What happens if a foundation is designed without knowing the mechanical properties of the soil in detail?
The risk of differential settlement, overall instability, or even structural failure can increase exponentially. This is why it is so important to first conduct a geotechnical study, an essential tool in the design and planning phase of any infrastructure project.
A geotechnical study not only determines the soil's bearing capacity but also makes it possible to anticipate risks associated with soil-structure interaction, optimize foundation costs, and ensure long-term safety. These same subsoil investigations are equally critical in the energy sector, such as in the use of Geothermal Energy and the Design of Geothermal Power Plants, where knowledge of the site's thermal and geological properties determines the project's feasibility.
In this article, we will discuss what a geotechnical study is, its main phases, the most commonly used techniques, and its role in modern engineering.
What is a geotechnical study?
A geotechnical study It is the systematic investigation of the subsurface intended to characterize its geomechanical, hydrogeological, and chemical properties, in order to evaluate its interaction with the loads and service conditions of a structure.
Its scope includes:
- Stratigraphic characterization using boreholes, test pits, and in-situ tests (SPT, CPTu, pressuremeter, dilatometer, geophysical methods).
- Determination of mechanical parameters: cohesion (c), angle of friction (φ), modulus of deformation (E, M), undrained strength (su).
- Hydrogeological conditions: water table level, permeability, and seasonal variations.
- Soil behavior: thrusts, underpressure, liquefaction potential, expansive behavior, or collapse.
- Chemical aggressiveness of soil and groundwater toward concrete and steel.
What does a geotechnical study include?
The process generally consists of three stages:
- Fieldwork:Drilling, test pits (trial excavations), and testing are carried out on site to collect subsurface samples and record the characteristics of the soil at different depths.
- Laboratory Analysis: The collected samples are analyzed in a laboratory to determine their properties (strength, particle size distribution, plasticity, etc.)
- Preparation of the geotechnical report: A detailed report is created that summarizes the findings, presents the conclusions, and offers specific recommendations for the design and execution of construction projects.
Structures that do not require a geotechnical study
If the building meets the following conditions (all 5 must be met), it will not be subject to the LOE and the CTE, and therefore this study is not required:
- If the building is technically simple.
- It has little structural significance.
- It has only one floor.
- It is neither residential nor public in nature.
- It must not compromise people's safety.
It is very difficult for a building to meet these five conditions; that is why It is practically mandatory to have a geotechnical study.
Buildings to Which the CTE Applies
The CTE specifies the buildings regulated by this law, which, therefore, require a geotechnical study:
- The homes in residential use, including self-built single-family homes.
- All the public buildings, such as a sports arena, a library, a municipal warehouse, prefabricated modules used in schools, etc.
- All the industrial buildings that may affect public safety, such as an industrial warehouse, auxiliary buildings for staff, offices, agricultural sheds, etc.
Facilities that partially comply with the CTE
These are the ones that only require a geotechnical study to one of its parts. For example, wastewater treatment plants or swimming pools, since only their annex requires a geotechnical study.
The following are not included in the CTE
These include ports, viaducts, bridges, power transmission towers, etc. Most of these structures have internal regulations which specify whether or not a geotechnical study is required.
Who is responsible for conducting the required geotechnical study?
To be on the safe side, it’s best to consult the relevant legislation. Whenever the LOE—and, therefore, the CTE—applies, a geotechnical study must be conducted. These are the regulations governing technical studies and their mandatory nature:
- The Building Regulations Act (LOE). Also known as Law 38/1999, it has been in effect since 2000. It establishes the essential obligations that must be met by those involved in the construction process to ensure the quality of the site where construction will take place and to protect the interests of individuals.
- The Technical Building Code (CTE) Royal Decree 314/2006 expands upon the Building Regulations Act, establishing the requirements that buildings must meet with regard to the basic safety and habitability standards set forth in the LOE. Section 3.1.6 of the CTE specifies that «responsibility for the geotechnical study shall lie with the designer, another qualified technician, or, where applicable, the construction manager.».
- In addition, if we are going to build a concrete structure, we must also take the following into account:
- The Structural Concrete Code (EHE), that Royal Decree 470/2021, dated June 29, approving the Structural Code. It governs the design, construction, and inspection of concrete structures in both building and civil engineering projects. In this way, it ensures that these structures meet the necessary safety standards.
Each professional association determines the qualifications required to conduct a geotechnical study. Traditionally, these include geologists, civil engineers, and architects. In this context, it is worth noting that some of the The Most In-Demand Engineering Roles Today These positions are specifically for professionals with advanced training in geotechnical engineering, foundations, and soil engineering, which underscores the strategic importance of this specialty.
Recommended education for conducting geotechnical studies
A geotechnical study requires very specific knowledge that not every ICCP, architect, or geologist possesses. It is best to have a master’s degree, such as the International Master’s in Geotechnics and Foundations. The program emphasizes numerical modeling in geotechnics, and its case studies and practical exercises provide the experience necessary to perform a Mandatory geotechnical study.
