Guide to geotechnical site investigation

Why is my structural Engineer/Architect suggesting I may need a geotechnical site investigation?

Do I need a geotechnical site investigation?

All buildings need to be supported on the ground through their foundations. Whilst you cannot normally see a buildings foundations they are a vital part of the design of any building. Foundation failures such as subsidence result in damage to the buildings that the support ranging from unsightly cracking to sloping floors and even structural collapse in extreme cases.


Foundation Design

Foundations are designed based upon ground information. The geotechnical site investigation is completed in order to understand the nature of the ground, its strength, groundwater profile, soakaway potential, depth to bearing strata and the presence of any potentially harmful contaminants. Site investigations from a specialist geotechnical engineer will inform the design of foundations and sub-structure of any development and is an important part of the planning stage of a development project.



building regulation application

Site Investigation Process

The process is at least a two-phase approach which involves an initial desktop study followed by initial intrusive groundwork and geotechnical testing. The results of this will be reviewed and further investigation may be required if unusual conditions are encountered or additional data is needed for the proposed foundation design (such as piled solutions). The collection of samples and data points using various intrusive ground methods, can help assess the ground conditions on a site.



Minimises Damage

If you construct your building project without an understanding of the ground that is below, there is an increased chance that you will experience damage or issues with the building in the future. These may include settlement/subsidence caused by exceeding the strength of the ground, unknown voids (such as mines), soil changes in volume due to moisture changes or slope stability failure (landslip).

Construction quality inspection

This will provide valuable information for the structural engineer on the best solution for the design of the sub-structure.

Other issues will also not be adequately understood, the need for protection from ground borne gasses or contamination in the soil that may be hazardous to health or degrade the strength of the foundations themselves.

A suitable foundation designed with an understanding of the ground that supports it will work to protect your building or home.

On challenging sites or areas with known issues it can be essential to have a geotechnical investigation engineer check your site before the foundation is designed. They’ll help identify any risks of constructing at the site, which can help find the best solution. This may be using a specific design, materials, or treatments, or it may even mean finding a more suitable location.

How are geotechnical tests carried out?

The collection of samples and data points are aided using various intrusive ground methods, in both the near-surface and deep soil structure through techniques such as hand pitting, windowless sampling, cable percussive drilling and rotary coring. The samples are analysed in a specialist laboratory and the data passed to the geotechnical engineer for interpretation.

Geotechnical site investigations are tailored to the client specifications and architectural; concepts as well as contributing to the development of the structural design of future construction.


geotechnical site investigation

Can site investigation can increase the safety of the project?

On some projects and in certain areas it can be essential to carry out a site investigation to help determine how safe it is to move forward with your project. Constructing on or in certain soils or ground conditions may pose a threat to the workers and to existing buildings nearby. Conducting a site investigation with a qualified professional can minimise your risk and avoid any legal implications of failure. The importance of a site investigation cannot be stressed enough, it helps to determine several aspects of a project, which include lowering costs and improving safety. Every developer should consider undertaking a site investigation for their next project, if need to discuss this further please contact us.

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