technical equipment available
• In-house laboratory or accredited collaborators
• Ability to interpret data and provide advice
• References from previous clients

Documentation and deliverables

A professional geotechnical study should provide:

• Complete descriptive report
• Annexes with field and laboratory test data
• Clear stratigraphic profiles
• Specific recommendations for the project
• Advice during the design and execution phases

Geotechnics as an investment in safety and quality

Geotechnics, far from being a mere administrative formality or an additional expense, is a fundamental investment in the safety, durability and economy of any construction project. A rigorous geotechnical study provides the knowledge needed to make the right decisions from the earliest stages of the project.

In a context where the most favourable ground has already been taken up and technical requirements are increasingly demanding, geotechnics becomes an indispensable tool for meeting the construction challenges of the 21st century. Relying on experienced professionals not only complies with current regulations, but also guarantees peace of mind that we are building on solid foundations, both literally and figuratively.

Remember: no construction is better than its foundations, and no foundation is better than knowledge of the ground on which it rests.